Transpiration-Cooling Heat Transfer Experiments in Laminar and Turbulent Hypersonic Flows

Abstract

The design of a transpiration-cooled system requires detailed local heat transfer information on and in the vicinity of the porous injector; however, limited spatially resolved experimental studies exist, particularly in hypersonic flows. In this work, experiments were conducted in the University of Oxford’s high-density tunnel at Mach 6.1 in both laminar and turbulent regimes. Spatially resolved two-dimensional surface heat transfer measurements were acquired by imaging directly on and downstream of two microporous transpiration-cooled injectors (METAPOR® CE170 and zirconia) using high-speed infrared thermography. Whereas injection in the laminar regime results in a steady, monotonic reduction in heat transfer from the start of the injector, a flatter profile is present for the turbulent cases where turbulent mixing inhibits surface heat transfer reduction. It was found that a modification to existing relations from film theory successfully correlates the streamwise heat transfer distribution on the injector for different blowing rates of nitrogen and helium. A key result is that helium performs much better than reported in previous experiments. Finally, the downstream thermal effectiveness is characterized for turbulent flows. A collapse of the thermal effectiveness is achieved and a modified analytical correlation proposed.