Photogrammetry for accurate model deformation measurement in a supersonic wind tunnel

Abstract

The interest in adaptive devices for high-speed applications leads to the need for an accurate and reliable technique to obtain model deformation measurements during experiments. Point-tracking photogrammetry has been applied to supersonic wind tunnel testing, using four Phantom high-speed cameras placed on either side of the working section, where coded targets were applied to the surface of interest. Calibration experiments on a solid plate beneath a M = 1.4 normal shock and a M = 2 oblique shock allowed the quantification of the sources of optical distortion, namely the wind tunnel glass windows and aerodynamic effects (the lower pressure in the working section and the interaction between shock waves and the boundary layer). A correction matrix was applied to account for the optical distortion due to the glass, and the root-mean-square error due to aerodynamic effects ( < 0.03 mm) is believed to be negligible for applications with significant displacements (of the order of 1 mm). The application of photogrammetry to a flexible shock control bump has shown that the bump shape can be detected accurately, while disclosing some complex 3D effects that could not have been revealed by spanwise-averaged techniques such as schlieren photography.

Off-design performance of 2D adaptive shock control bumps

“…photogrammetry is employed to obtain accurate model deformation data during the experiments. As described in [15] and [16], four Phantom high-speed cameras are placed around the working section, and 80 coded targets, made of white vinyl, are attached to the flexible plate to facilitate the generation of the 3D model using the commercial photogrammetry software photoModeler by EOS Motion [17]. For this setup, the RMS error was calculated to be 30 µm [16], which can be considered negligible for the experiments presented in this paper.…”

Shadow-Imaging-Based Triangulation Approach for Tool Deflection Measurement

“…Photogrammetry is a particularly suitable approach for measuring the 3D positions of multiple points with reflector targets [11]. Industrial applications include deformation measurements, i.e., displacement field measurements of the object's surface, of a model in a wind tunnel [12] or of a wind turbine blade in static and fatigue tests [13]; alignment of row parts before machining [14]; or the tracking of robot end-effectors [15]. Although tracking robot end-effectors is a similar application to tool tip measurement, transferring the measurement principle is neither practical, due to the use of reflector targets that are too large to be placed close to the tool tip, nor does it reach a sufficient dynamic range [6].…”