Abstract
This paper presents the performance of pressure-sensitive paint (PSP) for the direct measurement of species concentration on a porous surface with mass injection. It is used to measure the ability of an injected gas to reduce the mass transfer of freestream species to the surface. A porous alumina sample was sprayed with a PSP luminophore solution. The sample was installed into a flat plate model and exposed to hypersonic cross-flows in the Oxford High-Density Tunnel. Tests were conducted with no coolant injection, air injection, and nitrogen injection at increasing blowing ratios. Oxygen partial pressure maps on the transpiration-cooled surface were obtained for several conditions at unit Reynolds numbers between 2.58{-}5.0 times 10^7/ mathrm{m} and blowing ratios between 0.016{-}0.078%. The oxygen pressure decreases as the unit Reynolds number decreases and the blowing ratio increases.Graphic abstract
Highlights
Transpiration cooling is an active thermal protection system with the potential to be useful for aerospace applications in high-speed vehicles, rocket nozzles and future turbine components
Tests were conducted in the Oxford High Density Tunnel (HDT) (McGilvray et al 2015), using a flat plate model with a porous alumina insert
The O2 partial pressure can be converted into O2
Summary
Transpiration cooling is an active thermal protection system with the potential to be useful for aerospace applications in high-speed vehicles, rocket nozzles and future turbine components. A coolant is fed through a porous wall and forms a protective film upon exiting. This coolant film acts as a barrier against the hot freestream, thereby reducing the aerothermal heating (Ifti et al 2018). In high-enthalpy environments, the film mitigates catalytic heating and surface oxidation by inhibiting the diffusion of activated species, such as atomic oxygen, through to the surface (Ewenz Rocher et al 2019b). The surface pressure distribution directly influences the pressure differential across the porous medium and, the coolant mass flux distribution on its surface. The coolant concentration provides a deeper insight into the coolant path after exiting the porous wall and how it mixes with the hot external gas
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