Flow visualization of supersonic projectiles with color gradient background oriented schlieren

A modified background-oriented schlieren (BOS) technique is presented that uses a rear-projected, color gradient to improve flow visualization in high-speed experiments. Previous work has shown that color gradients can provide unique advantages versus traditional random dot backgrounds in steady-state scenarios. Here, the technique is demonstrated under dynamic, unsteady events. Traditional BOS relies on "speckle" patterns which require refractive disturbances that appear larger than individual-colored regions. Color gradients are not reliant on background pattern size and is instead limited by the resolution of the camera. Here flicker free cinema lights project a smooth color gradient behind the test section, enabling real-time adjustment of pattern and intensity. Traditional BOS relies on comparing images before and after shocks through one of a variety of image processing algorithms to produce quantitative measurements of test-section refraction. Color gradients remove the need for these processes instead allowing for direct image subtraction for quantitative results. This minimizes computing requirements and processing time. Tests are being conducted first with laboratory based air shocks, then with supersonic projectiles.