Transpiration cooling in hypersonic turbulent boundary layer

Abstract

The design of new-generation reliable and efficient hypersonic flight vehicles requires analysis and validation of an effective technique to suppress the intense heat loads that generating on the vehicle surface. The purpose of the present contribution is to study the characteristics of a hypersonic turbulent flow over a porous-injecting wall, representative of a transpiration cooling system, and to analyse the pore-size effect on the coolant performance. Direct numerical simulations (DNS) are carried out for a Mach 5 flow over a flat plate. A porous injection model has been designed which mimics coolant injection from a bed of equally-spaced circular pores. Rapid transition to turbulence is triggered by high-amplitude disturbances imposed on the wall upstream of the porous region. Results show that a turbulent wedge-shaped flow structure generates just downstream of the injection region, which produces a reduction of the surface coolant concentration. The pore size influences flow features and coolant concentration in the laminar region, however has a marginal effect within the turbulent region, where the wall-cooling performance depends predominantly on the fluid dynamics of the turbulent flow. The present work sheds light on the effects of turbulence and pore size on transpiration-cooling characteristics in hypersonic flow, still poorly understood and not in-detail explored in the literature. Results indicate that the turbulent-wedge flow features must be deeper investigated with focus on the coolant redistribution, and that a parametric-study-informed tailored calibration of different porous injection parameters is vital for controlling the flow features to optimise the cooling performance.