Sensitivity and resolution response of optical flow-based background-oriented schlieren to speckle patterns

The degraded resolution and sensitivity characteristics of background-oriented schlieren (BOS) can be recovered by utilizing an optical flow (OF)-based image processing scheme. However, the background patterns conventionally employed in BOS setups suit the needs of the cross-correlation approach, whereas OF is based on a completely different mathematical background. Thus, in order to characterize the resolution and sensitivity response of OF-based BOS to the background generation configurations, a parametric study is performed. First, a synthetic assessment based on an analytical solution of a one-dimensional shock tube problem is conducted. Then, a numerical assessment utilizing direct numerical simulation data of density-driven turbulence is performed. Finally, the applicability of the documented conclusions in realistic scenarios is tested through an experimental assessment over a plume of a swirling heated jet.