Optical Flow Based Background Oriented Schlieren for Compressible Flows
B. O. Cakir (1,2), S. Lavagnoli (1), B.H. Saracoglu (1), C. Fureby (2)
(1) Dept. of Turbomachinery and Propulsion, von Karman Institute for Fluid Dynamics, Belgium
(2) Dept. of Energy Sciences, Lund University, Sweden
Optical flow provides an opportunity to e levate the resolution and s ensitivity of deflection se nsing in background oriented schlieren (BOS). Despite extensive relevant literature within the field of computer v ision, with regards to BOS, there is a lack of proper quantification of its abilities and l imitations. Thus, this study performs a comparative assessment characterizing accuracy and resolution limits in different flow field scenarios utilizing background patterns generated with speckle and wavelet noise distributions. Accordingly, a synthetic assessment over direct numerical simulations of a buoyancy driven turbulence is performed with variations introduced in the background patterns and operational parameters of optical flow where a c lear s uperiority o f a ccuracy a nd r esolvable r ange o f density
gradient amplitudes over cross-correlation is demonstrated. Moreover, an experimental assessment of supersonic flow features over multiple models is conducted to characterize the influence of experimental considerations related to the application of optical flow in BOS and its comparative performance against the block-matching counterpart.