Time-resolved optical flow of supersonic bevelled nozzles

Time-resolved Schlieren photography-based image velocimetry using optical flow techniques (SIVOF) was applied to supersonic jet flows issued from a 30° bevelled nozzle. A modified Z-type Schlieren system and a high-speed camera was used to obtain the Schlieren images, before they were post-processed using an in-house optical flow code. Convective velocities are recovered at significantly high resolutions, where the corresponding vorticity maps are observed to offer reasonably accurate identification and velocimetry of supersonic jet shear layer structures. Results are subsequently compared to and showcased against particle image velocimetry (PIV) measurements of the same supersonic bevelled jet. Behaviour of the vortical structures, shear layer growth rate, shock wave location and potential core length obtained from SIVOF agrees well with historical findings and previous studies conducted with the same nozzle design and nozzle pressure ratio (NPR) value. Lastly, the present study also highlights both the potentials and limitations of SIVOF in supersonic flow studies