Winglet effect on hydrodynamic performance and trajectory of a blended-wing-body underwater glider

Winglet has been widely used in aviation industries to improve the performance of aircraft. However, according to the authors' knowledge, the effect of winglet on underwater gliders has not been investigated in detail. This paper aims to investigate the impact of winglet on hydrodynamic performance and gliding trajectory of a blended-wing-body underwater glider (BWBUG). The hydrodynamic performance of the BWBUG without winglet (BWBUG-I) is firstly calculated. Then the hydrodynamic performance of BWBUG with winglet (BWBUG-II) is analyzed and compared. To estimate the influence of winglet on gliding trajectory, a dynamic model is established by considering the buoyancy and pitch regulating system. From the CFD results, the lift force acting on the glider is increased by the winglet, while the drag force remains at the same level. The lift-to-drag ratio is thereby improved. By comparing trajectories, the average gliding ratio for BWBUG-II is 5.10, 2.2% higher than 4.99 for BWBUG-I. With the winglet, the extreme attack angle is reduced from 7.2° to 6.1° when switching from rising to diving. The steady gliding speed is improved by 6.3%, and the squat depth is reduced by 11% under particular condition.