In-situ 3D shape measurement system for a high-temperature object in a plasma wind tunnel via DMD-projection laser structured light and adaptive speckle filtering

Abstract The evaluation of an object’s 3D shape change during ablation in wind tunnel testing is critical for the optimization of the thermal protection system. However, strong thermal radiation and a harsh environment cause challenges to the traditional measurement methods. A single camera digital micro-mirror device (DMD) projector-structured laser light system is proposed for in-situ 3D shape measurement in a wind tunnel test. A customized DMD combined with a laser source is devised for projecting concentrated full-field high-power structured light stripes. To filter laser speckle noise in projected chessboard images for model calibration, an auto-window Kuwahara adaptive filter is put forward. The 3D shape of a blunt-head cylinder was in-situ measured in a plasma wind tunnel which reached a maximum temperature of 1950 °C. The diameter reconstruction error was within 0.85% (0.17/20.03 mm). With projected laser light and multi-step filters, the ablation process of the front face of a dome-top cylinder at 1950 °C was clearly observed at a long working distance over 1.5 m.