Experimental study of a vertical plunging jet by means of a volumetric shadowgraph technique

A vertical plunging jet has been investigated experimentally by means of an innovative volumetric shadowgraphy technique. A space carving algorithm has been used for the measurement of the size and concentration of the air bubbles, to follow the air bubbles path inside the investigated volume, providing both spatial and temporal evolution of the same. Furthermore, the air bubble tracking has been performed by means of an algorithm based on the Lucas-Kanade optical flow algorithm. Results highlighted a distribution of the air bubbles that follows the free jet spread inside the investigated volume with a dependence of speed and size from the action exerted by the vertical jet. The volumetric shadowgraph technique has proven effective in characterizing air bubbles, also in presence of relevant void fraction.