Water entry of hollow cylinders with fronts of different fillet radii: A visualization study

Abstract

In the present study, we investigate the water entry of three hollow cylinders with fronts of different fillet radii of 0, 5, and 10 mm. Particular attention is given to the effect of fillet radius of front on cavity dynamics. To interpret the mechanism of cavity evolution, a high-speed photography system is employed to capture instantaneous impact phenomena and behaviors of the hollow cylinders. Unique characteristics of the internal jet and ring-rupture pinch-off of the cavity are described and discussed. The results show that both dynamic patterns and characteristic parameters of the cavities differ with the fillet radius of the front. For the flat-front hollow cylinder, a fully developed streamlined gas cavity is formed, and the expansion rate and size of the cavity are substantially greater than those associated with slanted fronts. The cavity trajectory remains nearly vertical, and the internal jet is the most extended. With increasing fillet radius of the front, underdeveloped cavities with relatively small size are produced and the collapse time of the cavity is shortened. Furthermore, the cavity trajectory is characterized by lateral deflections, and the maximum attainable height of the internal jet is reduced.