Visible Light Refraction Effects on High-Speed Stereo Digital Image Correlation Measurement of a Thin Panel in Mach 2 Fl
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S.I. : COMPUTER VISION AND SCANNING LASER VIBROMETRY METHODS
Visible Light Refraction Effects on High-Speed Stereo Digital Image Correlation Measurement of a Thin Panel in Mach 2 Flow Timothy J. Beberniss1 · David A. Ehrhardt2 Received: 8 April 2020 / Accepted: 18 October 2020 © This is a U.S. government work and not under copyright protection in the U.S. 2020
Abstract 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. Keywords Digital Image Correlation (DIC) · Shock wave · Refraction
Introduction High-speed digital image optical diagnostic techniques such as schlieren, fast reacting pressure sensitive paint (PSP), Shack-Hartman wavefront sensor, for flow quantification [1–4] and high-speed 3D-DIC for compliant panel vibration measurement [4, 5] have matured into invaluable tools for high-speed wind tunnel measurements. The noncontacting and full field nature of these methods are an attractive alternative to more traditional intrusive and/or discrete sensor location techniques. In the interest of studying the phenomena of high-speed fluid-thermalstructure interaction (FTSI), 3D-DIC has emerged as a powerful method for vibration measurement of a thin panel subjected to a high-speed flow environment [6–8]. This strength of 3D-DIC is due to the spatially complex, fullfield, wide-band random nature of flexible panels’ dynamic response in these environments. Timothy J. Beberniss
[email protected] 1
US Air Force Research Labs, 2790 D St. WPAFB, Dayton, OH 45433, USA
2
Ehrhardt Engineering LLC., Monticello, IL, USA
The measurement technique of DIC in general can be considered quite mature given the years of research by, for instance Sutton [9]. Over the past 10 years vibration measurement utilizing 3D-DIC techniques has become a well established alternative to more traditional methods such as discrete, contacting accelerometers. [10– 12]. Despite the many clear benefits of 3D-DIC for fullfield non-conta
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