A simplified photogrammetry procedure for quantitative on- and off-surface flow topology studies over 3D surfaces: application to a Gaussian bump geometry

A novel photogrammetry procedure is proposed for projecting 3D surface oil flow visualizations from 2D images over an arbitrary computer-aided design (CAD) model of a 3D surface. The technique yields a 3D view of the oil flow pattern on the model surface from different view angles and allows rendering it along with off-surface particle image velocimetry (PIV) flow field measurements. The technique is based on a recently developed simplified photogrammetry procedure proposed by Gluzman (Exp Fluids 63:118, 2022), which is modified to account for the full, large flow field over the 3D surface. The procedure requires only two reference markers on the given surface geometry CAD model, a small checkerboard placed on a flat surface near the 3D geometry, and a single camera that should capture at least three images after the experiment from any view angle in order to calibrate the projection. The proposed procedure allows removing the elaborate steps typically required in photogrammetry while retaining the same measurement accuracy. In particular, we demonstrate the application of the technique to study turbulent smooth-body flow separation over a Gaussian bump geometry in Gray (Part I-Exp Investig, 2023). Our photogrammetric procedure allows us to obtain a 3D view from different angles of the surface oil flow pattern warped over the CAD model geometry and coupled with stereo PIV plane flow field cuts, which provides important insights into the character of the flow separation.