Correlating film thickness with coarse-particle trajectories in a soap film tunnel

Here we focus on correlating coarse-particle trajectories with interferometric measurements in a soap film tunnel. The problem of flow past a cylinder at moderate Reynolds numbers is known to have a near constant Strouhal number. We compare the particle trajectories with estimates of relative film thickness, vortex shape, and speed approximated from interferometric data. Monochromatic light produced by low-pressure sodium lamps makes visible alternating light and dark vortex rings, which indicate a variation in film thickness through interferometry. Fluorescent polyethylene particles with diameters O (10-100) microns are seeded into the soap film and illuminated by an ultraviolet light, and their behavior is recorded by a high-speed camera. The resulting image sequences are processed using MATLAB to plot coarse-particle trajectories and observe flow behavior in the wake of the cylinder. Preliminary results indicate an ability to correlate wake behavior observed using particle-laden flow with relative film thickness derived from interferometric data.