Study of shock-shock interactions in rarefied flows using direct simulation Monte Carlo method

The majority of studies on shock-shock interactions assume the inviscid or high-Reynolds-number condition for the fluid flows. However, the rarefied flows encountered by the hypersonic vehicles in their high-altitude flights require investigation that considers both the shock-shock interaction and the rarefied gas effect. An in-house direct simulation Monte Carlo (DSMC) solver is employed to simulate a series of hypersonic air flows over a wedge-cylinder configuration at the freestream Mach number of 10. The DSMC simulations cover 15 different Knudsen numbers Kn _∞, spanning from 6.688×10⁻³ to 6.688×10⁻¹. At the lowest Knudsen number, the numerical results are validated by the corresponding wind-tunnel experiment and demonstrate the features of an Edney type IV shock-shock interaction, including the type IV wave pattern, the supersonic jet impingement, the amplifications of surface shear stress, pressure, and heat flux, as well as the shifts in the angular positions of the peak shear stress, pressure, and heat flux over the cylinder surface. In ascending order of Kn _∞, the flow fields over the wedge-cylinder configuration and the undisturbed cylinder are simulated in detail. In addition, the distributions of shear stress, pressure, and heat flux on the surface of the cylinder are calculated and analyzed. The increase in flow rarefaction continuously alters the flow pattern of the shock-shock interaction, in which the wave system gradually loses the ability to deflect the streamlines or to concentrate the energy in the flow. As flow becomes more rarefied, the shock-shock interaction will result in smaller amplification factors and smaller angular shifts of the maximum aerodynamic/aerothermal loads. At the highest Kn _∞ in this study, the amplification factors for skin friction and heat flux are found to be less than unity. The existence of the supersonic jet and its position relative to the cylinder account for the distribution characteristics of aerodynamic/aerothermal loads over the cylinder surface.