Gas-Surface Energy Exchange Characterization Around a Cone in the Free-Piston-Driven Shock Tunnel

Abstract

This work describes numerical and experimental research in the Indian Hypersonic Shock Tunnel 3 on a blunt cone model and related computation of the facility parameters: nozzle reservoir conditions, nozzle transit time, and freestream conditions. Specialized codes accounting for real gas effects and nonequilibrium are used to obtain facility parameters. Starting at freestream conditions, a physicochemical model is developed in Fluent to simulate the dissociating environment within the shock layer over the model, assuming thermodynamic equilibrium. The model is validated, then invoked with a surface reaction of exothermic chromium oxidation, to study model erosion and gas-surface energy exchange. A mathematical analysis is performed to estimate surface oxidation rate, heat release, and its effect on shock layer temperature and aerodynamic heating. Both the quantities show considerable increase. Experimental measurement of surface heat flux and temperature using thin film gauges and two-color ratio pyrometry, respectively, also show an increase. The Fluent model with an iterative technique is used to show that the actual temperature at stagnation point is about 90 K higher than its counterpart based on line-of-sight averaged measurements. Finally, analytical calculations are performed to obtain the reaction rate parameter as a measure of the degree of dissociation in the shock layer.