Study on hydrodynamic characteristics of the disk-shaped autonomous underwater helicopter over sea-beds

In this study, the hydrodynamic characteristics of the Autonomous Underwater Helicopter surging near the seabed are studied by numerical simulation and experiment. The influence from the cruising velocity, altitudes as well as the inclination angle of the seabed are considered. For the condition of flat seabed, the simulation shows that the seafloor mainly affects the flow field at the bottom and rear part of the AUH, which changes the pressure resistance, and consequently affects the total resistance. In addition, bulges at the top and bottom of the AUH are the cause of the abnormal lift force. For the condition of sloping seabed, at the same surging velocity and cruising height, the resistance of AUH is more than twice of the one over flat seabed, and the irregular eddy current intensity at the tail of AUH increases with the increasing slope angle. The hydrodynamic performance from simulation agrees with the findings from the water-channel experiment with the adoption of a scaled model of the vessel. It is further discovered that hydrodynamic characteristics of AUH change more obviously with the angle of attack when it is more close to the seabed. Therefore, the hydrodynamic performance of AUH near the sloping seabed can be improved by adjusting the angle of attack.