Image Processing For Bubble Image Velocimetry in Self-Aerated Flows

In this study, different preprocessing techniques have been applied in order to test if the accuracy of Bubble Image Velocimetry (BIV) calculations in self-aerated flows can be improved. For this purpose, high-speed movies with a resolution of 1920 × 1200 px and a frame rate of 730 Hz are captured on a stepped spillway model with a Phantom M120 camera supplied by LaVision. BIV results are obtained by application of the open-source Matlab® toolbox PIVlab and compared to intrusive data from a double-tip conductivity probe. Averaging velocity fields from 249 frame pairs help to obtain robust results. Therefore, BIV is carried out in a loop with preceding variation of image processing techniques. Results show some potential improvement for the same cross correlation algorithm and post-processing options. However, BIV results tend to underestimate flow velocities when compared to the conductivity probe data.