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Combustion Systems
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Now, the other type of mixing, that is, normal mixing, is discussed. One of the simplest approaches is the transverse (normal) injection of fuel from a wall orifice. As the fuel jet interacts with the supersonic cross flow, an interesting but rather complicated flow field is generated. Figure 10.23 illustrates the general flow features of an under-expanded transverse jet injected into a cross flow. As the supersonic cross flow is displaced by the fuel jet, a 3-D bow shock is produced due to the blockage produced by the flow. The bow shock causes the upstream wall boundary layer to separate, providing a region where the boundary layer and jet fluids mix subsonically upstream of the jet exit. This region, confined by the separation shock wave formed in front of it, is important in transverse injection flow fields owing to its flameholding capability in combusting situations.
A Finite Volume Chimera Method for Fast Transient Dynamics in Compressible Flow Problems
Published in International Journal of Computational Fluid Dynamics, 2021
Alexis Picard, Nicolas Lelong, Olivier Jamond, Vincent Faucher, Christian Tenaud
When the moving front shock wave interacts with the cylinder, a peak on the pressure drag force occurs, followed by a relaxation period during which the front shock wave comes established as a bow shock in front of the cylinder. Then a steady state solution occurs. Whatever the grid spacing is, a statistically converged steady state solution is achieved from at most a dimensionless time , with however the finer the grid, the greater this time occurs. As we can see, for the coarsest grids the drag force converges towards a constant value while for the finer grids oscillations around a converged value appear due to the high resolution of the cylinder wake. Compared to the single grid computations, the Chimera method gives comparables results on the drag force while some weak discrepancies can be recorded for the coarsest grids. Very similar results have however been recovered for the finest grid tested with the Chimera method. By zooming in on the steady state region between dimensionless times 40 and 52.5 as shown in Figure 16, we can see that the average force seems to converge toward the value N. We can observe that the Chimera case captures oscillations around the cylinder with a coarser grid refinement than the single grid configuration. Considering that grids between the single mesh case and the Chimera case are similar but not identical, differences might be caused by a difference in the grid resolution as well as a better grid regularity of the mesh in the Chimera case.
The p-Weighted Limiter for the Discontinuous Galerkin Method in Solving Compressible Flows on Tetrahedral Grids
Published in International Journal of Computational Fluid Dynamics, 2021
The first case is the inviscid flows with inlet Mach number and 3, angle of attach (AoA) The DG schemes of order p = 1 and 3 are applied. One can find the experimental data for such inlet Mach number in Gray (1964). The calculation results are shown in Figures 21 and 22. The shock region marked by the m-KXRCF detector indicates that the scheme can single out much more troubled cells around the bow shock and the expansion/compression corners. The bow shock wave is well captured in high resolution without carbuncle phenomenon. The p = 3 scheme gives thinner thickness for the discontinuities. The comparison shown in Figure 23 shows that the numerical results come very close to the experimental data.
Application of Gas-Kinetic Scheme for Continuum and Near-Continuum Flow on Unstructured Mesh
Published in International Journal of Computational Fluid Dynamics, 2022
Guang Zhao, Chengwen Zhong, Sha Liu, Yong Wang, Congshan Zhuo
It can be seen from the solution contours of pressure: Figures 18(a), 19(a) and 20(a); temperature: Figures 18(b), 19(b) and 20(b) predicted by DUGKS and GKS with kinetic boundary condition match well in all three Knudsen numbers. A bow shock wave in front of the cylinder, the smaller the Knudsen number, the thinner and steeper the bow shock wave will be obtained. With the Knudsen number increase from 0.0001 to 0.01, large physical dissipation will thicken the shock, the bow shock in front of the cylinder becomes much more diffuse.