Dynamics and morphology of single ellipsoidal bubbles in liquids

• An original postprocessing method of raw images of ellipsoidal bubbles is developed.
• The alignment of the mass center velocity vector and the minor axis of an ellipsoidal bubble is experimentally shown.
• The interface curvature radii at the front and rear of a bubble are evaluated experimentally and a correlation is established.
• A pulsation is identified in the vertical motion of a zigzagging bubble.

A data postprocessing method for an imaging technique based on shadowgraphy is presented in this paper. It enables a precise analysis of the dynamics of a bubble rising in a liquid. The morphology of the bubble is also precisely analyzed by determining an appropriate threshold for the binarization of the images. Experiments with single ellipsoidal bubbles rising in various water–glycerol mixtures, with an oscillatory trajectory and without interface wobbling, are analyzed. It is rigorously shown that the minor axis and the mass center velocity vector of a bubble are aligned in the cases of a zigzag and a helical motion of the bubble. The interface curvature radii at the front and at the rear of a bubble are determined and, in the case of a zigzag motion of the bubble, a correlation to calculate their ratio is proposed. In the vertical motion of the mass center of a bubble, a pulsation at twice the frequency of its horizontal motion is identified in the case of a zigzag motion of the bubble. In the case of a helical motion of a bubble, such a pulsation cannot be identified in the vertical motion of the mass center of the bubble.