Testing of the EXPERT Thermal Protection System Junction in a Plasma Wind Tunnel

Abstract

The European Space Agency EXPERT vehicle thermal protection system is composed of a ceramic nose and a metallic body skirt, such that a transition in the recombination efficiency occurs when the plasma flow travels across their junction during the reentry phase. In this situation a heat flux jump is experienced between the two materials and has to be carefully handled for a safe vehicle design. Ground experiments in the induction-coupled plasma wind tunnel of the von Karman Institute are performed, in order to simulate this flight phenomenon. Three probe models (low catalytic, high catalytic and combined low-high catalytic) are tested and the temperature distributions over the samples are measured by means of infrared techniques. An experimental proof and a quantification of the transition are provided. Air recombination coefficients for the material studied are determined under typical flight conditions. Nomenclature h = enthalpy per unit mass, J kg -1 m = mass flow rate, kg s -1 P = pressure, Pa P W = power, W q = heat flux, W m -2 R = radius, m T = temperature, T x = surface parallel coordinate, m y = surface normal coordinate, m u = velocity x-component, m s -1 v = velocity y-component, m s -1 r = reflectivity ε = emissivity γ = catalycity β = velocity gradient, s -1 σ = Stefan-Boltzmann constant 5.67 × 10 -8 W m -2 K -4 λ = wavelength, m k = thermal conducivity , W m -1 K -1 J = diffusion flux, kg m -2 s -1 n = number of chemical species Subscript cw = cold wall w = wall s = static d = dynamic p = at constant pressure in = inlet out = outlet e = boundary layer edge f = flight 0 = initial i = chemical species ref = reference cond = conductive c = conductive d = diffusive r = radiative sp = stagnation point Superscript exp = experimental

3D infrared temperature maps measurements of ablative materials during plasma wind tunnel experiments

“…Notably, Hellstein and Szwedo [19] combined a 3D scanner with IR thermography for realtime reconstruction of 3D temperature maps in non-destructive testing of composite structures. However, application of such techniques to PWT experiments is scarce in the literature: radiometers are typically used to measure temperature around the stagnation point [20,21] while IR thermography, lacking a spatial calibration, usually provides only some qualitative information from the 2D image [22][23][24][25][26]. Hence, 3D temperature maps reconstruction is highly desirable to provide accurate and spatially calibrated measurements.…”