Computational Evaluation of Aero-Thermo-Dynamic Loads and Effect of Catalyticity in an Arc-Jet Wind Tunnel

With a view to designing tests in the arc wind tunnel Small Planetary Entry Simulator (SPES) at the Department of Industrial Engineering of the University of Naples "Federico II" on specimens of Ultra-High-Temperature Ceramic (UHTC) materials, computer simulations have been carried out in order to get information about the test conditions, i.e. electrical power supplied to the torch, the nozzle area ratio (exit area/throat area) and the specimen geometry, in order to avoid expensive and time-consuming experimental characterization. Computations have been carried out both by a Computation Fluid-Dynamics (CFD) and a Direct Simulation Monte Carlo (DSMC) code. The computations provided important, quantitative information about flow field as per velocity, temperature, gas composition, etc. and about heat flux and pressure on the specimen. The present computations allowed the authors to define the capabilities of SPES to perform tests on UHTC specimens, identifying a range of potential applications. Computed values of heat flux have been also compared with preliminary measurements performed by means of a copper slug calorimeter. Due to the evident effect of surface catalytic level on the experimental measurements, an experimental/computational procedure has been used to estimate the recombination efficiencies of oxygen and nitrogen on the calorimeter surface. The definition of this procedure is aimed at a future evaluation of surface catalyticity of UHTC specimens. At the conditions tested in the present paper, the procedure indicates that oxygen catalytic effect is higher than that of nitrogen, in agreement with what reported in literature.