Observation of hypersonic high-enthalpy boundary layer with gaseous injection

Abstract

Transpiration cooling at hypersonic high-enthalpy real-gas flow was experimentally studied in the free-piston shock tunnel HIEST. Heat flux distribution on a flat plate of 1000 mm length was measured, which has an injector made of porous material. The material was permeable C/C, through which gaseous Helium was injected to the plate surface. To adjust unit Reynolds number to almost 2E6/m, which is the critical Reynolds number for transition, test free-steam condition was fixed; stagnation enthalpy was 8 MJ/kg and free-stream Pitot pressure was 200 kPa and unit Reynolds number 2E6/m. Changing of plenum chamber pressure, flow rate of gaseous helium as injectant was changed from 0 to 5 g/s. The measurement showed that the injection was effective to reduce surface heat flux downstream of injector, however, excessive injectant flow rate caused early onset of boundary layer transition, which increase higher heat flux rather than that of no-injection.