Heat Balance for a Transpiration-Cooled Heat Shield Experiment in a Shock Tube

Abstract

SHEFEX II is a DLR-project that aims to prove the feasibility of the sharp edge configuration for hypersonic flight. Its name stands for Sharp Edge Flight Experiment. One key experiment of the SHEFEX II is AKTiV, which consists of a transpiration cooling system for the thermal protection system (TPC) by means of nitrogen flowing throughout a porous material. The active cooling for TPS is a new concept that has never been tested before in real flight. In order to predict the cooling efficiency, DLR developed the tool HEATS. HEATS is a program that solves transient heat balances in two dimensions. During the SHEFEX II testing campaign in Göttingen, a reduced scale model of SHEFEX II was tested in HEG and heat flux data were measured for several angle of attack and coolant mass flow rates through the AKTiV experiment. HEG is a major ground test facility that reproduces the flow conditions from atmospheric re-entry. In order to achieve the same flow conditions in HEG as in flight, the air density parameter was adjusted. However, this resulted in the transfer in HEG being different from the one occurring in flight. This work focuses on the techniques used to predict the SHEFEX II heat transfer in a ground test facility. The results are validated by means of HEG measurements and CFD computations. HEATS is first verified and validated to ensure integrity of the simulations. While cooling, the heat flux behavior downstream the AKTiV experiment of the model is discussed. The overall validation of HEATS is satisfactory with deviations of approximately 20%. Finally, relations to extrapolate the heat transfer from HEG conditions to flight are given for the cases of aerodynamic heating as well as for cooling. A relation was found for the equivalent amount of coolant to use in HEG that will give the same cooling rate as in flight.