Visualization and thermometry in hypersonic wedge and leading-edge separated flows

Abstract

This paper presents preliminary nitric oxide planar laser-induced fluorescence (NO- PLIF) measurements of rotational temperature in hypersonic flow for a 30° wedge and a leading-edge separation (tick-mark shaped: 3) model. The experiments were conducted in the T-ADFA free-piston shock tunnel at two flow conditions with specific enthalpies of 3:1MJ=kg and 11:3MJ=kg. For the wedge, thermometry was done at the low-enthalpy condition to validate the performance of the PLIF system and image processing method. The freestream temperature and shock angle are both in good agreement with the predicted flow conditions, but the post-shock temperature is 300K lower than expected. Additionally, there is a 50% increase from the nominal freestream temperature as the flow travels towards the shock wave, which affects approximately 5mm upstream of the shock. Both the low post-shock and high freestream temperatures are linked to fluorescence bleed, where high fluorescence signal from one side of the shock increases signal on the other side, introducing an error in the calculated temperature. For the tick model, PLIF visualization was done at the low-enthalpy condition and PLIF thermometry was done at the high-enthalpy condition. Comparison between the tick images at the two conditions shows that the recirculation bubble size is larger and the wake neck further downstream for the low-enthalpy condition. At the high-enthalpy condition, the freestream temperature was 150K lower than the predicted value and the temperatures in the recirculation bubble and recompression region have uncertainties up to 60% of the local temperature caused by low signal-to-noise ratio.