Preliminary Experimental Investigation of Air Radiation in Superorbital Expanding Flow

Radiative heating dominates forebody thermal loads on re-entry capsules travelling at superorbital speeds and has also recently been identified as a major component in afterbody heating. Although subjected to less severe heating, the afterbody heat shield is typically designed with a larger structural safety factor, limited by the fidelity of computational models used for the rapid flow expansion. To improve the understanding of afterbody flows, an experimental campaign was launched to interrogate the radiation from a rapidly expanding flow of 11.8 km/s air in the X2 expansion tunnel at the University of Queensland. Spectral measurements of the flow were successfully recorded from the ultraviolet to the near infrared, and two-dimensional images of atomic oxygen emission were also taken. The latter agreed well, in trend, with numerical simulations of the flow.