Numerical Simulation Of Square Cavity Flow And Jet Flow Based On Gas Kinetic Scheme

Gas kinetic scheme（GKS）is an emerging computational fluid dynamics（CFD）numerical method guided by mesoscopic gas kinetic theory.GKS exhibits good robustness and stability at the full speed,and is the hot point of the current CFD frontier research.The lid-driven square cavity flow is a classic example in CFD.Supersonic free jets are ubiquitous in the aerospace field,and the hydrostatic lubrication flow field formed by the impinging jet is the key to the study of gas lubrication.In this thesis,the gas kinetic scheme is used to numerically simulate the cavity flow and jet problem and discuss the characteristic changes of the flow field.The main research work is as follows:First of all,using structured rectangular grids and ghost cell boundary conditions,a collisionfree first-and second-order kinetic vector flux scheme（KFVS）and a second-order gas with collision term were established under the guidance of gas kinetic theory.Using the Riemann problem as the numerical verification,the second-order gas kinetic scheme had better accuracy and stability than KFVS.Then,the incompressible and low Mach number two-dimensional lid-driven square cavity was calculated based on the gas kinetic scheme,and the flow field distribution of the cover-driven square cavity with different Reynolds numbers was calculated,and the results were consistent with the calculation results of Ghia.The influence law of different cover driving modes on the flow field distribution of the lid-driven square cavity with corner obstacles was discussed.It can be obtained that the secondary vortex of the unilaterally-driven flow field with corners increases,and the flow field distribution of the two-sided same-direction driving mode presents Bifurcation phenomenon,the entire flow field was symmetrical about the geometric center in the bilateral reverse drive mode,and most of the gas in the square cavity maked a smooth circular motion around the primary vortex.Secondly,the two-dimensional supersonic free jet under high Reynolds number was calculated using the gas kinetic scheme,which clearly captured the Prandtl–Meyer expansion fan,jet shear layer and vortex-guided shock wave in the jet flow field and the key characteristics of the flow field such as pair,diaphragm shock and so on.The flow field distribution of the main flow field parameters of the jet flow field at a certain time node was given,and the variation of the characteristic parameters on the vortex ring of the jet flow field with time was analyzed,and the plane jets under different pressure ratios were calculated.The evolution law of the vortex ring in the flow field under different pressure ratios was discussed.Finally,the simulation study of the aerostatic pressure lubrication flow field was carried out,and the throttling characteristics were expounded with the small hole type aerostatic pressure bearing as the research object.The distribution law of the lubricating flow field under different air supply pressures was calculated,Compared with the calculation results of CFD commercial software,it was found that the high-pressure gas emitted from the orifice hits the part of the guide rail surface,and there was a backflow phenomenon.The compressible high-pressure gas did not expand rapidly at the orifice,which was the key to the formation of gas lubrication between the rail surface and the bearing surface.In summary,this thesis provides numerical solutions to typical problems in the field of fluids based on the gas kinetic theory.The distribution laws of square cavity flow and jet flow field provide scientific guidance for practical engineering applications.Self-programmed numerical simulation instead of commercial software simulation has far-reaching academic theoretical value.At the same time,these works have laid a good foundation for improving the higher-order scheme of the gas kinetic scheme and exploring the three-dimensional flow field distribution in the future.