Variable Transpiration Cooling: A New Solution for the Thermal Management of Hypersonic Vehicles

The overall aerodynamic performance of every flying vehicle is strongly dependent on near-wall effects. In hypersonic flows, the viscous effects near the wall have an even greater importance from the standpoint of thermal loads (i.e., heat flux and temperature distributions) and aerodynamic performance (i.e. L/D). Based on these considerations, it is important to understand the physics that characterize the boundary layer and its interaction with the vehicle\u27s surface to simulate its behavior for different surface parameters such as the type of material, surface manufacturing, surface coating, wall geometry, mass exchanges, etc. The work presented in this paper is focused on the mass exchanges at the surface, and investigates the cooling effectiveness of variable fluid injection into the hypersonic laminar boundary layer on a flat plate. A reduced order model that captures the relevant physics has been developed and implemented in a code that solves the Navier-Stokes equations written for stationary, no-reacting hypersonic boundary layer neglecting the radiative thermal exchange. The code uses a coupled solution of Self-Similar Method (SSM) and Difference-Differential Method (DDM) for a flat plate in the case of Pr=1 and Le=1. The variable transpiration is obtained choosing selected distributions for the coolant (air) velocity at the wall. The analysis of the minimization of the wall heat flux and of the coolant-s mass flow rate is performed. The comparison between the computationally inexpensive reduced order code and the CFD code GASP shows similar qualitative and quantitative results on the heat fluxes and shear stresses prediction