Navier-stokes and direct simulation Monte Carlo predictions for laminar hypersonic separation

Axisymmetric direct simulation Monte Carlo (DSMC) and Navier-Stokes simulations are performed as part of a code validation effort for hypersonic flows. The flowfield examined herein is the Mach 11 laminar flow over a 25-55-deg blunted biconic. Experimental data are available for surface pressure and heat flux at a Knudsen number Kn = 0.019 based on the nose radius. Simulations at a reduced freestream density (Kn = 0.057) are performed to explore the region of viability of the numerical methods for hypersonic separated flows. A detailed and careful effort is made to address the numerical accuracy of these simulations, including iterative and grid convergence studies for Navier-Stokes and temporal, grid, and particle convergence studies for DSMC. Good agreement is found between the DSMC and Navier-Stokes simulation approaches for surface properties as well as velocity profiles within the recirculation zone for the reduced density case. The results obtained indicate that the failure of earlier DSMC simulations at Kn = 0.019 is due to insufficient grid refinement within the recirculation zone. Furthermore, it is shown that accurate simulations of the biconic at the experimental conditions with the DSMC method are not yet possible due to the extreme computational cost.