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Thomas B Gatski - One of the best experts on this subject based on the ideXlab platform.
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direct numerical simulation and analysis of a spatially evolving supersonic turbulent boundary layer at m 2 25
Physics of Fluids, 2004Co-Authors: Sergio Pirozzoli, Francesco Grasso, Thomas B GatskiAbstract:A spatially developing supersonic adiabatic flat plate boundary layer flow (at M∞=2.25 and Reθ≈4000) is analyzed by means of direct numerical simulation. The numerical algorithm is based on a mixed weighted essentially nonoscillatory compact-difference method for the three-dimensional Navier–Stokes equations. The main objectives are to assess the validity of Morkovin’s hypothesis and Reynolds analogies, and to analyze the controlling mechanisms for turbulence production, dissipation, and transport. The results show that the essential dynamics of the investigated turbulent supersonic boundary layer flow closely resembles the incompressible pattern. The Van Driest transformed mean velocity obeys the incompressible law-of-the-wall, and the mean Static Temperature field exhibits a quadratic dependency upon the mean velocity, as predicted by the Crocco–Busemann relation. The total Temperature has been found not to be precisely uniform, and total Temperature fluctuations are found to be non-negligible. Consistently, the turbulent Prandtl number is not unity, and it varies between 0.7 and 0.8 in the outer part of the boundary layer. Nonetheless, a modified strong Reynolds analogy is still verified. In agreement with the low Mach number results, the streamwise velocity component and the Temperature are only weakly anti-correlated. The turbulent kinetic energy budget also shows similarities with the incompressible case provided all terms of the equation are properly scaled; indeed, the leading compressibility contributions are negligible throughout the boundary layer.A spatially developing supersonic adiabatic flat plate boundary layer flow (at M∞=2.25 and Reθ≈4000) is analyzed by means of direct numerical simulation. The numerical algorithm is based on a mixed weighted essentially nonoscillatory compact-difference method for the three-dimensional Navier–Stokes equations. The main objectives are to assess the validity of Morkovin’s hypothesis and Reynolds analogies, and to analyze the controlling mechanisms for turbulence production, dissipation, and transport. The results show that the essential dynamics of the investigated turbulent supersonic boundary layer flow closely resembles the incompressible pattern. The Van Driest transformed mean velocity obeys the incompressible law-of-the-wall, and the mean Static Temperature field exhibits a quadratic dependency upon the mean velocity, as predicted by the Crocco–Busemann relation. The total Temperature has been found not to be precisely uniform, and total Temperature fluctuations are found to be non-negligible. Consiste...
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direct numerical simulation and analysis of a spatially evolving supersonic turbulent boundary layer at m 2 25
Physics of Fluids, 2004Co-Authors: Sergio Pirozzoli, Francesco Grasso, Thomas B GatskiAbstract:A spatially developing supersonic adiabatic flat plate boundary layer flow (at M∞=2.25 and Reθ≈4000) is analyzed by means of direct numerical simulation. The numerical algorithm is based on a mixed weighted essentially nonoscillatory compact-difference method for the three-dimensional Navier–Stokes equations. The main objectives are to assess the validity of Morkovin’s hypothesis and Reynolds analogies, and to analyze the controlling mechanisms for turbulence production, dissipation, and transport. The results show that the essential dynamics of the investigated turbulent supersonic boundary layer flow closely resembles the incompressible pattern. The Van Driest transformed mean velocity obeys the incompressible law-of-the-wall, and the mean Static Temperature field exhibits a quadratic dependency upon the mean velocity, as predicted by the Crocco–Busemann relation. The total Temperature has been found not to be precisely uniform, and total Temperature fluctuations are found to be non-negligible. Consiste...
Sergio Pirozzoli - One of the best experts on this subject based on the ideXlab platform.
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direct numerical simulation and analysis of a spatially evolving supersonic turbulent boundary layer at m 2 25
Physics of Fluids, 2004Co-Authors: Sergio Pirozzoli, Francesco Grasso, Thomas B GatskiAbstract:A spatially developing supersonic adiabatic flat plate boundary layer flow (at M∞=2.25 and Reθ≈4000) is analyzed by means of direct numerical simulation. The numerical algorithm is based on a mixed weighted essentially nonoscillatory compact-difference method for the three-dimensional Navier–Stokes equations. The main objectives are to assess the validity of Morkovin’s hypothesis and Reynolds analogies, and to analyze the controlling mechanisms for turbulence production, dissipation, and transport. The results show that the essential dynamics of the investigated turbulent supersonic boundary layer flow closely resembles the incompressible pattern. The Van Driest transformed mean velocity obeys the incompressible law-of-the-wall, and the mean Static Temperature field exhibits a quadratic dependency upon the mean velocity, as predicted by the Crocco–Busemann relation. The total Temperature has been found not to be precisely uniform, and total Temperature fluctuations are found to be non-negligible. Consistently, the turbulent Prandtl number is not unity, and it varies between 0.7 and 0.8 in the outer part of the boundary layer. Nonetheless, a modified strong Reynolds analogy is still verified. In agreement with the low Mach number results, the streamwise velocity component and the Temperature are only weakly anti-correlated. The turbulent kinetic energy budget also shows similarities with the incompressible case provided all terms of the equation are properly scaled; indeed, the leading compressibility contributions are negligible throughout the boundary layer.A spatially developing supersonic adiabatic flat plate boundary layer flow (at M∞=2.25 and Reθ≈4000) is analyzed by means of direct numerical simulation. The numerical algorithm is based on a mixed weighted essentially nonoscillatory compact-difference method for the three-dimensional Navier–Stokes equations. The main objectives are to assess the validity of Morkovin’s hypothesis and Reynolds analogies, and to analyze the controlling mechanisms for turbulence production, dissipation, and transport. The results show that the essential dynamics of the investigated turbulent supersonic boundary layer flow closely resembles the incompressible pattern. The Van Driest transformed mean velocity obeys the incompressible law-of-the-wall, and the mean Static Temperature field exhibits a quadratic dependency upon the mean velocity, as predicted by the Crocco–Busemann relation. The total Temperature has been found not to be precisely uniform, and total Temperature fluctuations are found to be non-negligible. Consiste...
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direct numerical simulation and analysis of a spatially evolving supersonic turbulent boundary layer at m 2 25
Physics of Fluids, 2004Co-Authors: Sergio Pirozzoli, Francesco Grasso, Thomas B GatskiAbstract:A spatially developing supersonic adiabatic flat plate boundary layer flow (at M∞=2.25 and Reθ≈4000) is analyzed by means of direct numerical simulation. The numerical algorithm is based on a mixed weighted essentially nonoscillatory compact-difference method for the three-dimensional Navier–Stokes equations. The main objectives are to assess the validity of Morkovin’s hypothesis and Reynolds analogies, and to analyze the controlling mechanisms for turbulence production, dissipation, and transport. The results show that the essential dynamics of the investigated turbulent supersonic boundary layer flow closely resembles the incompressible pattern. The Van Driest transformed mean velocity obeys the incompressible law-of-the-wall, and the mean Static Temperature field exhibits a quadratic dependency upon the mean velocity, as predicted by the Crocco–Busemann relation. The total Temperature has been found not to be precisely uniform, and total Temperature fluctuations are found to be non-negligible. Consiste...
Hongbing Ding - One of the best experts on this subject based on the ideXlab platform.
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performance of supersonic steam ejectors considering the nonequilibrium condensation phenomenon for efficient energy utilisation
Applied Energy, 2019Co-Authors: Yan Yang, Hongbing DingAbstract:Abstract Supersonic ejectors are of great interest for various industries as they can improve the quality of the low-grade heat source in an eco-friendly and sustainable way. However, the impact of steam condensation on the supersonic ejector performances is not fully understood and is usually neglected by using the dry gas assumption. The non-equilibrium condensation occurs during the expansion and mixing process and is tightly coupled with the high turbulence, oblique and expansion waves in supersonic flows. In this paper, we develop a wet steam model based on the computational fluid dynamics to understand the intricate feature of the steam condensation in the supersonic ejector. The numerical results show that the dry gas model exaggerates the expansion characteristics of the primary nozzle by 21.95%, which predicts a Mach number of 2.00 at the nozzle exit compared to 1.64 for the wet steam model. The dry gas model computes the Static Temperature lower to 196 K, whereas the wet steam model predicts the Static Temperature above the triple point due to the phase change process. The liquid fraction can reach 7.2% of the total mass based on the prediction of the wet steam model. The performance analysis indicates that the dry gas model over-estimates a higher entrainment ratio by 11.71% than the wet steam model for the steam ejector.
Guangming Chen - One of the best experts on this subject based on the ideXlab platform.
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experimental study of the energy separation in a vortex tube
International Journal of Refrigeration-revue Internationale Du Froid, 2015Co-Authors: Nan Li, Zhiyuan Zeng, Zheng Wang, Guangming ChenAbstract:Abstract A vortex tube is a simple-structure device which can separate a compressed stream into a hot and a cold stream. The accurate flow pattern inside the vortex tube remains elusive and no satisfactory explanation of its energy separation mechanism has been put forward yet. In this work, the influences of inlet pressure and cold mass fraction on the performance of the vortex tube were explored. The experimental results show that the Static Temperature in the center of vortex tube is higher than that of the peripheral part. Besides, the stagnation point inside the vortex tube moves to the cold end with the decrease of the inlet pressure or the increase of the cold mass fraction. This paper also tries to present an explanation for the maximum cooling effect and the maximum heating effect when the cold mass fraction is about 0.3 and 0.8, respectively.
Xianggeng Wei - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of flame structure and combustion mode in a hydrogen fueled supersonic combustor
International Journal of Hydrogen Energy, 2015Co-Authors: Zhiwei Huang, Fei Qin, Xianggeng WeiAbstract:Abstract In this study, Large Eddy Simulation (LES) of supersonic turbulent mixing and combustion adopting a Partially Stirred Reactor (PaSR) sub-grid combustion model is performed for a hydrogen fueled model scramjet combustor. The compressible LES solver, which adopts a skeleton of 27 steps and 9 species hydrogen chemical kinetics model, is used to simulate the flowing and combustion processes based on structured hexahedral grids. The code is implemented in an Open Source Field Operation and Manipulation (OpenFOAM) solver, and validated against experimental data in terms of mean axial velocity and Static Temperature at different cross-sections, all show good predictions. An analysis of the flow field is carried out to investigate the supersonic turbulent flame structure and combustion mode in the combustor. Mixture fraction is extracted to indicate the reaction progress at different sites, which donates the most likely flame locations when at stoichiometric. Comparison of combustion parameters including OH mass fraction, scalar dissipation rate, flame index and heat release rate spatial distribution reveals that the supersonic combustion has the characteristics of a turbulent diffusion flame, where combustion is held at non-premixed mode controlled by turbulent mixing in the shear layers. A time scale analysis, the Damkohler Number is performed to examine these reactive zones in more detail. The role of auto-ignition in flame stabilization and lift-off is revealed.
