Background oriented schlieren technique with fast Fourier demodulation for measuring large density-gradient fields of fluids

In order to measure the large density-gradient fields of fluids such as underwater shock waves, we employed a fast Fourier demodulation called Fast Checkerboard Demodulation (FCD) method in Background Oriented Schlieren (BOS) technique. BOS is simple image-based measurement technique that detects apparent displacement (local distortion) background image caused by density gradient fluid front background. The cross-correlation particle velocimetry (PIV) method, which commonly for detecting displacement, uses random-dot background, whereas FCD periodic pattern (e.g., checkerboard pattern, lattice grid (grid scale)) detect phase change space. this study, measured proportional fluid, an wave using and PIV. results showed can up 2.5 times larger than PIV measure. Furthermore, systematically investigated limit FCD-BOS changing several parameters patterns, size. Also, explored related space understand limitations. It worth noting with scale) accurately custom-made indicating be setup commercially available (inexpensive) pattern.