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  • 1
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    Preconditioned Conjugate Gradient Methods for the Navier-Stokes Equations (1994)
    Elsevier
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0021-9991
    Electronic ISSN: 1090-2716
    Topics: Computer Science , Physics
    Published by Elsevier
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    PAPER CURRENT
  • 2
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    Preconditioned conjugate gradient methods for the Navier-Stokes equations (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A preconditioned Krylov subspace method (GMRES) is used to solve the linear systems of equations formed at each time-integration step of the unsteady, two-dimensional, compressible Navier-Stokes equations of fluid flow. The Navier-Stokes equations are cast in an implicit, upwind finite-volume, flux-split formulation. Several preconditioning techniques are investigated to enhance the efficiency and convergence rate of the implicit solver based on the GMRES algorithm. The superiority of the new solver is established by comparisons with a conventional implicit solver, namely line Gauss-Seidel relaxation (LGSR). Computational test results for low-speed (incompressible flow over a backward-facing step at Mach 0.1), transonic flow (trailing edge flow in a transonic turbine cascade), and hypersonic flow (shock-on-shock interactions on a cylindrical leading edge at Mach 6.0) are presented. For the Mach 0.1 case, overall speedup factors of up to 17 (in terms of time-steps) and 15 (in terms of CPU time on a CRAY-YMP/8) are found in favor of the preconditioned GMRES solver, when compared with the LGSR solver. The corresponding speedup factors for the transonic flow case are 17 and 23, respectively. The hypersonic flow case shows slightly lower speedup factors of 9 and 13, respectively. The study of preconditioners conducted in this research reveals that a new LUSGS-type preconditioner is much more efficient than a conventional incomplete LU-type preconditioner.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 110; 1; p. 68-81
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Discrete sensitivity derivatives of the Navier-Stokes equations with a parallel Krylov solver (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper solves an 'incremental' form of the sensitivity equations derived by differentiating the discretized thin-layer Navier Stokes equations with respect to certain design variables of interest. The equations are solved with a parallel, preconditioned Generalized Minimal RESidual (GMRES) solver on a distributed-memory architecture. The 'serial' sensitivity analysis code is parallelized by using the Single Program Multiple Data (SPMD) programming model, domain decomposition techniques, and message-passing tools. Sensitivity derivatives are computed for low and high Reynolds number flows over a NACA 1406 airfoil on a 32-processor Intel Hypercube, and found to be identical to those computed on a single-processor Cray Y-MP. It is estimated that the parallel sensitivity analysis code has to be run on 40-50 processors of the Intel Hypercube in order to match the single-processor processing time of a Cray Y-MP.
    Keywords: PROPELLANTS AND FUELS
    Type: NASA-TM-106481 , ICOMP-94-2 , E-8411 , NAS 1.15:106481 , AIAA PAPER 94-0091 , Aerospace Sciences Meeting and Exhibit; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
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    NASA TECHNICAL REPORTS
  • 4
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    Preconditioned implicit solvers for the Navier-Stokes equations on distributed-memory machines (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The GMRES method is parallelized, and combined with local preconditioning to construct an implicit parallel solver to obtain steady-state solutions for the Navier-Stokes equations of fluid flow on distributed-memory machines. The new implicit parallel solver is designed to preserve the convergence rate of the equivalent 'serial' solver. A static domain-decomposition is used to partition the computational domain amongst the available processing nodes of the parallel machine. The SPMD (Single-Program Multiple-Data) programming model is combined with message-passing tools to develop the parallel code on a 32-node Intel Hypercube and a 512-node Intel Delta machine. The implicit parallel solver is validated for internal and external flow problems, and is found to compare identically with flow solutions obtained on a Cray Y-MP/8. A peak computational speed of 2300 MFlops/sec has been achieved on 512 nodes of the Intel Delta machine,k for a problem size of 1024 K equations (256 K grid points).
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-TM-106449 , E-8302 , ICOMP-93-49 , NAS 1.15:106449 , AIAA PAPER 94-0408 , Aerospace Sciences Meeting and Exhibit; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
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    NASA TECHNICAL REPORTS
  • 5
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    Assessment of Reduced-Kinetics Mechanisms for Combustion of Jet Fuel in CFD Applications (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A computational effort was undertaken to analyze the details of fluid flow in Lean-Direct Injection (LDI) combustors for next-generation LDI design. The National Combustor Code (NCC) was used to perform reacting flow computations on single-element LDI injector configurations. The feasibility of using a reduced chemical-kinetics approach, which optimizes the reaction rates and species to model the emissions characteristics typical of lean-burning gas-turbine combustors, was assessed. The assessments were performed with Reynolds- Averaged Navier-Stokes (RANS) and Time-Filtered Navier Stokes (TFNS) time-integration, with a Lagrangian spray model with the NCC code. The NCC predictions for EINOx and combustor exit temperature were compared with experimental data for two different single-element LDI injector configurations, with 60deg and 45deg axially swept swirler vanes. The effects of turbulence-chemistry interaction on the predicted flow in a typical LDI combustor were studied with detailed comparisons of NCC TFNS with experimental data.
    Keywords: Propellants and Fuels; Fluid Mechanics and Thermodynamics
    Type: E-662714 , AIAA Propulsion and Energy 2014 Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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    NASA TECHNICAL REPORTS
  • 6
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    Simulations of NOx Emissions from Low Emissions Discrete Jet Injector Combustor Tests (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An experimental and computational study was conducted to evaluate the performance and emissions characteristics of a candidate Lean Direct Injection (LDI) combustor configuration with a mix of simplex and airblast injectors. The National Combustion Code (NCC) was used to predict the experimentally measured EINOx emissions for test conditions representing low power, medium power, and high-power engine cycle conditions. Of the six cases modeled with the NCC using a reduced-kinetics finite-rate mechanism and lagrangian spray modeling, reasonable predictions of combustor exit temperature and EINOx were obtained at two high-power cycle conditions.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Propulsion and Energy Forum 2014; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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    NASA TECHNICAL REPORTS
  • 7
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    CFD Analysis of Emissions for a Candidate N+3 Combustor (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An effort was undertaken to analyze the performance of a model Lean-Direct Injection (LDI) combustor designed to meet emissions and performance goals for NASA's N+3 program. Computational predictions of Emissions Index (EINOx) and combustor exit temperature were obtained for operation at typical power conditions expected of a small-core, high pressure-ratio (greater than 50), high T3 inlet temperature (greater than 950K) N+3 combustor. Reacting-flow computations were performed with the National Combustion Code (NCC) for a model N+3 LDI combustor, which consisted of a nine-element LDI flame-tube derived from a previous generation (N+2) thirteen-element LDI design. A consistent approach to mesh-optimization, spray-modeling and kinetics-modeling was used, in order to leverage the lessons learned from previous N+2 flame-tube analysis with the NCC. The NCC predictions for the current, non-optimized N+3 combustor operating indicated a 74% increase in NOx emissions as compared to that of the emissions-optimized, parent N+2 LDI combustor.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: ISABE Paper 2015-20245 , GRC-E-DAA-TN27636 , International Symposium on Airbreathing Engines (ISABE 2015); Oct 25, 2015 - Oct 29, 2015; Phoenix, AZ; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    A CFD Analysis of Hydrogen Leakage During On-Pad Purge in the ORION/ARES I Shared Volume (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A common open volume is created by the stacking of the Orion vehicle onto the Ares I Upper Stage. Called the Shared Volume, both vehicles contribute to its gas, fluid, and thermal environment. One of these environments is related to hazardous hydrogen gas. While both vehicles use inert purge gas to mitigate any hazardous gas buildup, there are concerns that hydrogen gas may still accumulate and that the Ares I Hazardous Gas Detection System will not be sufficient for monitoring the integrated volume. This Computational Fluid Dynamics (CFD) analysis has been performed to examine these topics. Results of the analysis conclude that the Ares I Hazardous Gas Detection System will be able to sample the vent effluent containing the highest hydrogen concentrations. A second conclusion is that hydrogen does not accumulate under the Orion Service Module (SM) avionics ring as diffusion and purge flow mixing sufficiently dilute the hydrogen to safe concentrations. Finally the hydrogen concentrations within the Orion SM engine nozzle may slightly exceed the 1 percent volume fraction when the entire worse case maximum full leak is directed vertically into the engine nozzle.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2011-217020 , E-17685
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    NASA TECHNICAL REPORTS
  • 9
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    CFD Analysis of Emissions for a Candidate N+3 Combustor (2015)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: An effort was undertaken to analyze the performance of a model Lean-Direct Injection (LDI) combustor designed to meet emissions and performance goals for NASA's N+3 program. Computational predictions of Emissions Index (EINOx) and combustor exit temperature were obtained for operation at typical power conditions expected of a small-core, high pressure-ratio (greater than 50), high T3 inlet temperature (greater than 950K) N+3 combustor. Reacting-flow computations were performed with the National Combustion Code (NCC) for a model N+3 LDI combustor, which consisted of a nine-element LDI flame-tube derived from a previous generation (N+2) thirteen-element LDI design. A consistent approach to mesh-optimization, spraymodeling and kinetics-modeling was used, in order to leverage the lessons learned from previous N+2 flame-tube analysis with the NCC. The NCC predictions for the current, non-optimized N+3 combustor operating indicated a 74% increase in NOx emissions as compared to that of the emissions-optimized, parent N+2 LDI combustor.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: ISABE-2015-20245 , GRC-E-DAA-TN24255 , International Symposium on Airbreathing Engines (ISABE); Oct 25, 2015 - Oct 30, 2015; Phoenix, AZ; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    LOX/Methane Main Engine Glow Plug Igniter Tests and Modeling (2009)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Ignition data for tests with a LOX/methane igniter that utilized a glow plug as the ignition source are presented. The tests were conducted in a vacuum can with thermally conditioned (cold) hardware. Data showing the effects of glow plug geometry, type, and igniter operating conditions are discussed. Comparisons between experimental results and multidimensional, transient computer models are also made.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2009-215522 , E-16799 , Sixth Modeling and Simulation Subcommittee Meeting; Dec 08, 2008 - Dec 12, 2008; Orlando, FL; United States|Third Spacecraft Propulsion Subcommittee Meeting; Dec 08, 2008 - Dec 12, 2008; Orlando, FL; United States|Fourth Liquid Propulsion Subcommittee Meeting; Dec 08, 2008 - Dec 12, 2008; Orlando, FL; United States
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    NASA TECHNICAL REPORTS
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