A Computational Model To Characterize Different Flow Regimes For Microscale Re-entry Satellites

Abstract

Atmospheric re-entry vehicles experience different flow regimes during flight due to the change in atmospheric density along the re-entry trajectory. This change in density creates non-equilibrium regions on the order of mean free path, called Knudsen layer. In the design of atmospheric re-entry vehicles, the flux variations near the wall of the re-entry vehicles are of critical importance. Traditional CFD simulations that use Navier-Stokes equations fail to predict the flow in the Knudsen layer. The Direct Simulation Monte Carlo (DSMC) method is accurate for all flow regimes, and correctly models the Knudsen layer but is computationally expensive. The computational cost increases as the number of molecules simulated increases. The areas where the rarefaction effects begin to dominate can be quantified by a Knudsen breakdown parameter (Kn). Traditional CFD can be improved with the use of slip boundary conditions in regions where the Knudsen breakdown parameter predicts the failure of continuum regime. In this thesis, a computational model has been developed to extend the validity of the continuum formulation with slip boundary conditions. The model uses the no-slip boundary conditions for continuum regime (Kn<0.01), and Maxwell-Smoluchowski slip boundary conditions for slip regime (Kn<0.1) in the free stream atmospheric properties. The results demonstrate the validity of the unified model in continuum and slip regime. For specific Knudsen number, flow predictions were validated against results from DSMC. The flow results matched within 10%.