Experimental study on water entry of circular cylinders with inclined angles

Abstract

A series of experimental studies have been carried out on water entry of three-dimensional circular cylinders for low Froude numbers. In our previous paper (Wei and Hu J Mar Sci Technol, 1:1–13, 2014), the results on horizontal circular cylinders have been reported, describing several typical three-dimensional water entry phenomena and discussing the effect of length-to-diameter ratios. In this paper, the results on inclined circular cylinders are presented. The emphasis of the study is paid on the effect of inclined angles. The effects of density ratio and length-to-diameter ratio are also considered. Translational and rotational motions of the cylinder are obtained from the image analysis of the video records by a high-speed digital camera. The lift force, drag force and torque on the cylinder are then estimated using the cylinder motions. Both quantitative and qualitative analyses are carried out on the experimental results. The major observations of this study are: (1) the cylinder with lower inclined angle experiences larger maximum drag force; (2) due to initial impact, the cylinder moves along a curved trajectory in water as a result of spin-induced lift force; (3) the inclined angle also makes the surface of cylinder relatively more hydrophilic; (4) when the cavity collapses, a sudden change of the trajectories and forces appears due to the free surface impinging on the cylinder.