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  • Aircraft Propulsion and Power
  • Ecology
  • 2010-2014  (336)
  • 1950-1954  (38)
  • 1935-1939  (5)
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  • 1
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    Nature Publishing Group (NPG)
    Publication Date: 2010-11-05
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lunt, Dan -- England -- Nature. 2010 Nov 4;468(7320):37. doi: 10.1038/468037c.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21048749" target="_blank"〉PubMed〈/a〉
    Keywords: Computer Simulation ; Ecology ; *Periodicals as Topic/trends ; *Publishing/trends ; *Software/standards
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
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    Nature Publishing Group (NPG)
    Publication Date: 2010-06-04
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schrope, Mark -- England -- Nature. 2010 Jun 3;465(7298):540-2. doi: 10.1038/465540a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20520684" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Conservation of Natural Resources/economics/legislation & jurisprudence/*methods ; Ecology ; Fisheries/economics/legislation & jurisprudence/*methods/statistics & numerical ; data ; Fishes/physiology ; Marine Biology ; New England
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
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    Nature Publishing Group (NPG)
    Publication Date: 2010-05-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉England -- Nature. 2010 May 13;465(7295):135-6. doi: 10.1038/465135b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20463694" target="_blank"〉PubMed〈/a〉
    Keywords: Ecology ; *Global Warming ; Humans ; Research Personnel/*legislation & jurisprudence ; *State Government ; Universities/*legislation & jurisprudence ; Virginia
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 4
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    Nature Publishing Group (NPG)
    Publication Date: 2010-08-13
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schrope, Mark -- England -- Nature. 2010 Aug 12;466(7308):802. doi: 10.1038/466802a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20703275" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Disasters/*statistics & numerical data ; Ecology ; *Ecosystem ; Marine Biology ; Oceanography ; Oceans and Seas ; Petroleum/adverse effects/*analysis ; Reproducibility of Results ; Seawater/*chemistry ; *Uncertainty ; Volatilization
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
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    Nature Publishing Group (NPG)
    Publication Date: 2010-05-21
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schrope, Mark -- England -- Nature. 2010 May 20;465(7296):274-5. doi: 10.1038/465274a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20485402" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Disasters ; Ecology ; Ecosystem ; Geologic Sediments/chemistry ; Marine Biology ; Oceans and Seas ; Petroleum/adverse effects/*analysis/supply & distribution/toxicity ; Seawater/*chemistry ; *Ships ; Water Movements
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2010-09-11
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mayer, Paul -- England -- Nature. 2010 Sep 9;467(7312):153. doi: 10.1038/467153b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20829773" target="_blank"〉PubMed〈/a〉
    Keywords: *Cities ; Conservation of Natural Resources ; Ecology ; *Ecosystem ; Human Activities ; Humans ; Urban Population
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 7
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    Nature Publishing Group (NPG)
    Publication Date: 2010-10-29
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gilbert, Natasha -- England -- Nature. 2010 Oct 28;467(7319):1021. doi: 10.1038/4671021a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20981066" target="_blank"〉PubMed〈/a〉
    Keywords: *Altitude ; Aquatic Organisms/physiology ; *Coal ; Ecology ; *Ecosystem ; Electric Conductivity ; Mining/*legislation & jurisprudence ; Trees/physiology ; United States ; United States Environmental Protection Agency/*legislation & jurisprudence ; Water Pollution/*prevention & control ; West Virginia
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 8
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    Nature Publishing Group (NPG)
    Publication Date: 2011-11-19
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cressey, Daniel -- England -- Nature. 2011 Nov 16;479(7373):277. doi: 10.1038/479277a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22094665" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Coral Reefs ; Ecology ; *Ecosystem ; Environmental Monitoring ; Eutrophication ; Geography ; Iran ; Oceans and Seas ; United Arab Emirates
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 9
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    Nature Publishing Group (NPG)
    Publication Date: 2012-11-29
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉England -- Nature. 2012 Nov 22;491(7425):496.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23189323" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquatic Organisms/drug effects ; Ecology ; *Environmental Restoration and Remediation/economics/legislation & ; jurisprudence/trends ; Ethinyl Estradiol/adverse effects/analysis ; Fishes/abnormalities ; Great Britain ; International Cooperation ; *Water Purification/economics/legislation & jurisprudence ; *Water Supply/economics/legislation & jurisprudence
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 2012-01-10
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Florens, F B Vincent -- England -- Nature. 2012 Jan 4;481(7379):29. doi: 10.1038/481029b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22222742" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biodiversity ; Conservation of Natural Resources/*legislation & jurisprudence ; Ecology ; Environmental Policy/*legislation & jurisprudence ; Mauritius
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    Electronic ISSN: 1476-4687
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  • 11
    Publication Date: 2012-06-09
    Description: Evidence is mounting that extinctions are altering key processes important to the productivity and sustainability of Earth's ecosystems. Further species loss will accelerate change in ecosystem processes, but it is unclear how these effects compare to the direct effects of other forms of environmental change that are both driving diversity loss and altering ecosystem function. Here we use a suite of meta-analyses of published data to show that the effects of species loss on productivity and decomposition--two processes important in all ecosystems--are of comparable magnitude to the effects of many other global environmental changes. In experiments, intermediate levels of species loss (21-40%) reduced plant production by 5-10%, comparable to previously documented effects of ultraviolet radiation and climate warming. Higher levels of extinction (41-60%) had effects rivalling those of ozone, acidification, elevated CO(2) and nutrient pollution. At intermediate levels, species loss generally had equal or greater effects on decomposition than did elevated CO(2) and nitrogen addition. The identity of species lost also had a large effect on changes in productivity and decomposition, generating a wide range of plausible outcomes for extinction. Despite the need for more studies on interactive effects of diversity loss and environmental changes, our analyses clearly show that the ecosystem consequences of local species loss are as quantitatively significant as the direct effects of several global change stressors that have mobilized major international concern and remediation efforts.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hooper, David U -- Adair, E Carol -- Cardinale, Bradley J -- Byrnes, Jarrett E K -- Hungate, Bruce A -- Matulich, Kristin L -- Gonzalez, Andrew -- Duffy, J Emmett -- Gamfeldt, Lars -- O'Connor, Mary I -- England -- Nature. 2012 May 2;486(7401):105-8. doi: 10.1038/nature11118.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biology, Western Washington University, Bellingham, Washington 98225-9160, USA. hooper@biol.wwu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22678289" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biodiversity ; Ecology ; *Ecosystem ; *Extinction, Biological ; Models, Biological
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 12
    Publication Date: 2012-10-27
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tollefson, Jeff -- England -- Nature. 2012 Oct 25;490(7421):458-9. doi: 10.1038/490458a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23099379" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquatic Organisms/metabolism ; Canada ; Carbon Dioxide/metabolism ; *Carbon Sequestration ; Ecology ; Environmental Policy/*legislation & jurisprudence ; Oceans and Seas ; Phytoplankton/growth & development/metabolism ; Politics ; Salmon/*growth & development ; Seawater/*chemistry ; Uncertainty
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 13
    Publication Date: 2014-08-08
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kennicutt, Mahlon C 2nd -- Chown, Steven L -- Cassano, John J -- Liggett, Daniela -- Massom, Rob -- Peck, Lloyd S -- Rintoul, Steve R -- Storey, John W V -- Vaughan, David G -- Wilson, Terry J -- Sutherland, William J -- England -- Nature. 2014 Aug 7;512(7512):23-5. doi: 10.1038/512023a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Texas A&M University, College Station, Texas, USA, and past-president of the Scientific Committee on Antarctic Research. ; Monash University, Victoria, Australia. ; Cooperative Institute for Research in Environmental Sciences, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA. ; Gateway Antarctica, University of Canterbury, Christchurch, New Zealand. ; Australian Antarctic Division, and Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Australia. ; British Antarctic Survey, Cambridge, UK. ; Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania, Australia. ; School of Physics, University of New South Wales, Sydney, Australia. ; School of Earth Sciences, Ohio State University, Columbus, Ohio, USA. ; Conservation Science Group, Department of Zoology, University of Cambridge, Cambridge, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25100467" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Astronomy ; Atmosphere/chemistry ; Biological Evolution ; Budgets ; *Climate Change ; Conservation of Natural Resources/methods ; Ecology ; Exobiology ; Ice Cover ; International Cooperation ; Oceans and Seas ; *Policy Making ; Research/economics/*trends
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 14
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    Nature Publishing Group (NPG)
    Publication Date: 2014-06-27
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, Kerri -- England -- Nature. 2014 Jun 26;510(7506):458-60. doi: 10.1038/510458a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24965634" target="_blank"〉PubMed〈/a〉
    Keywords: Anthropology ; Cell Division ; *Cooperative Behavior ; Cultural Evolution ; Ecology ; Germany ; Humans ; *Laboratories ; *Love ; Phylogeny ; Research Personnel/*psychology ; Taiwan ; Travel ; Workplace
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 15
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    Nature Publishing Group (NPG)
    Publication Date: 2014-04-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tollefson, Jeff -- England -- Nature. 2014 Apr 17;508(7496):302-4. doi: 10.1038/508302a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24740049" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Birds ; Ecology ; *Electric Power Supplies/adverse effects/economics ; Electricity ; Internationality ; *Oceans and Seas ; *Water Movements ; Whale, Killer
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 16
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    Nature Publishing Group (NPG)
    Publication Date: 2012-04-07
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Qiu, Jane -- England -- Nature. 2012 Apr 2;484(7392):19. doi: 10.1038/484019a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22481333" target="_blank"〉PubMed〈/a〉
    Keywords: *Altitude ; Ecology ; Global Warming/*statistics & numerical data ; *Ice Cover ; *Research/trends ; Tibet ; Water Supply/*analysis
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 17
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    Nature Publishing Group (NPG)
    Publication Date: 2012-02-03
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schrope, Mark -- England -- Nature. 2012 Feb 1;482(7383):20-1. doi: 10.1038/482020a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22297950" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquatic Organisms/*growth & development/isolation & purification ; Cnidaria/*growth & development ; Ecology ; Internationality ; Marine Biology ; Population Growth
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 18
    Publication Date: 2012-06-23
    Description: Complex networks of interactions are ubiquitous and are particularly important in ecological communities, in which large numbers of species exhibit negative (for example, competition or predation) and positive (for example, mutualism) interactions with one another. Nestedness in mutualistic ecological networks is the tendency for ecological specialists to interact with a subset of species that also interact with more generalist species. Recent mathematical and computational analysis has suggested that such nestedness increases species richness. By examining previous results and applying computational approaches to 59 empirical data sets representing mutualistic plant-pollinator networks, we show that this statement is incorrect. A simpler metric-the number of mutualistic partners a species has-is a much better predictor of individual species survival and hence, community persistence. Nestedness is, at best, a secondary covariate rather than a causative factor for biodiversity in mutualistic communities. Analysis of complex networks should be accompanied by analysis of simpler, underpinning mechanisms that drive multiple higher-order network properties.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉James, Alex -- Pitchford, Jonathan W -- Plank, Michael J -- England -- Nature. 2012 Jul 12;487(7406):227-30. doi: 10.1038/nature11214.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Biomathematics Research Centre, University of Canterbury, Private Bag 4800, Christchurch 8040, New Zealand. alex.james@canterbury.ac.nz〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22722863" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biodiversity ; Ecology ; *Ecosystem ; *Models, Theoretical
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 19
    Publication Date: 2012-04-27
    Description: Numerous reports have emphasized the need for major changes in the global food system: agriculture must meet the twin challenge of feeding a growing population, with rising demand for meat and high-calorie diets, while simultaneously minimizing its global environmental impacts. Organic farming-a system aimed at producing food with minimal harm to ecosystems, animals or humans-is often proposed as a solution. However, critics argue that organic agriculture may have lower yields and would therefore need more land to produce the same amount of food as conventional farms, resulting in more widespread deforestation and biodiversity loss, and thus undermining the environmental benefits of organic practices. Here we use a comprehensive meta-analysis to examine the relative yield performance of organic and conventional farming systems globally. Our analysis of available data shows that, overall, organic yields are typically lower than conventional yields. But these yield differences are highly contextual, depending on system and site characteristics, and range from 5% lower organic yields (rain-fed legumes and perennials on weak-acidic to weak-alkaline soils), 13% lower yields (when best organic practices are used), to 34% lower yields (when the conventional and organic systems are most comparable). Under certain conditions-that is, with good management practices, particular crop types and growing conditions-organic systems can thus nearly match conventional yields, whereas under others it at present cannot. To establish organic agriculture as an important tool in sustainable food production, the factors limiting organic yields need to be more fully understood, alongside assessments of the many social, environmental and economic benefits of organic farming systems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Seufert, Verena -- Ramankutty, Navin -- Foley, Jonathan A -- England -- Nature. 2012 May 10;485(7397):229-32. doi: 10.1038/nature11069.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geography and Global Environmental and Climate Change Center, McGill University, Montreal, Quebec H2T 3A3, Canada. verena.seufert@mail.mcgill.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22535250" target="_blank"〉PubMed〈/a〉
    Keywords: Agricultural Irrigation ; Agriculture/*methods ; Animals ; *Biomass ; Conservation of Natural Resources/*methods ; Crops, Agricultural/classification/growth & development ; Developed Countries ; Developing Countries ; Ecology ; Ecosystem ; Food Supply/*statistics & numerical data ; Food, Organic/supply & distribution ; Forestry ; Humans ; Hydrogen-Ion Concentration ; Organic Agriculture/*methods ; Population Growth ; Soil/analysis/chemistry ; Time Factors
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    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 20
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    Nature Publishing Group (NPG)
    Publication Date: 2014-12-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Woolston, Chris -- England -- Nature. 2014 Dec 11;516(7530):277-9.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25517006" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquatic Organisms ; Career Choice ; Ecology ; Employment ; Internship and Residency ; Marine Biology/*education/*manpower ; Students ; *Vocational Guidance
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    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 21
    Publication Date: 2014-06-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Arzt, Eduardo -- Orjeda, Gisella -- Nobre, Carlos -- Castilla, Juan Carlos -- Baranao, Lino -- Ribeiro, Sidarta -- Bifano, Claudio -- Krieger, Jose Eduardo -- Guerrero, Pablo C -- England -- Nature. 2014 Jun 12;510(7504):209-12.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24926500" target="_blank"〉PubMed〈/a〉
    Keywords: Agriculture ; Animals ; Argentina ; Biodiversity ; Brazil ; *Capacity Building ; Chile ; Ecology ; Forestry ; Peru ; Public Policy ; Public-Private Sector Partnerships/economics ; Research Personnel/standards ; Reward ; Science/manpower/*organization & administration/standards ; Venezuela
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    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 22
    Publication Date: 2014-08-21
    Description: Genetic diversity is the amount of variation observed between DNA sequences from distinct individuals of a given species. This pivotal concept of population genetics has implications for species health, domestication, management and conservation. Levels of genetic diversity seem to vary greatly in natural populations and species, but the determinants of this variation, and particularly the relative influences of species biology and ecology versus population history, are still largely mysterious. Here we show that the diversity of a species is predictable, and is determined in the first place by its ecological strategy. We investigated the genome-wide diversity of 76 non-model animal species by sequencing the transcriptome of two to ten individuals in each species. The distribution of genetic diversity between species revealed no detectable influence of geographic range or invasive status but was accurately predicted by key species traits related to parental investment: long-lived or low-fecundity species with brooding ability were genetically less diverse than short-lived or highly fecund ones. Our analysis demonstrates the influence of long-term life-history strategies on species response to short-term environmental perturbations, a result with immediate implications for conservation policies.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Romiguier, J -- Gayral, P -- Ballenghien, M -- Bernard, A -- Cahais, V -- Chenuil, A -- Chiari, Y -- Dernat, R -- Duret, L -- Faivre, N -- Loire, E -- Lourenco, J M -- Nabholz, B -- Roux, C -- Tsagkogeorga, G -- Weber, A A-T -- Weinert, L A -- Belkhir, K -- Bierne, N -- Glemin, S -- Galtier, N -- England -- Nature. 2014 Nov 13;515(7526):261-3. doi: 10.1038/nature13685. Epub 2014 Aug 20.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] UMR 5554, Institute of Evolutionary Sciences, University Montpellier 2, Centre national de la recherche scientifique, Place E. Bataillon, 34095 Montpellier, France [2] Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland. ; 1] UMR 5554, Institute of Evolutionary Sciences, University Montpellier 2, Centre national de la recherche scientifique, Place E. Bataillon, 34095 Montpellier, France [2] UMR 7261, Institut de Recherches sur la Biologie de l'Insecte, Centre national de la recherche scientifique, Universite Francois-Rabelais, 37200 Tours, France. ; UMR 5554, Institute of Evolutionary Sciences, University Montpellier 2, Centre national de la recherche scientifique, Place E. Bataillon, 34095 Montpellier, France. ; Aix-Marseille Universite, Institut Mediterraneen de Biodiversite et d'Ecologie marine et continentale (IMBE) - CNRS - IRD - UAPV, 13007 Marseille, France. ; Department of Biology, University of South Alabama, Mobile, Alabama 36688-0002, USA. ; UMR 5558, Laboratoire de Biometrie et Biologie Evolutive, Universite Lyon 1, CNRS, 69622 Lyon, France. ; 1] UMR 5554, Institute of Evolutionary Sciences, University Montpellier 2, Centre national de la recherche scientifique, Place E. Bataillon, 34095 Montpellier, France [2] The School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK. ; 1] UMR 5554, Institute of Evolutionary Sciences, University Montpellier 2, Centre national de la recherche scientifique, Place E. Bataillon, 34095 Montpellier, France [2] Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25141177" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Ecology ; *Evolution, Molecular ; Genetic Variation/*genetics ; *Genetics, Population ; Genome/*genetics ; *Genomics ; *Phylogeny
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 23
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    Unknown
    Nature Publishing Group (NPG)
    Publication Date: 2011-07-08
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Alyokhin, Andrei -- England -- Nature. 2011 Jul 6;475(7354):36. doi: 10.1038/475036b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21734688" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Australia ; Conservation of Natural Resources ; Ecology ; Introduced Species/*statistics & numerical data
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 24
    facet.materialart.
    Unknown
    Nature Publishing Group (NPG)
    Publication Date: 2012-03-09
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉England -- Nature. 2012 Mar 7;483(7388):123-4. doi: 10.1038/483123b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22398516" target="_blank"〉PubMed〈/a〉
    Keywords: Ecology ; Great Britain ; History, 20th Century ; Internationality ; National Socialism/history ; Physics/history ; *Politics ; Religion and Science ; *Science
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 25
    Publication Date: 2014-01-10
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Harfoot, Mike -- Roberts, Dave -- England -- Nature. 2014 Jan 9;505(7482):160. doi: 10.1038/505160a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉United Nations Environment Programme World Conservation Monitoring Centre, and Microsoft Research, Cambridge, UK. ; Natural History Museum, London, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24402271" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Classification ; Computational Biology ; Databases, Factual ; Ecology ; *Ecosystem ; *Models, Biological
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 26
    Publication Date: 2011-01-29
    Description: The effect of ecological change on evolution has long been a focus of scientific research. The reverse--how evolutionary dynamics affect ecological traits--has only recently captured our attention, however, with the realization that evolution can occur over ecological time scales. This newly highlighted causal direction and the implied feedback loop--eco-evolutionary dynamics--is invigorating both ecologists and evolutionists and blurring the distinction between them. Despite some recent relevant studies, the importance of the evolution-to-ecology pathway across systems is still unknown. Only an extensive research effort involving multiple experimental approaches-particularly long-term field experiments--over a variety of ecological communities will provide the answer.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schoener, Thomas W -- New York, N.Y. -- Science. 2011 Jan 28;331(6016):426-9. doi: 10.1126/science.1193954.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Evolution and Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. twschoener@ucdavis.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21273479" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biological Evolution ; *Biota ; Ecology ; *Ecosystem ; Selection, Genetic
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 27
    Publication Date: 2012-06-08
    Description: The human-microbial ecosystem plays a variety of important roles in human health and disease. Each person can be viewed as an island-like "patch" of habitat occupied by microbial assemblages formed by the fundamental processes of community ecology: dispersal, local diversification, environmental selection, and ecological drift. Community assembly theory, and metacommunity theory in particular, provides a framework for understanding the ecological dynamics of the human microbiome, such as compositional variability within and between hosts. We explore three core scenarios of human microbiome assembly: development in infants, representing assembly in previously unoccupied habitats; recovery from antibiotics, representing assembly after disturbance; and invasion by pathogens, representing assembly in the context of invasive species. Judicious application of ecological theory may lead to improved strategies for restoring and maintaining the microbiota and the crucial health-associated ecosystem services that it provides.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4208626/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4208626/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Costello, Elizabeth K -- Stagaman, Keaton -- Dethlefsen, Les -- Bohannan, Brendan J M -- Relman, David A -- DP1 OD000964/OD/NIH HHS/ -- DP1OD000964/OD/NIH HHS/ -- R01 GM095385/GM/NIGMS NIH HHS/ -- R01 OD011116/OD/NIH HHS/ -- R01GM095385/GM/NIGMS NIH HHS/ -- T32 GM007413/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2012 Jun 8;336(6086):1255-62. doi: 10.1126/science.1224203. Epub 2012 Jun 6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22674335" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Anti-Bacterial Agents/pharmacology/*therapeutic use ; Bacterial Infections/*microbiology ; Biodiversity ; Ecology ; *Ecosystem ; Gastrointestinal Tract/*microbiology ; *Host-Pathogen Interactions ; Humans ; Infant, Newborn ; *Metagenome ; Selection, Genetic ; Symbiosis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 28
    Publication Date: 2013-08-03
    Description: Terrestrial ecosystems have encountered substantial warming over the past century, with temperatures increasing about twice as rapidly over land as over the oceans. Here, we review the likelihood of continued changes in terrestrial climate, including analyses of the Coupled Model Intercomparison Project global climate model ensemble. Inertia toward continued emissions creates potential 21st-century global warming that is comparable in magnitude to that of the largest global changes in the past 65 million years but is orders of magnitude more rapid. The rate of warming implies a velocity of climate change and required range shifts of up to several kilometers per year, raising the prospect of daunting challenges for ecosystems, especially in the context of extensive land use and degradation, changes in frequency and severity of extreme events, and interactions with other stresses.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Diffenbaugh, Noah S -- Field, Christopher B -- New York, N.Y. -- Science. 2013 Aug 2;341(6145):486-92. doi: 10.1126/science.1237123.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305, USA. diffenbaugh@stanford.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23908225" target="_blank"〉PubMed〈/a〉
    Keywords: *Climate Change ; Ecology ; *Ecosystem ; Forecasting ; Global Warming ; Humans ; Models, Theoretical ; Temperature
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 29
    Publication Date: 2014-07-06
    Description: Integration of evidence over the past decade has revised understandings about the major adaptations underlying the origin and early evolution of the genus Homo. Many features associated with Homo sapiens, including our large linear bodies, elongated hind limbs, large energy-expensive brains, reduced sexual dimorphism, increased carnivory, and unique life history traits, were once thought to have evolved near the origin of the genus in response to heightened aridity and open habitats in Africa. However, recent analyses of fossil, archaeological, and environmental data indicate that such traits did not arise as a single package. Instead, some arose substantially earlier and some later than previously thought. From ~2.5 to 1.5 million years ago, three lineages of early Homo evolved in a context of habitat instability and fragmentation on seasonal, intergenerational, and evolutionary time scales. These contexts gave a selective advantage to traits, such as dietary flexibility and larger body size, that facilitated survival in shifting environments.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Anton, Susan C -- Potts, Richard -- Aiello, Leslie C -- New York, N.Y. -- Science. 2014 Jul 4;345(6192):1236828. doi: 10.1126/science.1236828.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for the Study of Human Origins, Department of Anthropology, New York University, Rufus D. Smith Hall, 25 Waverly Place, New York, NY 10003, USA. E-mail: susan.anton@nyu.edu. ; Human Origins Program, National Museum of Natural History, Smithsonian Institution, Post Office Box 37012, Washington, DC 20013-7012, USA. E-mail: pottsr@si.edu. ; Wenner-Gren Foundation, 470 Park Avenue South, 8th Floor, New York, NY 10016, USA. E-mail: laiello@wennergren.org.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24994657" target="_blank"〉PubMed〈/a〉
    Keywords: *Adaptation, Biological ; Animals ; Behavior ; *Biological Evolution ; Body Size ; Brain/anatomy & histology/growth & development ; Climate Change ; Cognition ; Diet ; Ecology ; *Hominidae/anatomy & histology/genetics/growth & development ; Humans ; Organ Size ; Skull/anatomy & histology ; Tooth/anatomy & histology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 30
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    Nature Publishing Group (NPG)
    Publication Date: 2014-07-25
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gewin, Virginia -- England -- Nature. 2014 Jul 24;511(7510):402-4. doi: 10.1038/511402a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25056046" target="_blank"〉PubMed〈/a〉
    Keywords: *Administrative Personnel ; California ; China ; *Consensus ; Ecology ; *Environmental Policy ; Global Warming/*prevention & control/statistics & numerical data ; International Cooperation ; Paleontology ; *Policy Making ; *Politics ; Public Opinion ; *Research Personnel
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 31
    Publication Date: 2018-06-06
    Description: One of the greatest challenges when developing propulsion systems is predicting the interacting effects between the fluid loads, thermal loads, and structural deflection. The interactions between technical disciplines often are not fully analyzed, and the analysis in one discipline often uses a simplified representation of other disciplines as an input or boundary condition. For example, the fluid forces in an engine generate static and dynamic rotor deflection, but the forces themselves are dependent on the rotor position and its orbit. It is important to consider the interaction between the physical phenomena where the outcome of each analysis is heavily dependent on the inputs (e.g., changes in flow due to deflection, changes in deflection due to fluid forces). A rigid design process also lacks the flexibility to employ multiple levels of fidelity in the analysis of each of the components. This project developed and validated an innovative design environment that has the flexibility to simultaneously analyze multiple disciplines and multiple components with multiple levels of model fidelity. Using NASA's open-source multidisciplinary design analysis and optimization (OpenMDAO) framework, this multifaceted system will provide substantially superior capabilities to current design tools.
    Keywords: Aircraft Propulsion and Power
    Type: An Overview of SBIR Phase 2 Airbreathing Propulsion Technologies; 14; NASA/TM-2014-218497
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  • 32
    Publication Date: 2019-06-28
    Description: A comparison of the operating characteristics of 75-millimeter-bore (size 215) cylindrical-roller one-piece inner-race-riding cage-type bearings was made using a laboratory test rig and a turbojet engine. Cooling correlation parameters were determined by means of dimensional analysis, and the generalized results for both the inner- and outer-race bearing operating temperatures are compared for the laboratory test rig and the turbojet engine. Inner- and outer-race cooling-correlation curves were obtained for the turbojet-engine turbine-roller bearing with the same inner- and outer-race correlation parameters and exponents as those determined for the laboratory test-rig bearing. The inner- and outer-race turbine roller-bearing temperatures may be predicted from a single curve, regardless of variations in speed, load, oil flow, oil inlet temperature, oil inlet viscosity, oil-jet diameter or any combination of these parameters. The turbojet-engine turbine-roller-bearing inner-race temperatures were 30 to 60 F greater than the outer-race-maximum temperatures, the exact values depending on the operating condition and oil viscosity; these results are in contrast to the laboratory test-rig results where the inner-race temperatures were less than the outer-race-maximum temperatures. The turbojet-engine turbine-roller bearing, maximum outer-race circumferential temperature variation was approximately 30 F for each of the oils used. The effect of oil viscosity on inner- and outer-race turbojet-engine turbine-roller-bearing temperatures was found to be significant. With the lower viscosity oil (6x10(exp -7) reyns (4.9 centistokes) at 100 F; viscosity index, 83), the inner-race temperature was approximately 30 to 35 F less than with the higher viscosity oil (53x10(exp -7) reyns (42.8 centistokes) at 100 F; viscosity index, 150); whereas the outer-race-maximum temperatures were 12 to 28 F lower with the lower viscosity oil over the DN range investigated.
    Keywords: Aircraft Propulsion and Power
    Type: NACA-RM-E51I05
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  • 33
    Publication Date: 2019-06-28
    Description: A literature survey was conducted to determine the relation between aircraft ignition sources and inflammables. Available literature applicable to the problem of aircraft fire hazards is analyzed and, discussed herein. Data pertaining to the effect of many variables on ignition temperatures, minimum ignition pressures, and minimum spark-ignition energies of inflammables, quenching distances of electrode configurations, and size of openings incapable of flame propagation are presented and discussed. The ignition temperatures and the limits of inflammability of gasoline in air in different test environments, and the minimum ignition pressure and the minimum size of openings for flame propagation of gasoline - air mixtures are included. Inerting of gasoline - air mixtures is discussed.
    Keywords: Aircraft Propulsion and Power
    Type: NACA-TN-2227
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  • 34
    Publication Date: 2019-06-28
    Description: Tests of two propellers having two blades and differing only in the inboard pitch distribution were made in the Langley 8-foot highspeed tunnel to determine the effect of inboard pitch distribution on propeller performance. propeller was designed for operation in the reduced velocity region ahead of an NACA cowling; the inboard pitch distribution of the modified propeller was increased for operation at or near free-stream velocities, such as would be obtained in a pusher installation. conditions covering climb, cruise, and high-speed operation. Wake surveys were taken behind the propellers in order to determine the distribution of thrust along the blades and to aid in the analysis of the results. Test results showed that the modified propeller was about 2.5 percent less efficient for a typical climb condition at all altitudes, 2 percent more efficient for one cruise condition, and 5 percent more efficient for high-speed operation. speed condition, the modified propeller showed a 6-percent loss in efficiency due to compressibility; whereas the original propeller showed an 11-percent efficiency loss due to compressiblity. The lower compressibility loss for the modified propeller resulted from the fact that the inboard sections of this propeller could operate at increased thrust loading after compressibility losses had occurred at the outboard sections.
    Keywords: Aircraft Propulsion and Power
    Type: NACA-TN-2268
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  • 35
    Publication Date: 2019-06-28
    Description: As part of a general investigation of propellers at high forward speeds, tests of two 2-blade propellers having the NACA 4-(3)(8)-03 and NACA 4-(3)(8)-45 blade designs have been made in the Langley 8-foot high-speed tunnel through a range of blade angle from 20 degrees to 60 degrees for forward Mach numbers from 0.165 to 0.725 to establish in detail the changes in propeller characteristics due to compressibility effects. These propellers differed primarily only in blade solidity, one propeller having 50 percent and more solidity than the other. Serious losses in propeller efficiency were found as the propeller tip Mach number exceeded 0.91, irrespective of forward speed or blade angle. The magnitude of the efficiency losses varied from 9 percent to 22 percent per 0.1 increase in tip Mach number above the critical value. The range of advance ratio for peak efficiency decreased markedly with increase of forward speed. The general form of the changes in thrust and power coefficients was found to be similar to the changes in airfoil lift coefficient with changes in Mach number. Efficiency losses due to compressibility effects decreased with increase of blade width. The results indicated that the high level of propeller efficiency obtained at low speeds could be maintained to forward sea-level speeds exceeding 500 miles per hour.
    Keywords: Aircraft Propulsion and Power
    Type: NACA-TR-999
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  • 36
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2019-06-28
    Description: An investigation has been made to explore the possibilities of axial-flow compressors operating with supersonic velocities into the blade rows. Preliminary calculations showed that very high pressure ratios across a stage, together with somewhat increased mass flows, were apparently possible with compressors which decelerated air through the speed of sound in their blading. The first phase of the investigation was the development of efficient supersonic diffusers to decelerate air through the speed of sound. The present report is largely a general discussion of some of the essential aerodynamics of single-stage supersonic axial-flow compressors. As an approach to the study of supersonic compressors, three possible velocity diagrams are discussed briefly. Because of the encouraging results of this study, an experimental single-stage supersonic compressor has been constructed and tested in Freon-12. In this compressor, air decelerates through the speed of sound in the rotor blading and enters the stators at subsonic speeds. A pressure ratio of about 1.8 at an efficiency of about 80 percent has been obtained.
    Keywords: Aircraft Propulsion and Power
    Type: NACA-TR-974 , NACA-ACR-L6D02 , NACA-AR-36
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  • 37
    Publication Date: 2019-06-27
    Description: Sound pressure levels, frequency spectrum, and jet velocity profiles are presented for an engine-afterburner combination at various values of afterburner fuel - air ratio. At the high fuel-air ratios, severe low-frequency resonance was encountered which represented more than half the total energy in the sound spectrum. At similar thrust conditions, lower sound pressure levels were obtained from a current fighter air craft with a different afterburner configuration. The lower sound pressure levels are attributed to resonance-free afterburner operation and thereby indicate the importance of acoustic considerations in afterburner design.
    Keywords: Aircraft Propulsion and Power
    Type: NACA-RM-E54G07
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  • 38
    Publication Date: 2019-07-27
    Description: Enhanced engine operation--operation that is beyond normal limits--has the potential to improve the adaptability and safety of aircraft in emergency situations. Intelligent use of enhanced engine operation to improve the handling qualities of the aircraft requires sophisticated risk estimation techniques and a risk management system that spans the flight and propulsion controllers. In this paper, an architecture that weighs the risks of the emergency and of possible engine performance enhancements to reduce overall risk to the aircraft is described. Two examples of emergency situations are presented to demonstrate the interaction between the flight and propulsion controllers to facilitate the enhanced operation.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2011-217143 , AIAA Paper 2011-1568 , E-17880 , Infotech at Aerospace 2011 Conference; 29-31 Mr. 2011; St. Louis, MO; United States
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  • 39
    Publication Date: 2019-07-27
    Description: A harmonic balance (HB) aeroelastic analysis, which has been recently developed, was used to determine the aeroelastic stability (flutter) characteristics of an experimental fan. To assess the numerical accuracy of this HB aeroelastic analysis, a time-domain aeroelastic analysis was also used to determine the aeroelastic stability characteristics of the same fan. Both of these three-dimensional analysis codes model the unsteady flowfield due to blade vibrations using the Reynolds-averaged Navier-Stokes (RANS) equations. In the HB analysis, the unsteady flow equations are converted to a HB form and solved using a pseudo-time marching method. In the time-domain analysis, the unsteady flow equations are solved using an implicit time-marching approach. Steady and unsteady computations for two vibration modes were carried out at two rotational speeds: 100 percent (design) and 70 percent (part-speed). The steady and unsteady results obtained from the two analysis methods compare well, thus verifying the recently developed HB aeroelastic analysis. Based on the results, the experimental fan was found to have no aeroelastic instability (flutter) at the conditions examined in this study.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2010-216222 , IFASD-2009-101 , E-17203 , International Forum on Aeroelasticity and Structural Dynamics (IFASD 2009); 21?25 Jun. 2009; Seattle, WA
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  • 40
    Publication Date: 2019-07-13
    Description: Computational and experimental analyses of a PICS-Pilot-In-Can-Swirler technology injector, developed by United Technologies Research Center (UTRC) are presented. NASA has defined technology targets for near term (called "N+1", circa 2015), midterm ("N+2", circa 2020) and far term ("N+3", circa 2030) that specify realistic emissions and fuel efficiency goals for commercial aircraft. This injector has potential for application in an engine to meet the Pratt & Whitney N+3 supersonic cycle goals, or the subsonic N+2 engine cycle goals. Experimental methods were employed to investigate supersonic cruise points as well as select points of the subsonic cycle engine; cruise, approach, and idle with a slightly elevated inlet pressure. Experiments at NASA employed gas analysis and a suite of laser-based measurement techniques to characterize the combustor flow downstream from the PICS dump plane. Optical diagnostics employed for this work included Planar Laser-Induced Fluorescence of fuel for injector spray pattern and Spontaneous Raman Spectroscopy for relative species concentration of fuel and CO2. The work reported here used unheated (liquid) Jet-A fuel for all fuel circuits and cycle conditions. The initial tests performed by UTRC used vaporized Jet-A to simulate the expected supersonic cruise condition, which anticipated using fuel as a heat sink. Using the National Combustion Code a PICS-based combustor was modeled with liquid fuel at the supersonic cruise condition. All CFD models used a cubic non-linear k-epsilon turbulence wall functions model, and a semi-detailed Jet-A kinetic mechanism based on a surrogate fuel mixture. Two initial spray droplet size distribution and spray cone conditions were used: 1) an initial condition (Lefebvre) with an assumed Rosin-Rammler distribution, and 7 degree Solid Spray Cone; and 2) the Boundary Layer Stripping (BLS) primary atomization model giving the spray size distribution and directional properties. Contour and line plots are shown in comparison with experimental data (where this data is available) for flow velocities, fuel, and temperature distribution. The CFD results are consistent with experimental observations for fuel distribution and vaporization. Analysis of gas sample results, using a previously-developed NASA NOx correlation, indicates that for sea-level takeoff, the PICS configuration is predicted to deliver an EINOx value of about 3 for the targeted supersonic aircraft. Emissions results at supersonic cruise conditions show potential for meeting the NASA goals with liquid fuel.
    Keywords: Aircraft Propulsion and Power
    Type: E-18953 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 41
    Publication Date: 2019-07-13
    Description: This paper summarizes the procedures of inserting a thin-layer mesh to existing inviscid polyhedral mesh either with or without hanging-node elements as well as presents sample results from its applications to the numerical solution of a single-element LDI combustor using a releasable edition of the National Combustion Code (NCC).
    Keywords: Aircraft Propulsion and Power
    Type: E-18839-1 , AIAA SciTech 2014; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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  • 42
    Publication Date: 2019-07-13
    Description: This lecture will provide an overview of the aircraft turbine engine control research at NASA (National Aeronautics and Space Administration) Glenn Research Center (GRC). A brief introduction to the engine control problem is first provided with a description of the current state-of-the-art control law structure. A historical aspect of engine control development since the 1940s is then provided with a special emphasis on the contributions of GRC. The traditional engine control problem has been to provide a means to safely transition the engine from one steady-state operating point to another based on the pilot throttle inputs. With the increased emphasis on aircraft safety, enhanced performance and affordability, and the need to reduce the environmental impact of aircraft, there are many new challenges being faced by the designers of aircraft propulsion systems. The Controls and Dynamics Branch (CDB) at GRC is leading and participating in various projects in partnership with other organizations within GRC and across NASA, other government agencies, the U.S. aerospace industry, and academia to develop advanced propulsion controls and diagnostics technologies that will help meet the challenging goals of NASA programs under the Aeronautics Research Mission. The second part of the lecture provides an overview of the various CDB technology development activities in aircraft engine control and diagnostics, both current and some accomplished in the recent past. The motivation for each of the research efforts, the research approach, technical challenges and the key progress to date are summarized. The technologies to be discussed include system level engine control concepts, gas path diagnostics, active component control, and distributed engine control architecture. The lecture will end with a futuristic perspective of how the various current technology developments will lead to an Intelligent and Autonomous Propulsion System requiring none to very minimum pilot interface, interfacing directly with the flight management system to determine its mode of operation, and providing personalized engine control to optimize its performance given the current condition and mission objectives.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN17532 , SAE 2014 Aerospace Systems and Technology Conference; Sep 23, 2014 - Sep 25, 2014; Cincinnati, OH; United States
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  • 43
    Publication Date: 2019-07-13
    Description: Future civil transport designs may incorporate engine inlets integrated into the body of the aircraft to take advantage of efficiency increases due to weight and drag reduction. Additional increases in engine efficiency are predicted if the inlet ingests the lower momentum boundary layer flow. Previous studies have shown, however, that efficiency benefits of Boundary Layer Ingesting (BLI) ingestion are very sensitive to the magnitude of fan and duct losses, and blade structural response to the non-uniform flow field that results from a BLI inlet has not been studied in-depth. This paper presents an effort to extend the modeling capabilities of an existing rotating turbomachinery unsteady analysis code to include the ability to solve the external and internal flow fields of a BLI inlet. The TURBO code has been a successful tool in evaluating fan response to flow distortions for traditional engine/inlet integrations, such as the development of rotating stall and inlet distortion through compressor stages. This paper describes the first phase of an effort to extend the TURBO model to calculate the external and inlet flowfield upstream of fan so that accurate pressure distortions that result from BLI configurations can be computed and used to analyze fan aerodynamics and structural response. To validate the TURBO program modifications for the BLI flowfield, experimental test data obtained by NASA for a flushmounted S-duct with large amounts of boundary layer ingestion was modeled. Results for the flow upstream and in the inlet are presented and compared to experimental data for several high Reynolds number flows to validate the modifications to the solver. Quantitative data is presented that indicates good predictive capability of the model in the upstream flow. A representative fan is attached to the inlet and results are presented for the coupled inlet/fan model. The impact on the total pressure distortion at the AIP after the fan is attached is examined.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN15952 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, Ohio; United States
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  • 44
    Publication Date: 2019-07-13
    Description: This paper presents a model-based architecture for performance trend monitoring and gas path fault diagnostics designed for analyzing streaming transient aircraft engine measurement data. The technique analyzes residuals between sensed engine outputs and model predicted outputs for fault detection and isolation purposes. Diagnostic results from the application of the approach to test data acquired from an aircraft turbofan engine are presented. The approach is found to avoid false alarms when presented nominal fault-free data. Additionally, the approach is found to successfully detect and isolate gas path seeded-faults under steady-state operating scenarios although some fault misclassifications are noted during engine transients. Recommendations for follow-on maturation and evaluation of the technique are also presented.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16186 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 45
    Publication Date: 2019-07-13
    Description: Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn for future generations of commercial aircraft, but these systems must be designed to overcome the challenge of high dynamic stresses in fan blades due to forced response. High dynamic stresses can lead to high cycle fatigue failures. High-fidelity computational analysis of the fan aeromechanics is integral to an ongoing effort to design a boundary layer ingesting inlet and fan for a wind-tunnel test. An unsteady flow solution from a Reynoldsaveraged Navier Stokes analysis of a coupled inlet-fan system is used to calculate blade unsteady loading and assess forced response of the fan to distorted inflow. Conducted prior to the mechanical design of a fan, the initial forced response analyses performed in this study provide an early look at the levels of dynamic stresses that are likely to be encountered. For the boundary layer ingesting inlet, the distortion contains strong engine order excitations that act simultaneously. The combined effect of these harmonics was considered in the calculation of the forced response stresses. Together, static and dynamic stresses can provide the information necessary to evaluate whether the blades are likely to fail due to high cycle fatigue. Based on the analyses done, the overspeed condition is likely to result in the smallest stress margin in terms of the mean and alternating stresses. Additional work is ongoing to expand the analyses to off-design conditions, on-resonance conditions, and to include more detailed modeling of the blade structure.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN15948 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 46
    Publication Date: 2019-07-13
    Description: This presentation contains Wind-US results presented at the 2nd Propulsion Aerodynamics Workshop. The workshop was organized by the American Institute of Aeronautics and Astronautics, Air Breathing Propulsion Systems Integration Technical Committee with the purpose of assessing the accuracy of computational fluid dynamics for air breathing propulsion applications. Attendees included representatives from government, industry, academia, and commercial software companies. Participants were encouraged to explore and discuss all aspects of the simulation process including the effects of mesh type and refinement, solver numerical schemes, and turbulence modeling. The first set of challenge cases involved computing the thrust and discharge coefficients for a 25deg conical nozzle for a range of nozzle pressure ratios between 1.4 and 7.0. Participants were also asked to simulate two cases in which the 25deg conical nozzle was bifurcated by a solid plate, resulting in vortex shedding (NPR=1.6) and shifted plume shock (NPR=4.0). A second set of nozzle cases involved computing the discharge and thrust coefficients for a convergent dual stream nozzle for a range of subsonic nozzle pressure ratios. The workshop committee also compared the plume mixing of these cases across various codes and models. The final test case was a serpentine inlet diffuser with an outlet to inlet area ratio of 1.52 and an offset of 1.34 times the inlet diameter. Boundary layer profiles, wall static pressure, and total pressure at downstream rake locations were examined.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16809 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States|AIAA Propulsion Aerodynamics Workshop; Jul 31, 2014 - Aug 01, 2014; Cleveland, OH; United States
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  • 47
    Publication Date: 2019-07-13
    Description: This paper presents a model-based architecture for performance trend monitoring and gas path fault diagnostics designed for analyzing streaming transient aircraft engine measurement data. The technique analyzes residuals between sensed engine outputs and model predicted outputs for fault detection and isolation purposes. Diagnostic results from the application of the approach to test data acquired from an aircraft turbofan engine are presented. The approach is found to avoid false alarms when presented nominal fault-free data. Additionally, the approach is found to successfully detect and isolate gas path seeded-faults under steady-state operating scenarios although some fault misclassifications are noted during engine transients. Recommendations for follow-on maturation and evaluation of the technique are also presented.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16658 , 50th Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 48
    Publication Date: 2019-07-13
    Description: Recent calculations of pulse-combustors operating at high-pressure conditions produced pressure gains significantly lower than those observed experimentally and computationally at atmospheric conditions. The factors limiting the pressure-gain at high-pressure conditions are identified, and the effects of fuel injection and air mixing characteristics on performance are investigated. New pulse-combustor configurations were developed, and the results show that by suitable changes to the combustor geometry, fuel injection scheme and valve dynamics the performance of the pulse-combustor operating at high-pressure conditions can be increased to levels comparable to those observed at atmospheric conditions. In addition, the new configurations can significantly reduce the levels of NOx emissions. One particular configuration resulted in extremely low levels of NO, producing an emission index much less than one, although at a lower pressure-gain. Calculations at representative cruise conditions demonstrated that pulse-combustors can achieve a high level of performance at such conditions.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16221 , Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, Ohio; United States
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  • 49
    Publication Date: 2019-07-13
    Description: A summary of the propulsion system modeling under NASA's High Speed Project (HSP) AeroPropulsoServoElasticity (APSE) task is provided with a focus on the propulsion system for the lowboom supersonic configuration developed by Lockheed Martin and referred to as the N+2 configuration. This summary includes details on the effort to date to develop computational models for the various propulsion system components. The objective of this paper is to summarize the model development effort in this task, while providing more detail in the modeling areas that have not been previously published. The purpose of the propulsion system modeling and the overall APSE effort is to develop an integrated dynamic vehicle model to conduct appropriate unsteady analysis of supersonic vehicle performance. This integrated APSE system model concept includes the propulsion system model, and the vehicle structural-aerodynamics model. The development to date of such a preliminary integrated model will also be summarized in this report.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16343 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 50
    Publication Date: 2019-07-13
    Description: Distributed Engine Control (DEC) is an enabling technology that has the potential to advance the state-of-the-art in gas turbine engine control. To analyze the capabilities that DEC offers, a Hardware-In-the-Loop (HIL) test bed is being developed at NASA Glenn Research Center. This test bed will support a systems-level analysis of control capabilities in closed-loop engine simulations. The structure of the HIL emulates a virtual test cell by implementing the operator functions, control system, and engine on three separate computers. This implementation increases the flexibility and extensibility of the HIL. Here, a method is discussed for implementing these interfaces by connecting the three platforms over a dedicated Local Area Network (LAN). This approach is verified using the Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k), which is typically implemented on one computer. There are marginal differences between the results from simulation of the typical and the three-computer implementation. Additional analysis of the LAN network, including characterization of network load, packet drop, and latency, is presented. The three-computer setup supports the incorporation of complex control models and proprietary engine models into the HIL framework.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16304 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 51
    Publication Date: 2019-07-13
    Description: This paper covers the development of an integrated nonlinear dynamic simulation for a variable cycle turbofan engine and nozzle that can be integrated with an overall vehicle Aero-Propulso-Servo-Elastic (APSE) model. A previously developed variable cycle turbofan engine model is used for this study and is enhanced here to include variable guide vanes allowing for operation across the supersonic flight regime. The primary focus of this study is to improve the fidelity of the model's thrust response by replacing the simple choked flow equation convergent-divergent nozzle model with a MacCormack method based quasi-1D model. The dynamic response of the nozzle model using the MacCormack method is verified by comparing it against a model of the nozzle using the conservation element/solution element method. A methodology is also presented for the integration of the MacCormack nozzle model with the variable cycle engine.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16231 , Propulsion and Energy Forum 2014; Jul 28, 2014 - Jul 30, 2014; Cleveland, Ohio; United States
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  • 52
    Publication Date: 2019-07-13
    Description: NASA's Rotary Wing Project is investigating technologies that will enable the development of revolutionary civil tilt rotor aircraft. Previous studies have shown that for large tilt rotor aircraft to be viable, the rotor speeds need to be slowed significantly during the cruise portion of the flight. This requirement to slow the rotors during cruise presents an interesting challenge to the propulsion system designer as efficient engine performance must be achieved at two drastically different operating conditions. One potential solution to this challenge is to use a transmission with multiple gear ratios and shift to the appropriate ratio during flight. This solution will require a large transmission that is likely to be maintenance intensive and will require a complex shifting procedure to maintain power to the rotors at all times. An alternative solution is to use a fixed gear ratio transmission and require the power turbine to operate efficiently over the entire speed range. This concept is referred to as a variable-speed power-turbine (VSPT) and is the focus of the current study. This paper explores the design of a variable speed power turbine for civil tilt rotor applications using design optimization techniques applied to NASA's new meanline tool, the Object-Oriented Turbomachinery Analysis Code (OTAC).
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16310 , Propulsion and Energy 2014; Jul 28, 2014 - Jul 30, 2014; Cleveland, Ohio; United States
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  • 53
    Publication Date: 2019-07-13
    Description: The Toolbox for Modeling and Analysis of Thermodynamic Systems (T-MATS) is a tool that has been developed to allow a user to build custom models of systems governed by thermodynamic principles using a template to model each basic process. Validation of this tool in an engine model application was performed through reconstruction of the Commercial Modular Aero-Propulsion System Simulation (C-MAPSS) (v2) using the building blocks from the T-MATS (v1) library. In order to match the two engine models, it was necessary to address differences in several assumptions made in the two modeling approaches. After these modifications were made, validation of the engine model continued by integrating both a steady-state and dynamic iterative solver with the engine plant and comparing results from steady-state and transient simulation of the T-MATS and C-MAPSS models. The results show that the T-MATS engine model was accurate within 3 of the C-MAPSS model, with inaccuracy attributed to the increased dimension of the iterative solver solution space required by the engine model constructed using the T-MATS library. This demonstrates that, given an understanding of the modeling assumptions made in T-MATS and a baseline model, the T-MATS tool provides a viable option for constructing a computational model of a twin-spool turbofan engine that may be used in simulation studies.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN16276 , Propulsion and Energy Forum 2014; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 54
    Publication Date: 2019-07-13
    Description: These presentations cover some of the ongoing work in dynamic modeling and dynamic systems analysis. The first presentation discusses dynamic systems analysis and how to integrate dynamic performance information into the systems analysis. The ability to evaluate the dynamic performance of an engine design may allow tradeoffs between the dynamic performance and operability of a design resulting in a more efficient engine design. The second presentation discusses the Toolbox for Modeling and Analysis of Thermodynamic Systems (T-MATS). T-MATS is a Simulation system with a library containing the basic building blocks that can be used to create dynamic Thermodynamic Systems. Some of the key features include Turbo machinery components, such as turbines, compressors, etc., and basic control system blocks. T-MAT is written in the Matlab-Simulink environment and is open source software. The third presentation focuses on getting additional performance from the engine by allowing the limit regulators only to be active when a limit is danger of being violated. Typical aircraft engine control architecture is based on MINMAX scheme, which is designed to keep engine operating within prescribed mechanical/operational safety limits. Using a conditionally active min-max limit regulator scheme, additional performance can be gained by disabling non-relevant limit regulators
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN12088 , Propulsion, Control, and Diagnostic Workshop; Dec 11, 2013 - Dec 12, 2013; Cleveland, OH; United States
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  • 55
    Publication Date: 2019-07-13
    Description: A two-dimensional, computational fluid dynamic (CFD) simulation of a semi-idealized rotating detonation engine (RDE) is described. The simulation operates in the detonation frame of reference and utilizes a relatively coarse grid such that only the essential primary flow field structure is captured. This construction yields rapidly converging, steady solutions. Results from the simulation are compared to those from a more complex and refined code, and found to be in reasonable agreement. The performance impacts of several RDE design parameters are then examined. Finally, for a particular RDE configuration, it is found that direct performance comparison can be made with a straight-tube pulse detonation engine (PDE). Results show that they are essentially equivalent.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2014-216634 , AIAA Paper 2014-0284 , E-18837 , GRC-E-DAA-TN12556 , Science and Technology Forum and Exposition (SciTech2014):; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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  • 56
    Publication Date: 2019-07-13
    Description: The NASA Environmentally Responsible Aviation (ERA) Project is focused on developing and demonstrating integrated systems technologies to TRL 4-6 by 2020 that enable reduced fuel burn, emissions, and noise for futuristic air vehicles. The specific goals aim to simultaneously reduce fuel burn by 50%, reduce Landing and Take-off Nitrous Oxides emissions by 75% relative to the CAEP 6 guidelines, and reduce cumulative noise by 42 Decibels relative to the Stage 4 guidelines. These goals apply to the integrated vehicle and propulsion system and are based on a reference mission of 3000nm flight of a Boeing 777-200 with GE90 engines. This paper will focus primarily on the ERA propulsion technology portfolio, which consists of advanced combustion, propulsor, and core technologies to enable these integrated air vehicle systems goals. An overview of the ERA propulsion technologies will be described and the status and results to date will be presented.
    Keywords: Aircraft Propulsion and Power
    Type: E-18625 , GRC-E-DAA-TN5670 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 29, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 57
    Publication Date: 2019-07-13
    Description: Advances in electric machine efficiency and energy storage capability are enabling a new alternative to traditional propulsion systems for aircraft. This has already begun with several small concept and demonstration vehicles, and NASA projects this technology will be essential to meet energy and emissions goals for commercial aviation in the next 30 years. In order to raise the Technology Readiness Level of electric propulsion systems, practical integration and performance challenges will need to be identified and studied in the near-term so that larger, more advanced electric propulsion system testbeds can be designed and built. Researchers at NASA Armstrong Flight Research Center are building up a suite of test articles for the development, integration, and validation of these systems in a real world environment.
    Keywords: Aircraft Propulsion and Power
    Type: AFRC-E-DAA-TN15761 , AIAA Aviation Technology, Integration, and Operations Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta GA; United States
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  • 58
    Publication Date: 2019-07-13
    Description: The objective of this paper is to describe an accurate and efficient reduced order modeling method for aeroelastic (AE) analysis and for determining the flutter boundary. Without losing accuracy, we develop a reduced order model based on the Volterra series to achieve significant savings in computational cost. The aerodynamic force is provided by a high-fidelity solution from the Reynolds-averaged Navier-Stokes (RANS) equations; the structural mode shapes are determined from the finite element analysis. The fluid-structure coupling is then modeled by the state-space formulation with the structural displacement as input and the aerodynamic force as output, which in turn acts as an external force to the aeroelastic displacement equation for providing the structural deformation. NASA's rotor 67 blade is used to study its aeroelastic characteristics under the designated operating condition. First, the CFD results are validated against measured data available for the steady state condition. Then, the accuracy of the developed reduced order model is compared with the full-order solutions. Finally the aeroelastic solutions of the blade are computed and a flutter boundary is identified, suggesting that the rotor, with the material property chosen for the study, is structurally stable at the operating condition, free of encountering flutter.
    Keywords: Aircraft Propulsion and Power
    Type: GT2014-25474 , GRC-E-DAA-TN13691 , ASME Turbo Expo 2014; Jun 16, 2014 - Jun 20, 2014; Dusseldorf; Germany
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  • 59
    Publication Date: 2019-07-13
    Description: Centrifugal compressors are compatible with the low exit corrected flows found in the high pressure compressor of turboshaft engines and may play an increasing role in turbofan engines as engine overall pressure ratios increase. Centrifugal compressor stages are difficult to model accurately with RANS CFD solvers. A computational study of the CC3 centrifugal impeller in its vaneless diffuser configuration was undertaken as part of an effort to understand potential causes of RANS CFD mis-prediction in these types of geometries. Three steady, periodic cases of the impeller and diffuser were modeled using the TURBO Parallel Version 4 code: (1) a k- turbulence model computation on a 6.8 million point grid using wall functions, (2) a k- turbulence model computation on a 14 million point grid integrating to the wall, and (3) a k- turbulence model computation on the 14 million point grid integrating to the wall. It was found that all three cases compared favorably to data from inlet to impeller trailing edge, but the k- and k- computations had disparate results beyond the trailing edge and into the vaneless diffuser. A large region of reversed flow was observed in the k- computations which extended from 70 to 100 percent span at the exit rating plane, whereas the k- computation had reversed flow from 95 to 100 percent span. Compared to experimental data at near-peak-efficiency, the reversed flow region in the k- case resulted in an underprediction in adiabatic efficiency of 8.3 points, whereas the k- case was 1.2 points lower in efficiency.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-216566 , AIAA Paper 2013-3631 , E-18754 , GRC-E-DAA-TN9986 , Joint Propulsion Conference and Exhibit; Jul 14, 2013 - Jul 17, 2013; San Jose, CA; United States
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  • 60
    Publication Date: 2019-07-13
    Description: Centrifugal compressors are compatible with the low exit corrected flows found in the high pressure compressor of turboshaft engines and may play an increasing role in turbofan engines as engine overall pressure ratios increase. Centrifugal compressor stages are difficult to model accurately with RANS CFD solvers. A computational study of the CC3 centrifugal impeller in its vaneless diffuser configuration was undertaken as part of an effort to understand potential causes of RANS CFD mis-prediction in these types of geometries. Three steady, periodic cases of the impeller and diffuser were modeled using the TURBO Parallel Version 4 code: 1) a k-epsilon turbulence model computation on a 6.8 million point grid using wall functions, 2) a k-epsilon turbulence model computation on a 14 million point grid integrating to the wall, and 3) a k-omega turbulence model computation on the 14 million point grid integrating to the wall. It was found that all three cases compared favorably to data from inlet to impeller trailing edge, but the k-epsilon and k-omega computations had disparate results beyond the trailing edge and into the vaneless diffuser. A large region of reversed flow was observed in the k-epsilon computations which extended from 70% to 100% span at the exit rating plane, whereas the k-omega computation had reversed flow from 95% to 100% span. Compared to experimental data at near-peak-efficiency, the reversed flow region in the k-epsilon case resulted in an under-prediction in adiabatic efficiency of 8.3 points, whereas the k-omega case was 1.2 points lower in efficiency.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-216566 , E-18754 , GRC-E-DAA-TN9986 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit; Jul 15, 2013 - Jul 17, 2013; San Jose, CA; United States|International Energy Conversion Engineering Conference; Jul 15, 2013 - Jul 17, 2013; San Jose, CA; United States
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  • 61
    Publication Date: 2019-07-13
    Description: This paper presents an overview of the propulsion research and technology portfolio of NASA Fundamental Aeronautics Program Fixed Wing Project. The research is aimed at significantly reducing the thrust specific fuel/energy consumption of notional advanced fixed wing aircraft (by 60 % relative to a baseline Boeing 737-800 aircraft with CFM56-7B engines) in the 2030-2035 time frame. The research investments described herein are aimed at improving propulsive efficiency through higher bypass ratio fans, improving thermal efficiency through compact high overall pressure ratio gas generators, and exploring the potential benefits of boundary layer ingestion propulsion and hybrid gas-electric propulsion concepts.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-216548 , E-18727 , GRC-E-DAA-TN10096 , International Energy Conversion Engineering Conference; Jul 15, 2013 - Jul 17, 2013; San Jose, CA; United States|AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit; Jul 15, 2013 - Jul 17, 2013; San Jose, CA; United States
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  • 62
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN13570 , NASA Aeronautics Research Mission Directorate (ARMD) 2014 Seedling Fund technical Seminar; Feb 19, 2014 - Feb 27, 2014; Cleveland, OH; United States
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  • 63
    Publication Date: 2019-07-13
    Description: The ability to monitor the structural health of the rotating components, especially in the hot sections of turbine engines, is of major interest to aero community in improving engine safety and reliability. The use of instrumentation for these applications remains very challenging. It requires sensors and techniques that are highly accurate, are able to operate in a high temperature environment, and can detect minute changes and hidden flaws before catastrophic events occur. The National Aeronautics and Space Administration (NASA) has taken a lead role in the investigation of new sensor technologies and techniques for the in situ structural health monitoring of gas turbine engines. As part of this effort, microwave sensor technology has been investigated as a means of making high temperature non-contact blade tip clearance, blade tip timing, and blade vibration measurements for use in gas turbine engines. This paper presents a summary of key results and findings obtained from the evaluation of two different types of microwave sensors that have been investigated for use possible in structural health monitoring applications. The first is a microwave blade tip clearance sensor that has been evaluated on a large scale Axial Vane Fan, a subscale Turbofan, and more recently on sub-scale turbine engine like disks. The second is a novel microwave based blade vibration sensor that was also used in parallel with the microwave blade tip clearance sensors on the experiments with the sub-scale turbine engine disks.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN13685 , SPIE Smart Structures/NDE 2014 Conference; Mar 09, 2014 - Mar 13, 2014; San Diego, CA; United States
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  • 64
    Publication Date: 2019-07-13
    Description: In response to growing aviation demands and concerns about the environment and energy usage, a team at NASA proposed and examined a revolutionary aeropropulsion concept, a turboelectric distributed propulsion system, which employs multiple electric motor-driven propulsors that are distributed on a large transport vehicle. The power to drive these electric propulsors is generated by separately located gas-turbine-driven electric generators on the airframe. This arrangement enables the use of many small-distributed propulsors, allowing a very high effective bypass ratio, while retaining the superior efficiency of large core engines, which are physically separated but connected to the propulsors through electric power lines. Because of the physical separation of propulsors from power generating devices, a new class of vehicles with unprecedented performance employing such revolutionary propulsion system is possible in vehicle design. One such vehicle currently being investigated by NASA is called the "N3-X" that uses a hybrid-wing-body for an airframe and superconducting generators, motors, and transmission lines for its propulsion system. On the N3-X these new degrees of design freedom are used (1) to place two large turboshaft engines driving generators in freestream conditions to minimize total pressure losses and (2) to embed a broad continuous array of 14 motor-driven fans on the upper surface of the aircraft near the trailing edge of the hybrid-wing-body airframe to maximize propulsive efficiency by ingesting thick airframe boundary layer flow. Through a system analysis in engine cycle and weight estimation, it was determined that the N3-X would be able to achieve a reduction of 70% or 72% (depending on the cooling system) in energy usage relative to the reference aircraft, a Boeing 777-200LR. Since the high-power electric system is used in its propulsion system, a study of the electric power distribution system was performed to identify critical dynamic and safety issues. This paper presents some of the features and issues associated with the turboelectric distributed propulsion system and summarizes the recent study results, including the high electric power distribution, in the analysis of the N3-X vehicle.
    Keywords: Aircraft Propulsion and Power
    Type: ISABEý-2013-1719 , E-18689 , 2013 International Society for Air Breathing Engines; Sep 09, 2013 - Sep 13, 2013; Busan; Korea, Republic of
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  • 65
    Publication Date: 2019-07-13
    Description: Turbine engines are highly complex mechanical systems that are becoming increasingly dependent on control technologies to achieve system performance and safety metrics. However, the contribution of controls to these measurable system objectives is difficult to quantify due to a lack of tools capable of informing the decision makers. This shortcoming hinders technology insertion in the engine design process. NASA Glenn Research Center is developing a Hardware-inthe- Loop (HIL) platform and analysis tool set that will serve as a focal point for new control technologies, especially those related to the hardware development and integration of distributed engine control. The HIL platform is intended to enable rapid and detailed evaluation of new engine control applications, from conceptual design through hardware development, in order to quantify their impact on engine systems. This paper discusses the complex interactions of the control system, within the context of the larger engine system, and how new control technologies are changing that paradigm. The conceptual design of the new HIL platform is then described as a primary tool to address those interactions and how it will help feed the insertion of new technologies into future engine systems.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-217883 , E-18694 , ASME Turbo Expo 2013; Jun 03, 2013 - Jun 07, 2013; San Antonio, TX; United States
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  • 66
    Publication Date: 2019-07-13
    Description: CMC research at NASA Glenn is focused on aircraft propulsion applications. The objective is to enable reduced engine emissions and fuel consumption for more environmentally friendly aircraft. Engine system studies show that incorporation of ceramic composites into turbine engines will enable significant reductions in emissions and fuel burn due to increased engine efficiency resulting from reduced cooling requirements for hot section components. This presentation will describe recent progress and challenges in developing fiber and matrix constituents for 2700 F CMC turbine applications. In addition, ongoing research in the development of durable environmental barrier coatings, ceramic joining integration technologies and life prediction methods for CMC engine components will be reviewed.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN9702 , Pacific Rim Conference on Ceramic and Glass; Jun 02, 2013 - Jun 07, 2013; San Diego, CA; United States
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  • 67
    Publication Date: 2019-07-13
    Description: Luminescence-based surface temperature measurements from an ultra-bright Cr-doped GdAlO3 perovskite (GAP:Cr) coating were successfully conducted on an air-film-cooled stator vane doublet exposed to the afterburner flame of a J85 test engine at University of Tennessee Space Institute (UTSI). The objective of the testing at UTSI was to demonstrate that reliable thermal barrier coating (TBC) surface temperatures based on luminescence decay of a thermographic phosphor could be obtained from the surface of an actual engine component in an aggressive afterburner flame environment and to address the challenges of a highly radiant background and high velocity gases. A high-pressure turbine vane doublet from a Honeywell TECH7000 turbine engine was coated with a standard electron-beam physical vapor deposited (EB-PVD) 200-m-thick TBC composed of yttria-stabilized zirconia (YSZ) onto which a 25-m-thick GAP:Cr thermographic phosphor layer was deposited by EB-PVD. The ultra-bright broadband luminescence from the GAP:Cr thermographic phosphor is shown to offer the advantage of over an order-of-magnitude greater emission intensity compared to rare-earth-doped phosphors in the engine test environment. This higher emission intensity was shown to be very desirable for overcoming the necessarily restricted probe light collection solid angle and for achieving high signal-to-background levels. Luminescence-decay-based surface temperature measurements varied from 500 to over 1000C depending on engine operating conditions and level of air film cooling.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN8877 , 59th International Instrumentation Symposium; May 13, 2013 - May 17, 2013; Cleveland, OH; United States
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  • 68
    Publication Date: 2019-07-13
    Description: The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8 percent of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-216525 , E-18686 , GT2013-95049 , GRC-E-DAA-TN7849 , ASME Turbo Expo 2013; Jun 03, 2013 - Jun 07, 2013; San Antonio, TX; United States
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  • 69
    Publication Date: 2019-07-13
    Description: A "seeded fault test" in support of a rotorcraft condition based maintenance program (CBM), is an experiment in which a component is tested with a known fault while health monitoring data is collected. These tests are performed at operating conditions comparable to operating conditions the component would be exposed to while installed on the aircraft. Performance of seeded fault tests is one method used to provide evidence that a Health Usage Monitoring System (HUMS) can replace current maintenance practices required for aircraft airworthiness. Actual in-service experience of the HUMS detecting a component fault is another validation method. This paper will discuss a hybrid validation approach that combines in service-data with seeded fault tests. For this approach, existing in-service HUMS flight data from a naturally occurring component fault will be used to define a component seeded fault test. An example, using spiral bevel gears as the targeted component, will be presented. Since the U.S. Army has begun to develop standards for using seeded fault tests for HUMS validation, the hybrid approach will be mapped to the steps defined within their Aeronautical Design Standard Handbook for CBM. This paper will step through their defined processes, and identify additional steps that may be required when using component test rig fault tests to demonstrate helicopter CI performance. The discussion within this paper will provide the reader with a better appreciation for the challenges faced when defining a seeded fault test for HUMS validation.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM2013-217872 , E-18669 , Joint Machinery Failure Prevention Technology (MFPT) 2013; May 13, 2013 - May 17, 2013; Cleveland, OH; United States|59th International Instrumentation Symposium (IIS); May 13, 2013 - May 17, 2013; Cleveland, OH; United States
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  • 70
    Publication Date: 2019-07-13
    Description: A research team of U.S. Government agencies and engine manufacturers are designing an experiment to test volcanic-ash ingestion by a NASA owned F117 engine that was donated by the U.S. Air Force. The experiment is being conducted under the auspices of NASA s Vehicle Integrated Propulsion Research (VIPR) Program and will take place in early 2014 at Edwards AFB in California as an on-ground, on-wing test. The primary objectives are to determine the effect on the engine of several hours of exposure to low to moderate ash concentrations, currently proposed at 1 and 10 mg/m3 and to evaluate the capability of engine health management technologies for detecting these effects. A natural volcanic ash will be used that is representative of distal ash clouds many 100's to approximately 1000 km from a volcanic source i.e., the ash should be composed of fresh glassy particles a few tens of microns in size. The glassy ash particles are expected to soften and become less viscous when exposed to the high temperatures of the combustion chamber, then stick to the nozzle guide vanes of the high-pressure turbine. Numerous observations and measurements of the engine s performance and degradation will be made during the course of the experiment, including borescope and tear-down inspections. While not intended to be sufficient for rigorous certification of engine performance when ash is ingested, the experiment should provide useful information to aircraft manufacturers, airline operators, and military and civil regulators in their efforts to evaluate the range of risks that ash hazards pose to aviation.
    Keywords: Aircraft Propulsion and Power
    Type: GRC-E-DAA-TN8284 , 6th International Workshop on Volcanic Ash; Mar 11, 2013 - Mar 15, 2013; Citeko; Indonesia
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  • 71
    Publication Date: 2019-07-13
    Description: The objective of this study was to illustrate the importance of combining Health Usage Monitoring Systems (HUMS) data with usage monitoring system data when detecting rotorcraft transmission health. Six gear sets were tested in the NASA Glenn Spiral Bevel Gear Fatigue Rig. Damage was initiated and progressed on the gear and pinion teeth. Damage progression was measured by debris generation and documented with inspection photos at varying torque values. A contact fatigue analysis was applied to the gear design indicating the effect temperature, load and reliability had on gear life. Results of this study illustrated the benefits of combining HUMS data and actual usage data to indicate progression of damage for spiral bevel gears.
    Keywords: Aircraft Propulsion and Power
    Type: E-18665 , American Helicopter Society 69th Annual Forum; May 21, 2013 - May 23, 2013; Phoenix, AZ; United States
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  • 72
    Publication Date: 2019-07-13
    Description: The performance of high-speed helical gear trains is of particular importance for tiltrotor aircraft drive systems. These drive systems are used to provide speed reduction/torque multiplication from the gas turbine output shaft and provide the necessary offset between these parallel shafts in the aircraft. Four different design configurations have been tested in the NASA Glenn Research Center, High Speed Helical Gear Train Test Facility. The design configurations included the current aircraft design, current design with isotropic superfinished gear surfaces, double helical design (inward and outward pumping), increased pitch (finer teeth), and an increased helix angle. All designs were tested at multiple input shaft speeds (up to 15,000 rpm) and applied power (up to 5,000 hp). Also two lubrication, system-related, variables were tested: oil inlet temperature (160 to 250 F) and lubricating jet pressure (60 to 80 psig). Experimental data recorded from these tests included power loss of the helical system under study, the temperature increase of the lubricant from inlet to outlet of the drive system and fling off temperatures (radially and axially). Also, all gear systems were tested with and without shrouds around the gears. The empirical data resulting from this study will be useful to the design of future helical gear train systems anticipated for next generation rotorcraft drive systems.
    Keywords: Aircraft Propulsion and Power
    Type: E-18652 , American Helicopter Society 69th Annual Forum; May 21, 2013 - May 23, 2013; Phoenix, AZ; United States
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  • 73
    Publication Date: 2019-07-13
    Description: This report highlights one of the many successful projects at the NASA Dryden Flight Research Center that was approved for FY12 funding under the Center Innovation Fund. This project was focused on advancing the technology readiness level of one specific type of altitude-compensating nozzle: the dual-bell rocket nozzle. When considering a rocket's performance over its entire integrated trajectory, the dual-bell nozzle has been predicted to achieve a higher total impulse over the conventional bell nozzle, which is expected to result in a greater capability of payload mass to low-Earth orbit. Although the dual-bell rocket nozzle has been thoroughly studied for several decades, this nozzle has still not been adequately tested in a relevant flight-like environment. This report provides highlights and top-level details on the FY12 feasibility effort to advance this promising technology through flight test, a collaborative effort which leverages NASA Marshall's dual-bell nozzle research and development with Dryden's expertise in propulsion-focused flight testing. To accomplish this goal, the NASA F-15B is proposed as the testbed for the initial flight-test campaign to advance this greatly needed capability.
    Keywords: Aircraft Propulsion and Power
    Type: DFRC-E-DAA-TN5973
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  • 74
    Publication Date: 2019-07-13
    Description: An inlet system is being tested to evaluate methodologies for a turbine based combined cycle propulsion system to perform a controlled inlet mode transition. Prior to wind tunnel based hardware testing of controlled mode transitions, simulation models are used to test, debug, and validate potential control algorithms. One candidate simulation package for this purpose is the High Mach Transient Engine Cycle Code (HiTECC). The HiTECC simulation package models the inlet system, propulsion systems, thermal energy, geometry, nozzle, and fuel systems. This paper discusses the modification and redesign of the simulation package and control system to represent the NASA large-scale inlet model for Combined Cycle Engine mode transition studies, mounted in NASA Glenn s 10-foot by 10-foot Supersonic Wind Tunnel. This model will be used for designing and testing candidate control algorithms before implementation.
    Keywords: Aircraft Propulsion and Power
    Type: E-18419-1 , 48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 30, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 75
    Publication Date: 2019-07-13
    Description: This paper describes piloted evaluation of enhanced propulsion control modes for emergency operation of aircraft. Fast Response and Overthrust modes were implemented to assess their ability to help avoid or mitigate potentially catastrophic situations, both on the ground and in flight. Tests were conducted to determine the reduction in takeoff distance achievable using the Overthrust mode. Also, improvements in Dutch roll damping, enabled by using yaw rate feedback to the engines to replace the function of a stuck rudder, were investigated. Finally, pilot workload and ability to handle the impaired aircraft on approach and landing were studied. The results showed that improvement in all aspects is possible with these enhanced propulsion control modes, but the way in which they are initiated and incorporated is important for pilot comfort and perceived benefit.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217698 , AIAA Paper 2012-2604 , E-18385 , AIAA Infotech@Aerospace Conference; Jun 19, 2012 - Jun 21, 2012; Garden Grove, CA; United States
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  • 76
    Publication Date: 2019-07-13
    Description: An inlet system is being tested to evaluate methodologies for a turbine based combined cycle propulsion system to perform a controlled inlet mode transition. Prior to wind tunnel based hardware testing of controlled mode transitions, simulation models are used to test, debug, and validate potential control algorithms. One candidate simulation package for this purpose is the High Mach Transient Engine Cycle Code (HiTECC). The HiTECC simulation package models the inlet system, propulsion systems, thermal energy, geometry, nozzle, and fuel systems. This paper discusses the modification and redesign of the simulation package and control system to represent the NASA large-scale inlet model for Combined Cycle Engine mode transition studies, mounted in NASA Glenn s 10- by 10-Foot Supersonic Wind Tunnel. This model will be used for designing and testing candidate control algorithms before implementation.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217714 , AIAA Paper 2012-4149 , E-18419 , 48th Joint Propulsion Conference and Exhibit; Jul 30, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 77
    Publication Date: 2019-07-13
    Description: The development of techniques for the health monitoring of the rotating components in gas turbine engines is of major interest to NASA s Aviation Safety Program. As part of this on-going effort several experiments utilizing a novel optical Moir based concept along with external blade tip clearance and shaft displacement instrumentation were conducted on a simulated turbine engine disk as a means of demonstrating a potential optical crack detection technique. A Moir pattern results from the overlap of two repetitive patterns with slightly different periods. With this technique, it is possible to detect very small differences in spacing and hence radial growth in a rotating disk due to a flaw such as a crack. The experiment involved etching a circular reference pattern on a subscale engine disk that had a 50.8 mm (2 in.) long notch machined into it to simulate a crack. The disk was operated at speeds up to 12 000 rpm and the Moir pattern due to the shift with respect to the reference pattern was monitored as a means of detecting the radial growth of the disk due to the defect. In addition, blade displacement data were acquired using external blade tip clearance and shaft displacement sensors as a means of confirming the data obtained from the optical technique. The results of the crack detection experiments and its associated analysis are presented in this paper.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217622 , E-18210 , SMART Structures and Materials and Nondestructive Evaluation and Health Monitoring 2012; Mar 11, 2012 - Mar 15, 2012; San Diego, CA; United States
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  • 78
    Publication Date: 2019-07-13
    Description: A sub-model is developed to account for the drag and heat transfer enhancement resulting from deflagration-to-detonation (DDT) inducing obstacles commonly used in pulse detonation engines (PDE). The sub-model is incorporated as a source term in a time-accurate, quasi-onedimensional, CFD-based PDE simulation. The simulation and sub-model are then validated through comparison with a particular experiment in which limited DDT obstacle parameters were varied. The simulation is then used to examine the relative contributions from drag and heat transfer to the reduced thrust which is observed. It is found that heat transfer is far more significant than aerodynamic drag in this particular experiment.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217629 , AIAA Paper 2009-502 , E-18219 , 47th Aerospace Sciences Meeting; Jan 07, 2009 - Jan 11, 2009; Orlando, FL; United States
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  • 79
    Publication Date: 2019-07-13
    Description: Experiments are performed in a 24.4 mm diameter choked circular hot and cold jets issuing from a sharp-edged orifice at a fully expanded jet Mach number of 1.85. The stagnation temperature of the hot and the cold jets are 319 K and 299 K respectively. The results suggest that temperature effects on the screech amplitude and frequency are manifested for the fundamental, with a reduced amplitude and increased frequency for hot jet relative to the cold jet. Temperature effects on the second harmonic are also observed.
    Keywords: Aircraft Propulsion and Power
    Type: KSC-2012-103 , KSC-2012-103R , 23rd International Congress of Theoretical and Applied Mechanics; Aug 19, 2012 - Aug 24, 2012; Beijing; China
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  • 80
    Publication Date: 2019-07-13
    Description: The objective of this research was to compare the performance of an inductance in-line oil debris sensor and magnetic plug oil debris sensor when detecting transmission component health in the same system under the same operating conditions. Both sensors were installed in series in the NASA Glenn Spiral Bevel Gear Fatigue Rig during tests performed on 5 gear sets (pinion/gear) when different levels of damage occurred on the gear teeth. Results of this analysis found both the inductance in-line oil debris sensor and magnetic plug oil debris sensor have benefits and limitations when detecting gearbox component damage.
    Keywords: Aircraft Propulsion and Power
    Type: E-18116 , AHS International 68th Annual Forum and Technology Display; May 01, 2012 - May 03, 2012; Fort Worth, TX; United States
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  • 81
    Publication Date: 2019-07-13
    Description: This paper covers the propulsion system component modeling and controls development of an integrated nonlinear dynamic simulation for an inlet and engine that can be used for an overall vehicle (APSE) model. The focus here is on developing a methodology for the propulsion model integration, which allows for controls design that prevents inlet instabilities and minimizes the thrust oscillation experienced by the vehicle. Limiting thrust oscillations will be critical to avoid exciting vehicle aeroelastic modes. Model development includes both inlet normal shock position control and engine rotor speed control for a potential supersonic commercial transport. A loop shaping control design process is used that has previously been developed for the engine and verified on linear models, while a simpler approach is used for the inlet control design. Verification of the modeling approach is conducted by simulating a two-dimensional bifurcated inlet and a representative J-85 jet engine previously used in a NASA supersonics project. Preliminary results are presented for the current supersonics project concept variable cycle turbofan engine design.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217273 , E-18029 , 47th Joint Propulsion Conference and Exhibit; Jul 31, 2011 - Aug 03, 2011; San Diego, CA; United States
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  • 82
    Publication Date: 2019-07-13
    Description: NASA's Environmentally Responsible Aviation Project and Subsonic Fixed Wing Project are focused on developing concepts and technologies which may enable dramatic reductions to the environmental impact of future generation subsonic aircraft (Refs. 1 and 2). The open rotor concept (also referred to as the Unducted Fan or advanced turboprop) may allow the achievement of this objective by reducing engine emissions and fuel consumption. To evaluate its potential impact, an open rotor cycle modeling capability is needed. This paper presents the initial development of an open rotor cycle model in the Numerical Propulsion System Simulation (NPSS) computer program which can then be used to evaluate the potential benefit of this engine. The development of this open rotor model necessitated addressing two modeling needs within NPSS. First, a method for evaluating the performance of counter-rotating propellers was needed. Therefore, a new counter-rotating propeller NPSS component was created. This component uses propeller performance maps developed from historic counter-rotating propeller experiments to determine the thrust delivered and power required. Second, several methods for modeling a counter-rotating power turbine within NPSS were explored. These techniques used several combinations of turbine components within NPSS to provide the necessary power to the propellers. Ultimately, a single turbine component with a conventional turbine map was selected. Using these modeling enhancements, an open rotor cycle model was developed in NPSS using a multi-design point approach. The multi-design point (MDP) approach improves the engine cycle analysis process by making it easier to properly size the engine to meet a variety of thrust targets throughout the flight envelope. A number of design points are considered including an aerodynamic design point, sea-level static, takeoff and top of climb. The development of this MDP model was also enabled by the selection of a simple power management scheme which schedules propeller blade angles with the freestream Mach number. Finally, sample open rotor performance results and areas for further model improvements are presented.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2011-217225 , GT2011-46694 , E-17908 , Turbo Expo 2011; Jun 06, 2011 - Jun 10, 2011; Vancouver, BC; Canada
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  • 83
    Publication Date: 2019-07-13
    Description: Combustion noise from turbofan engines has become important, as the noise from sources like the fan and jet are reduced. An aligned and un-aligned coherence technique has been developed to determine a threshold level for the coherence and thereby help to separate the coherent combustion noise source from other noise sources measured with far-field microphones. This method is compared with a statistics based coherence threshold estimation method. In addition, the un-aligned coherence procedure at the same time also reveals periodicities, spectral lines, and undamped sinusoids hidden by broadband turbofan engine noise. In calculating the coherence threshold using a statistical method, one may use either the number of independent records or a larger number corresponding to the number of overlapped records used to create the average. Using data from a turbofan engine and a simulation this paper shows that applying the Fisher z-transform to the un-aligned coherence can aid in making the proper selection of samples and produce a reasonable statistics based coherence threshold. Examples are presented showing that the underlying tonal and coherent broad band structure which is buried under random broadband noise and jet noise can be determined. The method also shows the possible presence of indirect combustion noise. Copyright 2011 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America.
    Keywords: Aircraft Propulsion and Power
    Type: E-17851 , Journal of the Acoustical Society of America (ISSN 0001-4966); 129; 5; 3068-3081
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  • 84
    Publication Date: 2019-07-13
    Description: The paper presents the results from a validation study undertaken as a part of the NASA s fundamental aeronautics initiative on high altitude emissions in order to assess the accuracy of several atomization models used in both non-superheat and superheat spray calculations. As a part of this investigation we have undertaken the validation based on four different cases to investigate the spray characteristics of (1) a flashing jet generated by the sudden release of pressurized R134A from cylindrical nozzle, (2) a liquid jet atomizing in a subsonic cross flow, (3) a Parker-Hannifin pressure swirl atomizer, and (4) a single-element Lean Direct Injector (LDI) combustor experiment. These cases were chosen because of their importance in some aerospace applications. The validation is based on some 3D and axisymmetric calculations involving both reacting and non-reacting sprays. In general, the predicted results provide reasonable agreement for both mean droplet sizes (D32) and average droplet velocities but mostly underestimate the droplets sizes in the inner radial region of a cylindrical jet.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2011-217029 , E-17694 , International Conference on Computational and Experimental Engineering and Sciences (ICCES 2011); Apr 18, 2011 - Apr 21, 2011; Nanjing; China
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  • 85
    Publication Date: 2019-07-13
    Description: Though arc jet testing has been the proven method employed for development testing and certification of TPS and TPS instrumentation, the operational aspects of arc jets limit testing to selected, but constant, conditions. Flight, on the other hand, produces timevarying entry conditions in which the heat flux increases, peaks, and recedes as a vehicle descends through an atmosphere. As a result, we are unable to "test as we fly." Attempts to replicate the time-dependent aerothermal environment of atmospheric entry by varying the arc jet facility operating conditions during a test have proven to be difficult, expensive, and only partially successful. A promising alternative is to rotate the test model exposed to a constant-condition arc jet flow to yield a time-varying test condition at a point on a test article (Fig. 1). The model shape and rotation rate can be engineered so that the heat flux at a point on the model replicates the predicted profile for a particular point on a flight vehicle. This simple concept will enable, for example, calibration of the TPS sensors on the Mars Science Laboratory (MSL) aeroshell for anticipated flight environments.
    Keywords: Aircraft Propulsion and Power
    Type: ARC-E-DAA-TN3214 , 8th International Planetary Probe Workshop (IPPW-8); Jun 06, 2011 - Jun 10, 2011; Portsmouth, VA; United States
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  • 86
    Publication Date: 2019-07-13
    Description: Pressure gain combustion (PGC) has been the object of scientific study for over a century due to its promise of improved thermodynamic efficiency. In many recent application concepts PGC is utilized as a component in an otherwise continuous, normally steady flow system, such as a gas turbine or ram jet engine. However, PGC is inherently unsteady. Failure to account for the effects of this periodic unsteadiness can lead to misunderstanding and errors in performance calculations. This paper seeks to provide some clarity by presenting a consistent method of thermodynamic cycle analysis for a device utilizing PGC technology. The incorporation of the unsteady PGC process into the conservation equations for a continuous flow device is presented. Most importantly, the appropriate method for computing the conservation of momentum is presented. It will be shown that proper, consistent analysis of cyclic conservation principles produces representative performance predictions.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-217831 , AIAA Paper 2013-0280 , E-18582 , 51st Aerospace Science Conference; Jan 07, 2013 - Jan 10, 2013; Grapevine, TX; United States
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  • 87
    Publication Date: 2019-07-13
    Description: This paper presents measurements of temperature and relative species concentrations in the combustion flowfield of a 9-point swirl venturi lean direct injector fueled with JP-8. The temperature and relative species concentrations of the flame produced by the injector were measured using spontaneous Raman scattering (SRS). Results of measurements taken at four flame conditions are presented. The species concentrations reported are measured relative to nitrogen and include oxygen, carbon dioxide, and water.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2013-217830 , AIAA Paper 2013-0562 , E-18581 , 51st Aerospace Sciences Meeting; Jan 07, 2013 - Jan 10, 2013; Grapevine, TX; United States
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  • 88
    Publication Date: 2019-07-13
    Description: Self-tuning aircraft engine models can be applied for control and health management applications. The self-tuning feature of these models minimizes the mismatch between any given engine and the underlying engineering model describing an engine family. This paper provides details of the construction of a self-tuning engine model centered on a piecewise linear Kalman filter design. Starting from a nonlinear transient aerothermal model, a piecewise linear representation is first extracted. The linearization procedure creates a database of trim vectors and state-space matrices that are subsequently scheduled for interpolation based on engine operating point. A series of steady-state Kalman gains can next be constructed from a reduced-order form of the piecewise linear model. Reduction of the piecewise linear model to an observable dimension with respect to available sensed engine measurements can be achieved using either a subset or an optimal linear combination of "health" parameters, which describe engine performance. The resulting piecewise linear Kalman filter is then implemented for faster-than-real-time processing of sensed engine measurements, generating outputs appropriate for trending engine performance, estimating both measured and unmeasured parameters for control purposes, and performing on-board gas-path fault diagnostics. Computational efficiency is achieved by designing multidimensional interpolation algorithms that exploit the shared scheduling of multiple trim vectors and system matrices. An example application illustrates the accuracy of a self-tuning piecewise linear Kalman filter model when applied to a nonlinear turbofan engine simulation. Additional discussions focus on the issue of transient response accuracy and the advantages of a piecewise linear Kalman filter in the context of validation and verification. The techniques described provide a framework for constructing efficient self-tuning aircraft engine models from complex nonlinear simulations.Self-tuning aircraft engine models can be applied for control and health management applications. The self-tuning feature of these models minimizes the mismatch between any given engine and the underlying engineering model describing an engine family. This paper provides details of the construction of a self-tuning engine model centered on a piecewise linear Kalman filter design. Starting from a nonlinear transient aerothermal model, a piecewise linear representation is first extracted. The linearization procedure creates a database of trim vectors and state-space matrices that are subsequently scheduled for interpolation based on engine operating point. A series of steady-state Kalman gains can next be constructed from a reduced-order form of the piecewise linear model. Reduction of the piecewise linear model to an observable dimension with respect to available sensed engine measurements can be achieved using either a subset or an optimal linear combination of "health" parameters, which describe engine performance. The resulting piecewise linear Kalman filter is then implemented for faster-than-real-time processing of sensed engine measurements, generating outputs appropriate for trending engine performance, estimating both measured and unmeasured parameters for control purposes, and performing on-board gas-path fault diagnostics. Computational efficiency is achieved by designing multidimensional interpolation algorithms that exploit the shared scheduling of multiple trim vectors and system matrices. An example application illustrates the accuracy of a self-tuning piecewise linear Kalman filter model when applied to a nonlinear turbofan engine simulation. Additional discussions focus on the issue of transient response accuracy and the advantages of a piecewise linear Kalman filter in the context of validation and verification. The techniques described provide a framework for constructing efficient self-tuning aircraft engine models from complex nonlinear simulatns.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217806 , E-18541 , 2012 Annual Conference Prognostics and Health; Dec 23, 2012 - Dec 27, 2012; Minneapolis, MN; United States
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  • 89
    Publication Date: 2019-07-13
    Description: Current aircraft engine control logic uses a Min-Max control selection structure to prevent the engine from exceeding any safety or operational limits during transients due to throttle commands. This structure is inherently conservative and produces transient responses that are slower than necessary. In order to utilize the existing safety margins more effectively, a modification to this architecture is proposed, referred to as a Conditionally Active (CA) limit regulator. This concept uses the existing Min-Max architecture with the modification that limit regulators are active only when the operating point is close to a particular limit. This paper explores the use of CA limit regulators using a publicly available commercial aircraft engine simulation. The improvement in thrust response while maintaining all necessary safety limits is demonstrated in a number of cases.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217814 , GT2012-70017 , E-18550 , Turbo Expo 2012; Jun 11, 2012 - Jun 15, 2012; COpenhagen; Denmark
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  • 90
    Publication Date: 2019-07-13
    Description: An Ultrasonic Configurable Fan Artificial Noise Source (UCFANS) was designed, built, and tested in support of the Langley Research Center s 14- by 22-Foot wind tunnel test of the Hybrid Wing Body (HWB) full three-dimensional 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of candidate engines using artificial sources (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft and to provide a database for shielding code validation. A range of frequencies, and a parametric study of modes were generated from exhaust and inlet nacelle configurations. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular to the axis of the nacelle (in its 0 orientation) and three planes parallel were acquired from the array sweep. In each plane the linear array traversed five sweeps, for a total span of 160 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Level, and integrated Power Levels are presented in this paper; as well as the in-duct modal structure.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217685 , AIAA Paper-2012-2076 , E-18638 , 2012 Aeroacoustic Conference; Jun 04, 2012 - Jun 06, 2012; Colorado Springs, CO; United States
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  • 91
    Publication Date: 2019-07-13
    Description: This presentation was made at the 2012 Fundamental Aeronautics Program Technical Conference and it covers research work for the Dynamic Modeling of the Variable cycle Propulsion System that was done under the Supersonics Project, in the area of AeroPropulsoServoElasticity. The presentation covers the objective for the propulsion system dynamic modeling work, followed by the work that has been done so far to model the variable Cycle Engine, modeling of the inlet, the nozzle, the modeling that has been done to model the affects of flow distortion, and finally presenting some concluding remarks and future plans.
    Keywords: Aircraft Propulsion and Power
    Type: E-18461 , Fundamental Aeronautics Program Annual Meeting; Mar 13, 2012 - Mar 15, 2012; Cleveland, OH; United States
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  • 92
    Publication Date: 2019-07-13
    Description: The accretion of ice particles in the core of commercial aircraft engines has been an ongoing aviation safety challenge. While no accidents have resulted from this phenomenon to date, numerous engine power loss events ranging from uneventful recoveries to forced landings have been recorded. As a first step to enabling mitigation strategies during ice accretion, a detection scheme must be developed that is capable of being implemented on board modern engines. In this paper, a simple detection scheme is developed and tested using a realistic engine simulation with approximate ice accretion models based on data from a compressor design tool. These accretion models are implemented as modified Low Pressure Compressor maps and have the capability to shift engine performance based on a specified level of ice blockage. Based on results from this model, it is possible to detect the accretion of ice in the engine core by observing shifts in the typical sensed engine outputs. Results are presented in which, for a 0.1 percent false positive rate, a true positive detection rate of 98 percent is achieved.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217742 , AIAA Paper 2012-4649 , E-18487 , Atmospheric Flight Mechanics Conference; Aug 13, 2012 - Aug 16, 2012; Minneapolis, MN; United States
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  • 93
    Publication Date: 2019-07-13
    Description: One of the primary noise sources for Open Rotor systems is the interaction of the forward rotor tip vortex and blade wake with the aft rotor. NASA has collaborated with General Electric on the testing of a new generation of low noise, counterrotating Open Rotor systems. Three-dimensional particle image velocimetry measurements were acquired in the intra-rotor gap of the Historical Baseline blade set. The velocity measurements are of sufficient resolution to characterize the tip vortex size and trajectory as well as the rotor wake decay and turbulence character. The tip clearance vortex trajectory is compared to results from previously developed models. Forward rotor wake velocity profiles are shown. Results are presented in a form as to assist numerical modeling of Open Rotor system aerodynamics and acoustics.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217713 , AIAA Paper 2012-4039 , E-18418 , 48th Joint Propulsion Conference and Exhibit; Jul 30, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 94
    Publication Date: 2019-07-13
    Description: With the increased emphasis on aircraft safety, enhanced performance and affordability, and the need to reduce the environmental impact of aircraft, there are many new challenges being faced by the designers of aircraft propulsion systems. The Controls and Dynamics Branch (CDB) at NASA (National Aeronautics and Space Administration) Glenn Research Center (GRC) in Cleveland, Ohio, is leading and participating in various projects in partnership with other organizations within GRC and across NASA, the U.S. aerospace industry, and academia to develop advanced controls and health management technologies that will help meet these challenges through the concept of an Intelligent Engine. CDB conducts propulsion control and diagnostics research in support of various programs and projects under the NASA Aeronautics Research Mission Directorate and the Human Exploration and Operations Mission Directorate. The paper first provides an overview of the various research tasks in CDB relative to the NASA programs and projects, and briefly describes the progress being made on each of these tasks. The discussion here is at a high level providing the objectives of the tasks, the technical challenges in meeting the objectives and most recent accomplishments. References are provided for each of the technical tasks for the reader to familiarize themselves with the details.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217718 , AIAA Paper 2012-4255 , E-18429 , 48th Joint Propulsion Conference and Exhibit; Jul 30, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 95
    Publication Date: 2019-07-13
    Description: The objective of this paper is to set propulsion system targets for an all-electric manned helicopter of ultra-light utility class to achieve performance comparable to combustion engines. The approach is to begin with a current two-seat helicopter (Robinson R 22 Beta II-like), design an all-electric power plant as replacement for its existing piston engine, and study performance of the new all-electric aircraft. The new power plant consists of high-pressure Proton Exchange Membrane fuel cells, hydrogen stored in 700 bar type-4 tanks, lithium-ion batteries, and an AC synchronous permanent magnet motor. The aircraft and the transmission are assumed to remain the same. The paper surveys the state of the art in each of these areas, synthesizes a power plant using best available technologies in each, examines the performance achievable by such a power plant, identifies key barriers, and sets future technology targets to achieve performance at par with current internal combustion engines.
    Keywords: Aircraft Propulsion and Power
    Type: ARC-E-DAA-TN5817 , 12th AIAA Aviation Technology, Integration, and Operations; Sep 16, 2012; Indianapolis, IN; United States
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  • 96
    Publication Date: 2019-07-13
    Description: An understanding of liquid fuel behavior at superheat conditions is identified to be a topic of importance in the design of modern supersonic engines. As a part of the NASA's supersonics project office initiative on high altitude emissions, we have undertaken an effort to assess the accuracy of various existing CFD models used in the modeling of superheated sprays. As a part of this investigation, we have completed the implementation of a modeling approach into the national combustion code (NCC), and then applied it to investigate the following three cases: (1) the validation of a flashing jet generated by the sudden release of pressurized R134A from a cylindrical nozzle, (2) the differences between two superheat vaporization models were studied based on both hot and cold flow calculations of a Parker-Hannifin pressure swirl atomizer, (3) the spray characteristics generated by a single-element LDI (Lean Direct Injector) experiment were studied to investigate the differences between superheat and non-superheat conditions. Further details can be found in the paper.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217295 , E-18044 , 48th Joint Propulsion Conference and Exhibit; Jul 30, 2012 - Aug 01, 2012; Atlanta, GA; United States
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  • 97
    Publication Date: 2019-07-13
    Description: A methodology is described whereby the work extracted by a turbine exposed to the fundamentally nonuniform flowfield from a representative pressure gain combustor (PGC) may be assessed. The method uses an idealized constant volume cycle, often referred to as an Atkinson or Humphrey cycle, to model the PGC. Output from this model is used as input to a scalable turbine efficiency function (i.e., a map), which in turn allows for the calculation of useful work throughout the cycle. Integration over the entire cycle yields mass-averaged work extraction. The unsteady turbine work extraction is compared to steady work extraction calculations based on various averaging techniques for characterizing the combustor exit pressure and temperature. It is found that averages associated with momentum flux (as opposed to entropy or kinetic energy) provide the best match. This result suggests that momentum-based averaging is the most appropriate figure-of-merit to use as a PGC performance metric. Using the mass-averaged work extraction methodology, it is also found that the design turbine pressure ratio for maximum work extraction is significantly higher than that for a turbine fed by a constant pressure combustor with similar inlet conditions and equivalence ratio. Limited results are presented whereby the constant volume cycle is replaced by output from a detonation-based PGC simulation. The results in terms of averaging techniques and design pressure ratio are similar.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217443 , AIAA Paper 2012-770 , E-18174 , 50th Aerospace Science Conference; Jan 09, 2012 - Jan 12, 2012; Nashville, TN; United States
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  • 98
    Publication Date: 2019-07-13
    Description: An on-board diagnostic architecture for aircraft turbofan engine performance trending, parameter estimation, and gas-path fault detection and isolation has been developed and evaluated in a simulation environment. The architecture incorporates two independent models: a realtime self-tuning performance model providing parameter estimates and a performance baseline model for diagnostic purposes reflecting long-term engine degradation trends. This architecture was evaluated using flight profiles generated from a nonlinear model with realistic fleet engine health degradation distributions and sensor noise. The architecture was found to produce acceptable estimates of engine health and unmeasured parameters, and the integrated diagnostic algorithms were able to perform correct fault isolation in approximately 70 percent of the tested cases
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217279 , AIAA Paper-2011-5859 , E-18034 , 47th Joint Propulsion Conference and Exhibit; Jul 31, 2011 - Aug 03, 2011
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  • 99
    Publication Date: 2019-07-13
    Description: An enhanced design methodology for minimizing the error in on-line Kalman filter-based aircraft engine performance estimation applications is presented in this paper. It specific-ally addresses the under-determined estimation problem, in which there are more unknown parameters than available sensor measurements. This work builds upon an existing technique for systematically selecting a model tuning parameter vector of appropriate dimension to enable estimation by a Kalman filter, while minimizing the estimation error in the parameters of interest. While the existing technique was optimized for open-loop engine operation at a fixed design point, in this paper an alternative formulation is presented that enables the technique to be optimized for an engine operating under closed-loop control throughout the flight envelope. The theoretical Kalman filter mean squared estimation error at a steady-state closed-loop operating point is derived, and the tuner selection approach applied to minimize this error is discussed. A technique for constructing a globally optimal tuning parameter vector, which enables full-envelope application of the technology, is also presented, along with design steps for adjusting the dynamic response of the Kalman filter state estimates. Results from the application of the technique to linear and nonlinear aircraft engine simulations are presented and compared to the conventional approach of tuner selection. The new methodology is shown to yield a significant improvement in on-line Kalman filter estimation accuracy.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217278 , GT2011-46408 , E-18033 , Turbo Expo 2011; Jun 06, 2011 - Jun 10, 2011; Vancouver, BC; Canada
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  • 100
    Publication Date: 2019-07-13
    Description: This paper studies the effect of modifying the control limits of an aircraft engine to obtain additional performance. In an emergency situation, the ability to operate an engine above its normal operating limits and thereby gain additional performance may aid in the recovery of a distressed aircraft. However, the modification of an engine s limits is complex due to the risk of an engine failure. This paper focuses on the tradeoff between enhanced performance and risk of either incurring a mechanical engine failure or compromising engine operability. The ultimate goal is to increase the engine performance, without a large increase in risk of an engine failure, in order to increase the probability of recovering the distressed aircraft. The control limit modifications proposed are to extend the rotor speeds, temperatures, and pressures to allow more thrust to be produced by the engine, or to increase the rotor accelerations and allow the engine to follow a fast transient. These modifications do result in increased performance; however this study indicates that these modifications also lead to an increased risk of engine failure.
    Keywords: Aircraft Propulsion and Power
    Type: NASA/TM-2012-217261 , AIAA Paper 2011-5972 , E-18017 , 47th Joint Propulsion Conference and Exhibit; Jul 31, 2011 - Aug 03, 2011; San Diego, CA; United States
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