Effects of transpiration fluid properties on Boundary Layer Instability Mechanisms*

The management of intense thermal loads encountered by hypersonic vehicles operating in the atmosphere

can be effectively alleviated by utilizing transpiration cooling, which involves the injection of cold fluids at

the vehicle’s surface. However, injection can substantially impact flow stability and potentially

induce a premature transition to turbulence. The primary objective of this study is to comprehensively

understand the mechanisms responsible for the destabilization of the flow for different injection fluids. To

assess the influence of injection gas properties on the stability of high-enthalpy boundary layer flows, air

and CO2 injections are being considered. Both fluids are introduced at the same mass flux, resulting in

a comparable reduction in heat flux. Disturbance energy budget analysis is used to explain the relevant physical mechanisms. Furthermore, Bi-Orthogonal Decomposition is used to differentiate the different contributions from eigenmode spectrum.