Computation of rarefaction effects on a blunt body in hypersonic flow

High-speed vehicles such as next generation launch vehicles or reusable spacecraft experience different flow regimes during flight due to change in atmospheric density. At high altitude, due to low density the flow becomes rarefied and the rarefaction effects cannot be accurately modeled by the Navier-Stokes equations with no-slip boundary conditions. In low density flow, for predicting the small rarefaction effects, Maxwell suggested the use of slip boundary conditions with Navier-Stokes equations. In this paper, a UDF (User Defined Function) which employs the velocity slip and temperature jump boundary conditions at the wall is applied to the commercial flow solver ANSYS FLUENT with the compressible Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with the Shear-Stress-Transport (SST) k-ω turbulence model to simulate the flow around a blunt body in hypersonic flow. The results of both no-slip condition and slip boundary conditions for flow past an axisymmetric body with Knudsen number Kn = 0.0003354, 0.00838, 0.0167, 0.0418, and 0.1are computed and the effect of rarefaction on heat transfer and drag is analyzed and discussed. In addition, a multi-objective genetic algorithm is used to optimize the shape of the blunt body for minimizing both the drag and heat flux. A Pareto optimal front is obtained for different optimization weights of drag vs. heat transfer for Kn = 0.0167.