An experimental sensitivity comparison of the schlieren and background-oriented schlieren techniques applied to hypersonic flow

An experimental study was performed to evaluate the spatial resolution, sensitivity and dynamic range of schlieren and background-oriented schlieren (BOS) applied to hypersonic flows with multiple density gradients. For a single Mach number, shock profile extracts for three values of freestream density are compared. Three processing metrics are proposed for BOS to optimise the sharpness of captured shocks and minimise processing blur are presented. The BOS results have a lower spatial resolution and sharpness than the schlieren images, but captured the model flow field features that were resolved by schlieren. A higher dynamic range was afforded for BOS due to the user-determined synthetic knife edge cut-off.