Experimental study on water entry of inclined circular cylinders with horizontal velocities

Abstract

The complex impact cavities and motion behaviours of water entry by a multi-degree-of-freedom motion cylinder are investigated experimentally for different initial horizontal velocities and inclined angles. The cylinder is released above the free surface with controlled component velocities and inclined angles by a newly designed mechanism. A high-speed photography technique is employed to reveal the unique cavity flow phenomena that vary with horizontal velocity and inclined angle and to record the corresponding position of the cylinder in water. The cavity dynamics, including the initial jet, open cavity, surface seal, cavity break, break jet, side cavity and pinch-off, are investigated for different initial impact conditions. Moreover, the effects of horizontal velocity, inclined angle and angle of attack on the motion characteristics are studied. The experimental results demonstrate a special cavity flow phenomenon, a suction airchannel, that is due to the closure of the splash dome prior to the growth of the cavity volume. For cases of violent cavity break, a water wedge is formed as the break jet penetrates into the fore end cavity. The hydrodynamics of impact force, pressure drop and spin-induced lift acting on the descending cylinder cause obvious curvature in the trajectory. In particular, when the absolute value of the angle of attack is greater than 22°, a circuitous phenomenon is found, and the inclined angle decreases rapidly as the cylinder descends.