Experimental investigations on air entrainment by means of impinging jets

The phenomenon of air entrainment as a result of an impinging water jet was experimentally studied by means of videometry and image processing methods. A series of experiments at different conditions was performed and evaluated. Each experiment consisted of a 10s recorded sequence with a frequency of 200Hz. Jet lengths varied between 0.01m and 0.2m and jet exit velocities ranged between 0.8m/s and 2.5m/s. Image processing algorithms were applied to extract information about jet penetration depth, width of the bubble plume and bubble size distribution. Therefore, images were subdued to background subtraction, binarization and averaging. Bubble sizes were estimated from single images by subsequent background subtraction, cell segmentation, bubble detection and bubble size calculation by means of a Hough-transform based algorithm. It was found that the bubble sizes were in accordance to the data present in the literature. The penetration depth of the plume was compared to an empirical formula presented by Bin in the literature. It was established that in addition to the impact velocity, the amount of entrained gas has a significant effect on the penetration depth.