Numerical study of water depth effects on the hydrodynamic performance of a shallow-water seismic survey ship’s Z-drive ducted propeller

To meet the propulsion requirements of a novel shallow-water seismic survey ship, a Ka+19A Z-drive ducted propeller was designed based on ship model resistance tests using the propeller chart method. Numerical simulations of open water tests were conducted using Reynolds-Averaged Navier-Stokes (RANS) and transient Rigid Body Motion (RBM) methods, obtaining the open water performance curves. Compared to the original propeller test values, the results verified that the designed propeller could provide effective thrust for the shallow-water seismic survey ship, ensuring its smooth navigation. By varying water depth conditions, the effects of different water depths on the hydrodynamic performance of the Z-drive ducted propeller were investigated, and the influence of shallow-water effects on vortex structures and propeller wake velocity was explored. The results revealed that as the water depth H decreased from deep water to 5D, the influence on open water performance was minimal. However, as H decreased further from 5D to D, significant shallow-water effects emerged, characterized by increases in both the torque coefficient KQ and total thrust coefficient KT. Notably, the increase in KT was more pronounced than that of KQ, which resulted in an improvement in open water efficiency η0. Additionally, the vortex structures and wake velocity demonstrated that the bottom boundary exerted a minimal influence when H decreased from deep water to 2D, but its effect became pronounced when H=D. This study provided guidance for numerical simulation of ducted propellers in shallow-water environments and for propeller design and selection for shallow-water ships.