Entry Capsule Heatshield Transpiration Cooling Effects Observed in Boundary Layer

Transpiration cooling as means of thermal protection for atmospheric entry capsules will involve the injection of mass and energy into the boundary layer. The effects of these downstream are subject to influence flow transition and effective aerodynamic characteristics. To evaluate these, a transpiration cooling system is approximated computationally by application of source terms of transpiration products at the surface cells of a selected region towards the windside shoulder of the capsule heatshield. Various cooling blowing rates are simulated and evaluated for their impacts. Results analyze boundary layer profile, values of shear stress and species mass fractions at the wall, and momentum thickness Reynolds number as measure of estimated transition. These are compared among an array of blowing rates for impact on and downstream of the source term injection site. Laminar results indicate transition likely over most of the higher injection rates, and need for turbulent modelling at and downstream of the injection surface.