Experimental study on the time-averaged flow velocity distribution around a ship in restricted waters

When a ship navigates in restricted waters, the complex interaction between the moving hull and the confined water body generates a distinctive flow structure. The spatial distribution of the time-averaged flow velocity near the hull directly affects the ship’s maneuverability and stability, and plays a critical role in ensuring operational safety. In this study, high-resolution Particle Image Velocimetry (PIV) technology was employed to conduct open-channel turbulence tests using a scaled ship model in a restricted water environment. The distribution characteristics of time-averaged velocity around the hull were examined, focusing on the effects of varying cross-sectional coefficients and inflow conditions. The influence of these two key factors on the longitudinal and vertical components of the time-averaged velocity was analyzed. Results show that the maximum longitudinal velocity U in restricted waters appears beneath the ship. Influenced by the descending flow at the bow and the ascending backflow behind the stern, the vertical velocity V peaks near the bow and downstream of the stern, with the most significant velocity changes occurring near the bow. The dimensionless longitudinal time-averaged velocity beneath the hull exhibits an asymmetric "⊃"-shaped distribution along the vertical axis. The vertical flow velocity initially increases and then decreases from the hull bottom to the channel bed, approximating an "S"-shaped pattern within the stern vortex region. The longitudinal time-averaged velocity decreases with an increasing cross-sectional coefficient, with its maximum value reaching approximately 1.35 times the average cross-sectional velocity. However, the position of the velocity peak remains largely unaffected. As the inflow velocity rises, the longitudinal time-averaged velocity increases accordingly, and the dimensionless profile reveals distinct zoning: the high-velocity zone beneath and in front of the hull expands, the low-velocity zone near the bow contracts, and the stern backflow zone enlarges. Nonetheless, variations in inflow velocity do not significantly alter the location of maximum flow velocity. These findings provide a scientific basis for the design and maintenance of restricted waterways and the safe navigation of vessels.