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  • 1
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    WRLES: Wave Resolving Large-Eddy Simulation Code, Theory and Usage (2019)
    In:  CASI
    Details
    Publication Date: 2019-05-11
    Description: A computational fluid dynamics code has been developed for large-eddy simulations (LES) of turbulent flow. The code uses high-order of accuracy and high-resolution numerical methods to minimize solution error and maximize the resolution of the turbulent structures. Spatial discretization is performed using explicit central differencing. The central differencing schemes in the code include 2nd- to 12th-order standard central difference methods as well as 7-, 9-, 11- and 13-point dispersion relation preserving schemes. Solution filtering and high-order shock capturing are included for stability. Time discretization is performed using multistage Runge-Kutta methods that are up to 4th order accurate. Several options are available to model turbulence including: Baldwin-Lomax and Spalart-Allmaras Reynolds-averaged Navier-Stokes turbulence models, and Smagorinsky, Dynamic Smagorinsky and Vreman sub-grid scale models for LES. This report presents the theory behind the numerical and physical models used in the code and provides a user's manual to the operation of the code.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2019-220192 , GRC-E-DAA-TN67540
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  • 2
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    NPARC Alliance (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The NPARC Alliance is a cooperative effort between the United States Air Force's Arnold Engineering Development Center, NASA's Glenn Research Center and The Boeing Company. The mission of the Alliance is to develop, validate, and support an integrated, general purpose computational flow simulator for the U.S. aerospace community. The Alliance provides a state of the art simulation system that includes geometry manipulation, flow solution, and post-processing capabilities. The system is centered around the WIND flow solver. This presentation provides an overview of the Alliance and the flowfield simulation system. Several example computations are provided.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA Glenn Research Center UEET (Ultra-Efficient Engine Technology) Program: Agenda and Abstracts; 22
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  • 3
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    Solutions of the Taylor-Green Vortex Problem Using High-Resolution Explicit Finite Difference Methods (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A computational fluid dynamics code that solves the compressible Navier-Stokes equations was applied to the Taylor-Green vortex problem to examine the code s ability to accurately simulate the vortex decay and subsequent turbulence. The code, WRLES (Wave Resolving Large-Eddy Simulation), uses explicit central-differencing to compute the spatial derivatives and explicit Low Dispersion Runge-Kutta methods for the temporal discretization. The flow was first studied and characterized using Bogey & Bailley s 13-point dispersion relation preserving (DRP) scheme. The kinetic energy dissipation rate, computed both directly and from the enstrophy field, vorticity contours, and the energy spectra are examined. Results are in excellent agreement with a reference solution obtained using a spectral method and provide insight into computations of turbulent flows. In addition the following studies were performed: a comparison of 4th-, 8th-, 12th- and DRP spatial differencing schemes, the effect of the solution filtering on the results, the effect of large-eddy simulation sub-grid scale models, and the effect of high-order discretization of the viscous terms.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2013-217850 , E-18637 , 51st Aerospace Sciences Meeting; Jan 07, 2013 - Jan 10, 2013; Grapevine, TX; United States
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  • 4
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    Prediction of Turbulent Temperature Fluctuations in Hot Jets (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Large-eddy simulations were used to investigate turbulent temperature fluctuations and turbulent heat flux in hot jets. A high-resolution finite-difference Navier-Stokes solver, WRLES, was used to compute the flow from a 2-inch round nozzle. Several different flow conditions, consisting of different jet Mach numbers and temperature ratios, were examined. Predictions of mean and fluctuating velocities were compared to previously obtained particle image velocimetry data. Predictions of mean and fluctuating temperature were compared to new data obtained using Raman spectroscopy. Based on the good agreement with experimental data for the individual quantities, the combined quantity turbulent heat flux was examined.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: GRC-E-DAA-TN43225 , AIAA Aviation; Jun 05, 2017 - Jun 09, 2017; Denver, CO; United States
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  • 5
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    The Numerical Analysis of a Turbulent Compressible Jet (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A numerical method to simulate high Reynolds number jet flows was formulated and applied to gain a better understanding of the flow physics. Large-eddy simulation was chosen as the most promising approach to model the turbulent structures due to its compromise between accuracy and computational expense. The filtered Navier-Stokes equations were developed including a total energy form of the energy equation. Subgrid scale models for the momentum and energy equations were adapted from compressible forms of Smagorinsky's original model. The effect of using disparate temporal and spatial accuracy in a numerical scheme was discovered through one-dimensional model problems and a new uniformly fourth-order accurate numerical method was developed. Results from two- and three-dimensional validation exercises show that the code accurately reproduces both viscous and inviscid flows. Numerous axisymmetric jet simulations were performed to investigate the effect of grid resolution, numerical scheme, exit boundary conditions and subgrid scale modeling on the solution and the results were used to guide the three-dimensional calculations. Three-dimensional calculations of a Mach 1.4 jet showed that this LES simulation accurately captures the physics of the turbulent flow. The agreement with experimental data was relatively good and is much better than results in the current literature. Turbulent intensities indicate that the turbulent structures at this level of modeling are not isotropic and this information could lend itself to the development of improved subgrid scale models for LES and turbulence models for RANS simulations. A two point correlation technique was used to quantify the turbulent structures. Two point space correlations were used to obtain a measure of the integral length scale, which proved to be approximately 1/2 D(sub j). Two point space-time correlations were used to obtain the convection velocity for the turbulent structures. This velocity ranged from 0.57 to 0.71 U(sub j).
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2001-210716 , E-12669 , NAS 1.15:210716
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  • 6
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    Comparison of High-Order and Low-Order Methods for Large-Eddy Simulation of a Compressible Shear Layer (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The objective of this work is to compare a high-order solver with a low-order solver for performing Large-Eddy Simulations (LES) of a compressible mixing layer. The high-order method is the Wave-Resolving LES (WRLES) solver employing a Dispersion Relation Preserving (DRP) scheme. The low-order solver is the Wind-US code, which employs the second-order Roe Physical scheme. Both solvers are used to perform LES of the turbulent mixing between two supersonic streams at a convective Mach number of 0.46. The high-order and low-order methods are evaluated at two different levels of grid resolution. For a fine grid resolution, the low-order method produces a very similar solution to the highorder method. At this fine resolution the effects of numerical scheme, subgrid scale modeling, and filtering were found to be negligible. Both methods predict turbulent stresses that are in reasonable agreement with experimental data. However, when the grid resolution is coarsened, the difference between the two solvers becomes apparent. The low-order method deviates from experimental results when the resolution is no longer adequate. The high-order DRP solution shows minimal grid dependence. The effects of subgrid scale modeling and spatial filtering were found to be negligible at both resolutions. For the high-order solver on the fine mesh, a parametric study of the spanwise width was conducted to determine its effect on solution accuracy. An insufficient spanwise width was found to impose an artificial spanwise mode and limit the resolved spanwise modes. We estimate that the spanwise depth needs to be 2.5 times larger than the largest coherent structures to capture the largest spanwise mode and accurately predict turbulent mixing.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2015-218741 , E-19074 , GRC-E-DAA-TN20935 , AIAA Aviation Technology, Integration, and Operations Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 7
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    Evaluation of Inflow Turbulence Methods in Large-Eddy Simulations of a Supersonic Boundary Layer (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: In the context of Large- Eddy Simulations (LES), Boundary-layer inflow turbulence is simulated using both the Synthetic Eddy Model (SEM) and Digital Filtering (DF). The effects of the projection error are investigated. The effect of the prescribed length scales on the adjustment region was found to be negligible for length scales less than one-tenth of the boundary-layer thickness. While it was conjectured that one method of the two might be more robust than the other, our results show that both the Digital Filtering Method and the Synthetic Eddy Method accurately replicate the boundary layer while successfully accounting for inflow turbulence.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: GRC-E-DAA-TN59196 , E-19576 , NASA/TM-2018- 219966
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  • 8
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    Prediction of Turbulent Temperature Fluctuations in Hot Jets (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Large-eddy simulations were used to investigate turbulent temperature fluctuations and turbulent heat flux in hot jets. A high-resolution finite-difference Navier-Stokes solver, WRLES, was used to compute the flow from a 2-inch round nozzle. Several different flow conditions, consisting of different jet Mach numbers and temperature ratios, were examined. Predictions of mean and fluctuating velocities were compared to previously obtained particle image velocimetry data. Predictions of mean and fluctuating temperature were compared to new data obtained using Raman spectroscopy. Based on the good agreement with experimental data for the individual quantities, the combined quantity turbulent heat flux was examined.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2017-219531 , E-19388 , AIAA Paper 2017-3610 , GRC-E-DAA-TN44180
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  • 9
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    A High-Resolution Capability for Large-Eddy Simulation of Jet Flows (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A large-eddy simulation (LES) code that utilizes high-resolution numerical schemes is described and applied to a compressible jet flow. The code is written in a general manner such that the accuracy/resolution of the simulation can be selected by the user. Time discretization is performed using a family of low-dispersion Runge-Kutta schemes, selectable from first- to fourth-order. Spatial discretization is performed using central differencing schemes. Both standard schemes, second- to twelfth-order (3 to 13 point stencils) and Dispersion Relation Preserving schemes from 7 to 13 point stencils are available. The code is written in Fortran 90 and uses hybrid MPI/OpenMP parallelization. The code is applied to the simulation of a Mach 0.9 jet flow. Four-stage third-order Runge-Kutta time stepping and the 13 point DRP spatial discretization scheme of Bogey and Bailly are used. The high resolution numerics used allows for the use of relatively sparse grids. Three levels of grid resolution are examined, 3.5, 6.5, and 9.2 million points. Mean flow, first-order turbulent statistics and turbulent spectra are reported. Good agreement with experimental data for mean flow and first-order turbulent statistics is shown.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2011-216833 , AIAA Paper 2010-5023 , E-17463 , 40th Fluid Dynamics Conference and Exhibit; Jun 28, 2010 - Jul 01, 2010; Chicago, IL; United States
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  • 10
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    Prediction of Turbulent Temperature Fluctuations in Hot Jets (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Large-eddy simulations (LES) were used to investigate turbulent temperature fluctuations and turbulent heat flux in hot jets. A high-resolution finite-difference Navier-Stokes solver was used to compute the flow from a 2-inch round nozzle. Three different flow conditions of varying jet Mach numbers and temperature ratios were examined. The LES results showed that the temperature field behaves similar to the velocity field, but with a more rapidly spreading mixing layer. Predictions of mean, mu-bar(sub i), and fluctuating, mu'(sub i), velocities were compared to particle image velocimetry data. Predictions of mean, T-bar, and fluctuating, T', temperature were compared to data obtained using Rayleigh scattering and Raman spectroscopy. Very good agreement with experimental data was demonstrated for the mean and fluctuating velocities. The LES correctly predicts the behavior of the turbulent temperature field, but over-predicts the levels of the fluctuations. The turbulent heat flux was examined and compared to Reynolds-averaged Navier-Stokes (RANS) results. The LES and RANS simulations produced very similar results for the radial heat flux. However, the axial heat flux obtained from the LES differed significantly from the RANS result in both structure and magnitude, indicating that the gradient diffusion type model in RANS is inadequate. Finally, the LES data was used to compute the turbulent Prandtl number and verify that a constant value of 0.7 used in the RANS models is a reasonable assumption.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: GRC-E-DAA-TN42369 , AIAA Aviation; Jun 05, 2017 - Jun 09, 2017; Denver, CO; United States
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