Investigation of visible to near-infrared high-speed cameras for thermography in hypersonic testing

This work investigates the implementation of visible to near-infrared high-speed thermography for the measurement of heat flux over blunt-body test models in an expansion tunnel. Recent works have seen success implementing mid-wave infrared thermography in the X2 expansion tunnel at the University of Queensland in Earth and Mars entry flow conditions. In this work, the performance of three visible to near-infrared high-speed cameras (Phantom v2012, v611 and TMX7510 models) is investigated in the context of thermography and a calibration methodology is presented. Visible to near-infrared high-speed cameras offer several benefits over the infrared cameras used in previous works, primarily increased acquisition rates which are imperative for the short test times encountered in these facilities. Resistive heating of the test model allows surface temperatures to be measured at a rate of 1 MHz even in the presence of a radiating shock layer. This is achieved through the careful selection of the following: the test condition which provides the baseline level of flow radiation, the operating wavelength region which can be chosen to avoid most of the remaining flow radiation, and the model pre-heating temperature which is chosen to increase the ratio between surface grey body radiation and the flow radiation. These radiation management strategies can allow the measurement of heat flux in low to medium enthalpy hypersonic ground test experiments in Earth's re-entry conditions and ice giant entry conditions within the visible and near-infrared regions of the spectrum.