Research On The Mechanism Of Hypersonic Slip Flow

Rarefied gas effects have to be considered when doing the research and design of hypersonic flight vehicle in near space, in which accurate prediction of flow field and surface properties such as pressure, shear stress and heat flux are needed. Research on the mechanism of hypersonic slip flow must consist of mathematical analysis, numerical analysis and experimental research, and is of great importance resently. The research presented here in this dissertation has four main parts: CFD code debuging, mathematical model analysis, numerical analysis and experimental programming, which are detailed as follows:The comparison of advantage and disadvantage among molecular method, continuum method and hybrid method on the hypersonic slip flow research are carried out, which points out that the N-S equation with slip bouindary model can get the satisfied accurate prediction while the computational cost is less expensive, and the code development relatively easy. This research developed a general 3D, parallel, structurted, finite-volume CFD code based on 3D N-S governing equations, using M-AUSMPW+ scheme and LU-SGS implicit time integration scheme. The comparison with experimental data, verified the code accuracy.The main slip models are derived and analysed in detail, then the numerical experiments are presented to find out that the improved Maxwell model is relatively accurate and efficient. The hypersonic slip flow heat flux model are derived from both molecular level and hydrodynamics level, the additional term in the improved model are definite: from the microscopic view, it shows the whole energy transferred to the soild surface unit time and area due to the molecular collision, from the macroscopic view, it denotes the energy transferred by shear stress unit time, and the magnitude analysis indicates that the additional term can not be neglected. This heat flux computational model in some sense improves the numerical results. The progress and status reporting of gas/surface accommodation coefficients are presented as a guide of which typical values to choose for this research. The research on hypersonic slip flow grid effect for air heating problem are carried out, the results reveals that in slip flow, the accommodation coefficients have little impact on heat flux convergence which can be obtained using 1-2 grid Renold number. Through the comparison with two hypersonic slip flow experiments, the accuracy of computational model derived above are examined and certified.The typical body of hypersonic flight vehicle such as 2D cylinder, 3D sphere, sharp-leading edge and zero-thickness flate plate are used in numerical analysis, and the hypersonic slip flow field properties and surface properties distributions (pressure, shear stress and heat flux) are simulated: Choose three typical values 0.5, 0.75 and 1.0 to study the effect of accommodation coefficients. The Mach number effects in slip flow are considered. Choose four typical Knudsen number, 0.002, 0.01, 0.05 and 0.25 to deeply study the regulations among slip flow regime. The reseach reviews that, the shock layer gets thicker when the Knudsen number becomes bigger, the shock discontinuous effects are getting weaker and the shock strength is weakened gradually. The rise of Mach number makes the rarefied gas effects stronger. The correlation between accommodation coefficients and viscous effects are found out, and the rise of the accommodation coefficients strengthen the viscous effects which weaken the rarefied gas effects. Then, research on the high space large mach number chemical-equilibrium slip flow are presented and indicate that in hypersonic slip flow regime, chemical-equilibrium effects make the shock layer thinner, pressure rise and temperature lower, the surface heat flux coefficient and slip velocity get smaller in which this trend becomes stronger as the Knudsen number rise.The advancement of experimental research on hypersonic rarefied gas flow are summarized, and point out from flow field and gas/solid surface view the aspects that need to be examined in experiment, in other words, that difficult to calculate, and give detailed discreption on planar induced iodine fluorescence. On the basis above and the guide of mathematical analysis as well as numerical nanlysis, a preliminary programming for experimental environment on hypersonic slip flow are presented which integrates the flow field visualization, velocity and temperature measurement and gas/sueface interaction research, forming the small-size systemic blueprint for research on hypersonic slip flow.