Improvement of hydrodynamic performance of the disk-shaped autonomous underwater helicopter by local shape modification

Abstract

The hydrodynamic performance and the way to reduce the drag and increase the motion stability for a newly developed hovering autonomous underwater vehicle, a disk-shaped AUH (autonomous underwater helicopter), are investigated by computational fluid dynamics as well as pool and water-channel validation experiments. The hydrodynamic property is improved through local modification at the rear part of the original hull geometry (HG1), which results in a fore-aft asymmetric geometry (HG3). From the numerical simulation, it is found that with proper extension and sharpening at the rear part, separation of the boundary layer is delayed and the secondary flow area is effectively suppressed, which results in a remarkable reduction of the hydrodynamic drag as well as the drag and side force fluctuation. For the basic AUH hull, the temporal average drag of HG3 (65.3 N) is 26.5% lower than that of HG1 (88.9 N) at u=2m/s. The HG3 geometry also shows good stability against disturbance by the aquatic cabin attached at the central bottom, as well as propellers imbedded in the hull in a realistic working condition compared to the original geometry.