Variable Transpiration Cooling Effectiveness in Laminar and Turbulent Flows for Hypersonic Vehicles

Abstract

Reusable thermal-protection systems with active cooling, such as transpiration, are among the promising technologies for thermal management of hypersonic vehicles designed as practical, long-range transportation systems. This paper numerically investigates the effectiveness and efficiency of a variable-velocity transpiration technology for fully laminar and fully turbulent hypersonic flows over a two-dimensional blunt leading-edge geometry. For both flow types, variable transpiration based on a sawtooth velocity distribution is compared to a uniform-velocity transpiration approach. An equal amount of coolant has been imposed to compare the cooling effectiveness between two strategies. The results numerically demonstrate the significant reduction in stagnation-point heating and coolant mass savings achievable with the variable-transpiration strategy, which is observed both in laminar and turbulent flows. The transpiration cooling efficiency is shown to be higher in laminar flow compared to turbulent flow downstream of the leading edge (ramp region). In such regions, for turbulent flows, the amount of total coolant must be increased by a factor of 2 to match the cooling efficiency in laminar flows. The thermal response of a porous thermal-protection-system material is investigated in laminar and turbulent flows with variable transpiration to gain important insight about the matrix and coolant behavior in response to external flow.