The Effect of Adaptive Sampling on Fluorescence Velocimetry Measurements in High-Speed Flows

Abstract

An adaptive sampling technique has been assessed experimentally for determining the peak location of Doppler-shifted lineshapes for fluorescence velocimetry measurements in high-speed flows. Acquired data from three regions of an imaged leading-edge separation in hypersonic flow were fitted with Gaussian profiles and the Doppler-shift compared with that of a uniform sampling technique. Lineshape peak locations from both methods were similar, although significant scatter in fluorescence intensity values were found to reduce the effectiveness of adaptive sampling, which led to an almost uniformly spaced distribution of sample frequencies. Additional longitudinal laser modes were identified as the cause of the intensity scatter, which originated from an intra-cavity etalon not performing at factory specifications. The experimental implementation of the adaptive sampling technique using the current setup rendered its performance to be approximately the same as a uniformly spaced sampling approach.