Rotational Temperature Imaging of a Leading-Edge Separation in Hypervelocity Flow

This paper presents a rotational temperature map of a leading-edge separation in a low-density hypersonic flow, obtained using imaged fluorescence of nitric oxide (NO). A flow condition with a total specific enthalpy of 3.8 MJ/kg, and for which the continuum assumption should hold, is generated using the T-ADFA free-piston shock tunnel. A leading-edge separated flow, known as the 'tick' model configuration and first suggested by Chapman et al. [1] for the study of laminar flow separation, is placed in this facility's test section to produce the leading-edge separation. This model geometry is chosen for the study because it produces a near zero-thickness boundary layer prior to separation. The planar laser-induced fluorescence (PLIF) thermometry technique was chosen to generate a spatially resolved rotational temperature map using multi-line fluorescence images [2]. This technique involves making multiple fluorescence measurements using different rotational lines across the gamma(0, 0) vibrational band of NO and fitting the signals to a Boltzmann plot. Using five isolated transitions, the measured freestream temperature of 155 +/- 7 K was in good agreement with a one-dimensional nonequilibrium inviscid nozzle code calculation of 156 +/- 8 K. The recirculating region was found to have a peak temperature of 2000 +/- 500 K across the imaged flowfield and the wake neck formed at the flow reattachment exhibited a cooling effect to an almost uniform temperature of 450 +/- 70 K.