Measuring the Concentration of Freestream Species on a Hypersonic Transpiration-Cooled Stagnation Point

Abstract

This paper presents direct surface concentration measurements of a transpiration cooled stagnation point in hypersonic flow. Pressure sensitive paint (PSP) is employed on a porous alumina sample to measure the concentration of freestream species and thus how well the coolant mitigates mass diffusion from the freestream to the surface. Experiments are conducted at Mach 6.9 at three different Pitot pressures: 10 kPa, 20 kPa and 30 kPa. Porous alumina is chosen due to its ability to bond PSP and its similar microstructure to porous Ultra-High-Temperature Ceramics. Nitrogen, Argon and Krypton are used as injection gases at mass flow rates ranging

Oxidation Response of Transpiration-Cooled ZrB2 on a Hypersonic Stagnation Point

“…This diffusion is strongly dependent on the material microstructure. By not accounting for the adverse pressure gradient, the model will overpredict oxidation for the blowing cases [11]. It thus provides a conservative estimate of the oxidation protection provided by mass injection.…”

“…Upon exiting, the coolant forms a protective film that reduces part of the aerothermal heating [9] and catalytic heating [10]. Additionally, the film reduces the mole fraction of freestream oxygen at the surface [11].…”

Numerical Simulation of Transpiration Cooling on Stagnation Line in Thermochemical Non-Equilibrium

“…TC operates by injecting a coolant through a porous patch of the surface that requires cooling. TC cools the surface by 1) convection of a relatively cold coolant through the porous layer; 2) displacing the hot external stream in proximity of the surface and reducing the temperature gradient; 3) inhibiting surface reactions which contribute to the overall heat flux [1]. According the selection of the coolant mixture, TC can also be beneficial as an oxidation management method, as it can displace oxygen away from the surface.…”

“…While drag has been shown to change only slightly [2], risk of boundary layer blowoff may reduce the aerodynamic advantages of a sharp leading edge. Performance data on transpiration cooling devices in hypersonic environments have been obtained for a range of applications, including stagnation line heating [1]. Testing of cooling devices is however limited in scope because of the difficulty of either achieving realistic free stream enthalpies or Reynolds numbers or of obtaining data at realistic surface temperatures in transient facilities.…”