Numerical Simulation of Massively Separated Flow over a Model of the Apollo Command Module

Abstract

The problem of a three-dimensional massively separated flow behind the Apollo capsule in a supersonic flow at different angles of attack is studied computationally using the general purpose CFD code ANSYS Fluent. Density-based and pressure-based coupled solver formulations are considered. Steady-state and transient solutions are compared. The SST k- turbulence model is employed to simulate turbulence effects in steady-state cases. In addition, the SST transition model is applied to investigate the importance of transitional effects in steady-state. The Scale-Adaptive Simulation (SAS) model is applied to compute transient solutions. This unsteady turbulence model introduces Von Karman length-scales to dynamically adjust to the resolved structures in the flow field, which produces LES-like results for sufficiently resolved computational domains in space and time, and it reverts to a RANS solution otherwise. The near-wall mesh is fine enough to resolve the viscosity-affected near-wall region all the way to the laminar sublayer. Second-order upwind discretization is used in steady state, and a higher-order central differencing scheme for the momentum equation is applied in the transient set-up. A mesh refinement study on three meshes (two hexahedral and one Cut-Cell Cartesian) is carried out. The transient SAS solution on the Cut-Cell mesh is found to be the most accurate, as it captures the unsteady vortex shedding phenomena behind the capsule, and predicts the drag coefficient within 1.6% of the experimental data 1