Visible Light Refraction Effects on High-Speed Stereo Digital Image Correlation Measurement of a Thin Panel in Mach 2 Flow

This study utilized a Mach 2 wind tunnel, Research Cell 19 (RC-19), where the panel specimen became part of the test section top wall. Two stereo digital image correlation (3D-DIC) systems simultaneously acquired displacement measurements both with and without flow by filming the front and back sides of the panel. The two DIC results were then compared to note if any changes between the two measurements could be attributed to light refraction distortions. Various flow conditions were investigated including varying stagnation pressures and multiple shock angles to characterize and quantify potential distortions over a range of conditions. Previous work showed that the distortions were largely quasi-static in nature which had little or no bearing on vibration measurement however, static deflections caused by thermal gradients and less than ideal boundary conditions could be important for finite element model updating. Current results indicate that distortions at the shock wave foot were present in the DIC displacement results however, the level of distortion could be considered the same magnitude of typical sources of measurement noise and not significant.