Relaxation effects in hypervelocity flow: selected contributions from the T5 Lab

Experimental access to flows in the total enthalpy range from 5 to 20 MJ/kg was greatly increased by Stalker's [1] introduction of the free-piston shock tunnel in the 1960's. Since then, experiments conducted in the later T series of these (T3 in Canberra, T4 in Queensland, T5 at Caltech) and the larger machines (HEG in Göttingen, HIEST in Japan) have changed the landscape of gasdynamics in this range enormously. Specifically, a number of previously unknown phenomena, some showing dramatic effects, were discovered by such experiments. The scope of this paper is much too constraining to do justice to the whole body of contributions of these research groups. Accordingly I will restrict it to a selection from those more familiar to me and that have come from the T5 laboratory. Much of the work in the total enthalpy range of the free-piston shock tunnels is concerned with the main enemy of this regime: heat flux.