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  • 1
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    Effects of curvature and rotation on turbulence in the NASA low-speed centrifugal compressor impeller (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The flow in the NASA Low-Speed Impeller is affected by both curvature and rotation. The flow curves due to the following: (1) geometric curvature, e.g. the curvature of the hub and shroud profiles in the meridional plane and the curvature of the backswept impeller blades; and (2) secondary flow vortices, e.g. the tip leakage vortex. Changes in the turbulence and effective turbulent viscosity in the impeller are investigated. The effects of these changes on three-dimensional flow development are discussed. Two predictions of the flow in the impeller, one with, and one without modification to the turbulent viscosity due to rotation and curvature, are compared. Some experimental and theoretical background for the modified mixing length model of turbulent viscosity will also be presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Goddard Space Flight Center, Tenth Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion, Part 1; p 315-338
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  • 2
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    Explicit finite-volume time-marching calculations of total temperature distributions in turbulent flow (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A method was developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time-marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier-Stokes equations. The entire calculation is performed in the physical domain. This paper investigates the introduction of a new formulation of the energy equation which gives improved transient behavior as the calculation converges. The effect of variable Prandtl number on the temperature distribution through the boundary layer is also investigated. A turbulent boundary layer in an adverse pressure gradient (M = 0.55) is used to demonstrate the improved transient temperature distribution obtained when the new formulation of the energy equation is used. A flat plate turbulent boundary layer with a supersonic free-stream Mach number of 2.8 is used to investigate the effect of Prandtl number on the distribution of properties through the boundary layer. The computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Thermodynamic Evaluation of Transonic Compressor Rotors Using the Finite Volume Approach; p 71-82
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  • 3
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    An explicit finite-volume time-marching procedure for turbulent flow calculations (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A method was developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite-volume, time-marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier-Stokes equations. The entire calculation is performed in the physical domain. Control volumes are chosen so that smoothing of flow properties, typically required for stability, is not required. Different time steps are used in the different governing equations. A new pressure interpolation scheme is introduced which improves the shock capturing ability of the method. A multi-volume method for pressure changes in the boundary layer allows calculations which use very long and thin control volumes (length/height - 1000). The method is compared with two test cases. Essentially incompressible turbulent boundary layer flow in an adverse pressure gradient is calculated and the computed distributions of mean velocity and shear are in good agreement with the measurements. Transonic viscous flow in a converging diverging nozzle is calculated; the Mach number upstream of the shock is approximately 1.25. The agreement between the calculated and measured shock strength and total pressure losses is good.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Thermodynamic Evaluation of Transonic Compressor Rotors Using the Finite Volume Approach; p 59-70
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  • 4
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    A prediction of 3-D viscous flow and performance of the NASA Low-Speed Centrifugal Compressor (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A prediction of the three-dimensional turbulent flow in the NASA Low-Speed Centrifugal Compressor Impeller has been made. The calculation was made for the compressor design conditions with the specified uniform tip clearance gap. The predicted performance is significantly worse than that predicted in the NASA design study. This is explained by the high tip leakage flow in the present calculation and by the different model adopted for tip leakage flow mixing. The calculation gives an accumulation of high losses in the shroud/pressure-side quadrant near the exit of the impeller. It also predicts a region of meridional backflow near the shroud wall. Both of these flow features should be extensive enough in the NASA impeller to allow detailed flow measurements, leading to improved flow modeling. Recommendations are made for future flow studies in the NASA impeller.
    Keywords: AERODYNAMICS
    Type: ASME PAPER 90-GT-234
    Format: text
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  • 5
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    External stress-corrosion cracking of a 1.22-m-diameter type 316 stainless steel air valve (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An investigation was conducted to determine the cause of the failure of a massive AISI Type 316 stainless steel valve which controlled combustion air to a jet engine test facility. Several through-the-wall cracks were present near welded joints in the valve skirt. The valve had been in outdoor service for 18 years. Samples were taken in the cracked regions for metallographic and chemical analyses. Insulating material and sources of water mist in the vicinity of the failed valve were analyzed for chlorides. A scanning electron microscope was used to determine whether foreign elements were present in a crack. On the basis of the information generated, the failure was characterized as external stress-corrosion cracking. The cracking resulted from a combination of residual tensile stress from welding and the presence of aqueous chlorides. Recommended countermeasures are included.
    Keywords: METALLIC MATERIALS
    Type: NASA-TP-3190 , E-6810 , NAS 1.60:3190
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  • 6
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    A prediction of 3-D viscous flow and performance of the NASA low-speed centrifugal compressor (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A prediction of the 3-D turbulent flow in the NASA Low-Speed Centrifugal Compressor Impeller has been made. The calculation was made for the compressor design conditions with the specified uniform tip clearance gap. The predicted performance is significantly worse than that predicted in the NASA design study. This is explained by the high tip leakage flow in the present calculation and by the different model adopted for tip leakage flow mixing. The calculation gives an accumulation for high losses in the shroud/pressure-side quadrant near the exit of the impeller. It also predicts a region of meridional backflow near the shroud wall. Both of these flow features should be extensive enough in the NASA impeller to allow detailed flow measurements, leading to improved flow modelling. Recommendations are made for future flow studies in the NASA impeller.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-184765 , NAS 1.26:184765 , TRG-JM/89-1
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  • 7
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    ASTP experiment support data processing (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Activities associated with the generation of ASTP experiment support data in the areas of spacecraft ephemeris and orientation and instrument pointing and field-of-view are documented. It is intended that this document represent a cradle-to-grave chronicle of these activities. To satisfy this intent while facilitating the ready dissemination of information, the document is being published twice. The first publication, scheduled for release prior to ASTP liftoff, includes all preflight phases of the experiment support activity in addition to those appendixes that do not pertain to any mission-specific data. The second publication will provide any required updates to the original documentation and will add all mission-specific data, including documentation of all postflight data processing activities and data archiving information.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-141915 , JSC-09794 , JSC-IN-75-FM-49
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  • 8
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    Low Order Wavefront Sensing and Control for WFIRST Coronagraph (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-20
    Description: To maintain the required WFIRST Coronagraph starlight suppression performance in a realistic space environment, a low order wavefront sensing and control (LOWFS/C) subsystem is necessary. The LOWFS/C uses the rejected stellar light from coronagraph to sense and suppress the telescope pointing drift and jitter as well as the low order wavefront errors due to changes in thermal loading on the telescope and the rest of the observatory. In this paper we will present an overview of the low order wavefront sensing and control subsystem for the WFIRST Coronagraph and describe the WFIRST Coronagraph LOWFS function, its design, and modeled performance. We will present experimental results on a dedicated LOWFS/C testbed that show that the LOWFS/C subsystem not only can sense pointing errors better than 0.2 mas but has also experimentally demonstrated closed loop pointing error suppression with residuals better than 0.4 mas rms per axis for the vast majority of observatory reaction wheel speeds.
    Keywords: Astrophysics; Instrumentation and Photography
    Type: JPL-CL-16-3033 , SPIE Astronomical Telescopes + Instrumentation 2016; Jun 26, 2016 - Jul 01, 2016; Edinburgh, Scotland; United Kingdom
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  • 9
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    Infrared Spectra and Optical Constants of Nitrile Ices Relevant to Titan's Atmosphere (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: Spectra and optical constants of nitrile ices known or suspected to be in Titan?s atmosphere have been determined from 2.0 to 333.3 microns (approx.5000 to 30/cm). These results are relevant to the ongoing modeling of Cassini CIRS observations of Titan?s winter pole. Ices studied were: HCN, hydrogen cyanide; C2N2, cyanogen; CH3CN, acetonitrile; C2H5CN, propionitrile; and HC3N, cyanoacetylene. Optical constants were calculated, using Kramers-Kronig analysis, for each nitrile ice?s spectrum measured at a variety of temperatures, in both the amorphous- and crystalline phases. Spectra were also measured for many of the nitriles after quenching at the annealing temperature and compared with those of annealed ices. For each of these molecules we also measured the real component, n, of the refractive index for amorphous and crystalline phases at 670 nm. Several examples of the information contained in these new data sets and their usefulness in modeling Titan?s observed features will be presented (e.g., the broad emission feature at 160/cm; Anderson and Samuelson, 2011).
    Keywords: Chemistry and Materials (General)
    Type: Titan Chemistry -- Observations, Experiments, Computations, and Modeling; Apr 11, 2011 - Apr 14, 2011; Kauai, HI; United States
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  • 10
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    Observational Needs for Improving Ocean and Coupled Reanalysis, S2S Prediction, and Decadal Prediction (2019)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Developments in ocean data assimilation (DA) and observing system technologies are intertwined. New observation types lead to new DA methods, and new DA methods such as Coupled Data Assimilation can change the value of existing observations or indicate where new observations can have greater utility for monitoring and prediction. Practitioners are encouraged to make better use of observations that are already available, for example in strongly coupled data assimilation where ocean observations can be used to improve atmospheric analyses and vice versa. Ocean reanalyses are useful for the analysis of climate,as well as initializing operational long-range prediction models. There are remaining challenges for ocean reanalyses due to biases and abrupt changes in the ocean observing system throughout its history, the presence of biases and drifts in models, and simplifying assumptions made in the DA methods. From a governance point of view, more support is needed to interface the observing community and the ocean DA community. For prediction applications, the ocean DA community must work with the ocean observing community to establish protocols for rapid communication of ocean observing data on NWP timescales. There is potential for new observations to enhance the observing system by supporting prediction on multiple timescales, ranging from the typical timescale of numerical weather prediction covering hours to weeks, out to multiple decades. It is highly encouraged that communication be fostered between thesecommunities to allow operational prediction centers the ability to provide guidance to the design of a sustained and adaptive observing network.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN70691 , Frontiers in Marine Science (e-ISSN 2296-7745); 6; 391
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