Refurbishment and characterisation of the Oxford Low Density Hypersonic Wind Tunnel

In the study of atmospheric entry, one of the most challenging environments to model is the lower phase of the transition regime between free molecular and continuum behaviour. This regime, known as slip flow, occurs at Knudsen numbers between 0.001 and 0.1, i.e. when the mean free path of the gas around an object starts to become significant compared to said object’s physical dimensions. The Oxford Low Density Wind Tunnel is a continuous flow facility specifically designed to model this regime (at Mach numbers in the range 5 6 Ma 6 10) which has recently been re-commissioned with a range of new subsystems including upgraded instrumentation. This paper presents experimental flow characterisation measurements for two conditions, specifically Mach 5 flows at Kn = {0.0066˙ , 0.02}, performed using Pitot pressure and total temperature surveys. These results confirm the suitability of the wind tunnel for simulating hypersonic slip flow problems such as those associated with atmospheric entry calculations.