Analysis of the unsteady wake of a full bottomed ship in shallow water

Abstract

The paper is devoted to the analysis of the unsteady hydrodynamic processes

taking place in the ship wake under shallow water conditions. The motivation of the research is the determination of the reasons for the rise of strong vibration in the stern of inland cruise ships in the waterways with considerable depth restriction.

As a research tool the hybrid URANS/LES approach of Kornev et al. [1] is selected in order to capture the influence of nonstationary vortical structures on the velocity oscillations in the propeller plane. As it will be shown, URANS method cannot reproduce these flow features.

The flow is studied in a single-phase and in a two-phase formulation. Influence of the free surface, depth Froude number and depth to draft ratio on the wake is analyzed. The adverse pressure gradient in the stern region causes massive separations of the boundary layer. On account of the separations the velocity oscillations in the wake are turned out to be strongly dependent on the under keel clearance.

On the other hand, it is shown, that at high F rH the wave pattern can significantly

influence the viscous wake and cause the suppression of the velocity oscillations due to the decrease of the water level. Possible effect of the wake unsteadiness on the propeller

performance in such circumstances is discussed.