Expansion Tunnel Testing of the Electron Transpiration Cooling Effect

Electron Transpiration Cooling (ETC) has been proposed as a mechanism to augment heat rejection from hot components of hypersonic vehicles. While numerical simulations demonstrate the great potential of ETC, the experimental data that exist is limited and yet to validate results fully. Numerical simulations have shown that ETC provides significant cooling addition to thermal radiation, thus potentially enabling more aerodynamically efficient designs with sharper leading edges. A question that arises from the numerical simulations which must be answered by experimental testing is how to most appropriately model the ETC effects in the presence of hypersonic flow. This paper investigates suitable flow conditions for testing the ETC effect in the X2 Expansion Tube at the University of Queensland by collecting experimental data and developing a numerical model to predict measured currents. Different experimental measurement methodologies are analysed to assess their ability to show the effectiveness of the process. A wedge model was used to measure the current absorbed from the flow, to characterise the baseline measured current ahead of future ETC tests. A total of 17 experimental shots were completed while varying the flow conditions and bias voltages. A numerical predictor model was optimised from the results of each flow condition to account for variation between experiments in the flow speed and the initial biasing voltage. Results from the 6 km/s condition agree well with the modelling, however the 9km/s condition exhibits significant errors due to high variability in measured results. Further data is required to improve the modelling and enable the use of the 9 km/s condition. Future ETC tests will be completed using the selected 6 km/s flow condition and newly developed predictor model presented in this study.