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  • 1
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    Significance of shock structure on supersonic jet mixing noise of axisymmetric nozzles (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: One of the key technical elements in NASA's high speed research program is reducing the noise level to meet the federal noise regulation. The dominant noise source is associated with the supersonic jet discharged from the engine exhaust system. Whereas the turbulence mixing is largely responsible for the generation of the jet noise, a broadband shock-associated noise is also generated when the nozzle operates at conditions other than its design. For both mixing and shock noise components, because the source of the noise is embedded in the jet plume, one can expect that jet noise can be predicted from the jet flowfield computation. Mani et al. developed a unified aerodynamic/acoustic prediction scheme by applying an extension of Reichardt's aerodynamic model to compute turbulent shear stresses which are utilized in estimating the strength of the noise source. Although this method produces a fast and practical estimate of the jet noise, a modification by Khavaran et al. has led to an improvement in aerodynamic solution. The most notable feature in this work is that Reichardt's model is replaced with the computational fluid dynamics (CFD) solution of Reynolds-averaged Navier-Stokes equations. The major advantage of this work is that the essential, noise-related flow quantities such as turbulence intensity and shock strength can be better predicted. The predictions were limited to a shock-free design condition and the effect of shock structure on the jet mixing noise was not addressed. The present work is aimed at investigating this issue. Under imperfectly expanded conditions the existence of the shock cell structure and its interaction with the convecting turbulence structure may not only generate a broadband shock-associated noise but also change the turbulence structure, and thus the strength of the mixing noise source. Failure in capturing shock structures properly could lead to incorrect aeroacoustic predictions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 32; 9; p. 1920-1923
    Format: text
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  • 2
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    A survey of the broadband shock associated noise prediction methods (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Several different prediction methods to estimate the broadband shock associated noise of a supersonic jet are introduced and compared with experimental data at various test conditions. The nozzle geometries considered for comparison include a convergent and a convergent-divergent nozzle, both axisymmetric. Capabilities and limitations of prediction methods in incorporating the two nozzle geometries, flight effect, and temperature effect are discussed. Predicted noise field shows the best agreement for a convergent nozzle geometry under static conditions. Predicted results for nozzles in flight show larger discrepancies from data and more dependable flight data are required for further comparison. Qualitative effects of jet temperature, as observed in experiment, are reproduced in predicted results.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 92-0501
    Format: text
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  • 3
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    An Aerodynamic Analysis of a Mixed Flow Turbine (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The aerodynamic performance of a high-work Mixed Flow Turbine (MFT) is computed and compared with experimental data. A three dimensional (3-D) viscous analysis is applied to the single stage MFT geometry with a relatively long upstream transition duct. Predicted vane surface static pressures and circumferentially averaged spanwise quantities at stator and rotor exits agree favorably with data. Compared to the results of axisymmetric flow analysis from design intent, the 3-D computation agrees much better especially in the endwall regions where throughflow prediction fails to assess the loss mechanism properly. Potential sources of performance loss such as tip leakage and secondary flows are also properly captured by the analysis.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-TM-106674 , E-9008 , NAS 1.15:106674 , ARL-TR-572 , Joint Propulsion Conference; Jun 27, 1994 - Jun 29, 1994; Indianapolis, IN; United States
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  • 4
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    Computation of supersonic jet noise under imperfectly expanded conditions (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The turbulent mixing noise of supersonic jet under imperfectly expanded conditions is calculated for convergent and convergent-divergent (CD) axisymmetric nozzle geometries. The noise prediction incorporates CFD solution of Navier-Stokes equations. The effect of grid resolution on shock structure computation is demonstrated. Mixing noise spectra predicted from fine and coarse grid solutions exhibit little sensitivity to the grid resolution. A proper grid resolution, however, results in a significant improvement in shock capturing capability and helps predictions agree favorably with experimental data. Good agreement between predicted noise spectra and data shows that the CFD-incorporated noise prediction scheme, which was demonstrated for shock-free conditions, works as well for shock-containing flow conditions.
    Keywords: ACOUSTICS
    Type: NASA-TM-105961 , E-7481 , NAS 1.15:105961 , AIAA PAPER 93-0735 , Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
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  • 5
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    A survey of the broadband shock associated noise prediction methods (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Several different prediction methods to estimate the broadband shock associated noise of a supersonic jet are introduced and compared with experimental data at various test conditions. The nozzle geometries considered for comparison include a convergent and a convergent-divergent nozzle, both axisymmetric. Capabilities and limitations of prediction methods in incorporating the two nozzle geometries, flight effect, and temperature effect are discussed. Predicted noise field shows the best agreement for a convergent nozzle geometry under static conditions. Predicted results for nozzles in flight show larger discrepancies from data and more dependable flight data are required for further comparison. Qualitative effects of jet temperature, as observed in experiment, are reproduced in predicted results.
    Keywords: ACOUSTICS
    Type: NASA-TM-105365 , E-6743 , NAS 1.15:105365 , AIAA PAPER 92-0501 , Aerospace Sciences Meeting and Exhibit; Jan 06, 1992 - Jan 09, 1992; Reno, NV; United States
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  • 6
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    Computation of supersonic jet mixing noise for an axisymmetric CD nozzle using k-epsilon turbulence model (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The turbulent mixing noise of a supersonic jet is calculated for a round convergent-divergent nozzle at the design pressure ratio. Aerodynamic computations are performed using the PARC code with a k-epsilon turbulence model. Lighthill's acoustic analogy combined with Ribner's assumption is adopted. The acoustics solution is based upon the methodology followed by GE in the MGB code. The source correlation function is expressed as a linear combination of second-order tensors. Assuming separable second-order correlations and incorporating Batchelor's isotropic turbulence model, the source term was calculated from the kinetic energy of turbulence. A Gaussian distribution for the time-delay of correlation was introduced. The computational fluid dynamics (CFD) solution was used to obtain the source strength as well as the characteristic time-delay of correlation. The effect of sound/flow interaction was incorporated using the high frequency asymptotic solution to Lilley's equation for axisymmetric geometries. Acoustic results include sound pressure level directivity and spectra at different polar angles. The aerodynamic and acoustic results demonstrate favorable agreement with experimental data.
    Keywords: ACOUSTICS
    Type: NASA-TM-105338 , E-6705 , NAS 1.15:105338 , AIAA PAPER 92-0500 , Aerospace Sciences Meeting and Exhibit; Jan 06, 1992 - Jan 09, 1992; Reno, NV; United States
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  • 7
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    Computation of supersonic jet noise under imperfectly expanded conditions (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The turbulent mixing noise of supersonic jet under imperfectly expanded conditions is calculated for convergent and convergent-divergent (CD) axisymmetric nozzle geometries. The noise prediction incorporates CFD solution of Navier-Stokes equations. The effect of grid resolution on shock structure computation is demonstrated. Mixing noise spectra predicted from fine and coarse grid solutions exhibit little sensitivity to the grid resolution. A proper grid resolution, however, results in a significant improvement in shock capturing capability and helps predictions agree favorably with experimental data. Good agreement between predicted noise spectra and data shows that the CFD-incorporated noise prediction scheme, which was demonstrated for shock-free conditions, works as well for shock-containing flow conditions.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 93-0735 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 10 p.
    Format: text
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  • 8
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    An Assessment of Gigabit Ethernet Technology and Its Applications at the NASA Glenn Research Center (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: This paper describes Gigabit Ethernet and its role in supporting R&D programs at NASA Glenn. These programs require an advanced high-speed network capable of transporting multimedia traffic, including real-time visualization, high- resolution graphics, and scientific data. GigE is a 1 Gbps extension to 10 and 100 Mbps Ethernet. The IEEE 802.3z and 802.3ab standards define the MAC layer and 1000BASE-X and 1000BASE-T physical layer specifications for GigE. GigE switches and buffered distributors support IEEE 802.3x flow control. The paper also compares GigE with ATM in terms of quality of service, data rate, throughput, scalability, interoperability, network management, and cost of ownership.
    Keywords: Computer Systems
    Type: NASA/TM-2000-209803 , E-12108 , NAS 1.15:209803
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  • 9
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    Modeling and Performance Simulation of the Mass Storage Network Environment (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: This paper describes the application of modeling and simulation in evaluating and predicting the performance of the mass storage network environment. Network traffic is generated to mimic the realistic pattern of file transfer, electronic mail, and web browsing. The behavior and performance of the mass storage network and a typical client-server Local Area Network (LAN) are investigated by modeling and simulation. Performance characteristics in throughput and delay demonstrate the important role of modeling and simulation in network engineering and capacity planning.
    Keywords: Systems Analysis and Operations Research
    Type: NASA/TM-2000-210022 , E-12219 , NAS 1.15:210022
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  • 10
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    Web-Based Distributed Simulation of Aeronautical Propulsion System (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An application was developed to allow users to run and view the Numerical Propulsion System Simulation (NPSS) engine simulations from web browsers. Simulations were performed on multiple INFORMATION POWER GRID (IPG) test beds. The Common Object Request Broker Architecture (CORBA) was used for brokering data exchange among machines and IPG/Globus for job scheduling and remote process invocation. Web server scripting was performed by JavaServer Pages (JSP). This application has proven to be an effective and efficient way to couple heterogeneous distributed components.
    Keywords: Computer Programming and Software
    Type: NASA/TM-2001-210818 , NAS 1.15:210818 , E-12733 , 10th International Symposium on High Performance Distributed Computing; Aug 07, 2001 - Aug 09, 2001; San Francisco, CA; United States
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