Simulation study on the hydrodynamic resistance and stability of a disk-shaped autonomous underwater helicopter

The hydrodynamic performance during multidirectional motions of a disk-shaped autonomous underwater helicopter, which are being developed recently, are investigated by means of computational fluid dynamics. High mesh quantity is essential to capture the realistic behavior during the horizontal motion. With the saucer-shaped basic geometry, pulsation of the drag force components against and normal to the moving direction is observed during the horizontal motion, which becomes more obvious with increasing velocity, while the motion is hydrodynamically more stable during the vertical movement with a relatively stable zero lateral force. At both moving directions, when the effect of thrusters are considered, the water flux induced by propellers disturbs the flow field, which enhances drag force fluctuation and moving instability. It is concluded that a high-performance controlling system is required to realize a stable and straight motion, or the dishing shape of the vessel needs to be optimized in order to improve the hydrodynamic stability.