Data on bubble entrainment and comminution are gathered in three experiments, involving the breakup of a disk of air trapped between two plates, and bubble cloud generation under a waterfall, and a plunging jet. In the second two cases, an automated acoustic system for characterizing the entrainment is employed. The data sets are compared with an existing theory for bubble fragmentation, in which a key parameter is the number of spatial dimensions associated with the insertion of randomly positioned planes which are used to divide up the bubble. While an appropriate best-fit theoretical curve can be obtained for the bubble population histograms generated by air disk comminution, waterfalls and plunging jets produce multimodal distributions which the theory cannot model. The differing roles of shape oscillations and surface waves in bubble fragmentation, and the issues involved with incorporating these into the model, are examined.
The use of electronic visual displays for background-oriented schlieren allows for the quick change of the reference images. In this study, we show that the quality of synthetic and background-oriented schlieren images can be improved by acquiring a set of images with different reference images and generating a median displacement field from it. To explore potential benefits, we studied different background changing strategies and their effect on the quality of the evaluation of the displacement field via artificial and experimental image distortions.
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