TRPIV experimental study of coherent structures and their burst events in the boundary layer on JBC

Abstract

Turbulent drag on the hull surface is one of the main sources of drag during the navigation of a ship, which is significantly influenced by the boundary layer's coherent structures. To investigate the evolution and energy transport of the coherent structures, this study applied time-resolved particle image velocimetry (TRPIV) to realise the fine measurement of the flow field at different upstream and downstream positions on the surface of the Japanese bulk carrier (JBC). Finite-time Lyapunov exponent (FTLE), proper orthogonal decomposition (POD) and quadrant analysis were used to conduct a detailed analysis of the coherent structures and their evolution. The results show that the skin friction drag is notably affected by the coherent structures at the turbulent boundary layer of the JBC hull surface and their burst events. In addition, the turbulent energy that enhances the skin friction drag mainly comes from the outward-inward transport in the turbulent boundary layer, and the intensity of fluctuation velocity contained within the burst events also obviously affects the skin friction drag. The results of this study can provide physical evidence for the optimisation design of similar hull configurations, the optimisation design of unmanned underwater vehicle configuration, and the planning of drag reduction strategy.