Large Eddy Simulation Of Under-expanded Supersonic Impinging Jet

Under-expanded supersonic impinging jets are widely used in many engineering fields, such as those occurring in the next generation of vertical or short take-off landing aircraft, the rocket launch, and the removal of dust and water, et al. Supersonic impinging jet also has complicated structures, which interact with each other. So the study of supersonic impinging jets has its industrial applications and academic significance.Large-Eddy Simulations (LES) of under-expanded supersonic jet impinging on large plate have been carried out. The Favre-filtered Navier-Stokes equations in cylindrical coordinate have been solved using a finite-difference method. The LES code employs five-order WENO for the convective fluxes, a fourth-order centered difference approach for the viscous fluxes and a four-stage third-order Strong-Stability-Preserving Runge-Kutta technique in time. The compressible Smagorinsky subgrid-scale (SGS) model is used for representing the effects of the unresolved scales on the resolved scales. The calculations have been performed on a multi-core computer using message-passing interface (MPI). Comparisons are made with experimental measurements of jets at the similar flow conditions. The result of which are reliable and encouraging.The numerical simulation successfully captures the shock wave structure in the jet plume and vortex structures with different scales in the internal and external shear layer and in the wall jet. The numerical results show the oscillation of the mach disk, and occurrence and disappearance of the annular shock in the peripheral supersonic flow during a period of oscillation.Through the numerical simulation, the evolution of the vortex in the internal shear layer has been observed. The numerical results show that the formations of large-scale vortex structures associate with the oscillation of the Mach disk. As the Mach disk oscillates axially to the most downstream, the vortex structures begin to roll up behind the Mach disk, and then propagate downstream and enlarge themselves as large structures. When the vortex structures impinged on the wall, most of the broken vortex structures begin to move with the wall jet. The rest moves to the recirculation zone. As the second annular shockwave eventually moves close to the impinging plate, the radial movement of vortex structure along the plate is inhibited. It is under the impact of internal and external shear layer that the interlacing vortex structures in the wall jet are formed.In the fluctuating velocity field, there are second vortex structures with reverse swirling relative to the main vortex. Pronounced velocity fluctuations occur in the wall jet outside of the recirculation zone as a result of the motion and collapse of the vortex structures in the two shear layers.After carefully analyze, it is revealed that there exists certain relationship among the oscillation of the mach disk, the appearance and disappearance of the oblique shock, the evolution of the vortex, and the impinging tone.