DSMC modeling of rarefied aerodynamic features for Lunar exploration re-entry vehicle

As the Lunar exploration re-entry vehicle returns to the atmosphere, it experiences violent thermo-chemical nonequilibrium phenomenon and causes important impact on its aerodynamic features. The ground test facilities can hardly simulate the real gas effects in the low density circumstance and expense costly. The aerothermodynamics and flow structures of Chinese Shenzhou like capsule are numerically simulated under different re-entry speeds, using the direct simulation Monte Carlo (DSMC) method. A hybrid grid structure of Cartesian coordinate meshes and surface unstructured triangular cells is adopted. More precise collision and sampling cells during the self-adaption procedure based on local flow gradient variation are used to improve the spatial precision. Temperature dependence of rotational and vibrational collision numbers with Larsen-Borgnakke energy exchange model and Total Collision Energy (TCE) chemistry model are included. Parallel DSMC code is developed based on the static random load balance technique using MPI message passing scheme for communication between processors. Results show that the rarefied gas effect has great impact on the lift-drag ratio and trim characteristics, and the high temperature real gas effect affects the surface thermal environment significantly. Moreover, at the Lunar return velocity, strong dissociation reactions occur in rarefied conditions at 100km.