Film Cooling of a Blunt Body in Supersonic High Enthalpy Flows

During atmospheric re-entry at hypersonic speed or at very high speed flight in the atmosphere, vehicles experience extremely high thermal loads for relatively long times: the classical thermal protection materials do not survive and need to be replaced by lightweight actively cooled components. This work investigates experimentally film cooling of a blunt body in a supersonic high enthalpy flow. The coolant, injected in the stagnation zone of the blunt body surface against the free stream, operates as a thin, cool, insulating layer, yielding a thickening of the boundary layer, thus reducing the temperature gradient of the surface. The experiments were performed in the Aerothermodynamics Laboratory in the Technion, where a plasma arc tunnel enables simulation of high enthalpy flows. Two models (with and without injection) were exposed to a Mach 2.2 freestream with a total enthalpy of 1.7 MJ/kg. Nitrogen and helium were used as coolant gases. A parametric study shows the influence of coolant physical properties and mass flow rate on the characteristics of the flow surrounding the model and on the resulting temperature reduction at different locations on the test model.