Arc Jet Testing of CMC Samples with Transpiration Cooling

Abstract

High speed sustained atmospheric flight creates high thermal loads at the tip, leading edges, intake ramps or engine structures of a flight vehicle. However, sharp edges are mandatory for these vehicles in order to obtain the required aerodynamic performance. To provide technical solutions for these problems, the concept of using porous ceramic matrix composite (CMC) materials in combination with active cooling by transpiration was investigated. An arc jet test campaign was carried out to determine basic parameters in terms of minimum required coolant focusing on liquid water as the coolant media. The tests were stagnation tests on flat samples with a diameter of 50 mm. The front wall thickness was 8 mm. The tests were carried out in the L3K and L2K arc jet facilities of DLR Cologne at approximately 1 MW/m² heat load. Good results were achieved in terms of mass flow data for C/C samples. A number of tests could be carried out at low supply pressures and low mass flow. A medium value of the lower limit mass flow is 0.33 g/s at a pressure of 225 hPa which is equal to 0.152 kg/m²s. With aluminum oxide samples, a cold surface could also be maintained, however, it was not possible to establish a steady-state condition in terms of mass flow and supply pressure.