DRAG REDUCTION OF SUBMERGED MOVING BODIES USING STEPPED HEAD SHAPE

Friction drag force exerted on submerged moving bodies substantially increases by increasing the speed. Viscosity of water is much higher than that of the air or vapour. Therefore, if the submerged body is covered by vapour, there will be a large drag reduction. Vapour can be naturally produced due to cavitation. When a body moves in water with high speed, cavitation is inevitable, and it may extend all around the body. Extent of the cavity depends on the body head shape. Investigations were made to find head shapes with larger cavity and smaller pressure drag. Cylindrical stepped heads are studied in this work. It is tried to optimize the shape by changing the steps lengths. Numerical methods employed to predict the vapour bubble size and drag forces for different stepped heads. The results show that shorter steps produce larger cavities, and longer steps produce smaller pressure drags. The optimum step sizes are found between these two extremes