Reentry Simulation on CMC Materials.

Abstract

One of the main topics of investigating reentry bodies is the evaluation of heat protection systems, especially the choice and development of proper materials. The reentry process takes place in hypervelocity flow fields of thermodynamic nonequilibrium which are connected with complex interaction between chemical processes in the high temperature air and others at the surface of the heat protection material. The arc-heated wind tunnel LBK of DLR is one of the few existing high energy facilities for testing thermal protection materials with realistic gas surface interactions over times sufficient for stationary test conditions. Tests with samples arranged in the stagnation area of models give the possibility to consider the reaction of the thermal protection material dependent on the enthalpy, the surface pressure and the nonequilibrium conditions of the flow field. The reaction is identified by measuring the surface temperature, the mass loss rate and the change of the material thickness. Additional to these integral measurements investigations are made with a scanning electron microscope over the cross section of the sample to indicate the species distribution, especially the depth of penetration of the O-species into the probe. The flat plate tests give information about the dependence of the temperature field at the surface from the different sample materials. The temperature distribution at the surface indicates the distinguishable catalytic efficiency of the material.