Large-scale simulation of ship bubbly wake during a maneuver in stratified flow

Abstract

We study the stratified bubbly wake of the research vessel Athena R/V during an overshoot maneuver using a polydisperse two-fluid model. The motions of ship, rudders and propellers are handled with a dynamic overset approach. The demands of the resolution of the flow and the small time step imposed by the rotating propellers make this problem very demanding and challenging. We discuss the dynamic response of the ship, focusing on trajectory, motions, forces and moments. Vortical structures and their effects on bubble and density transport are studied. Efforts are then focused on studying the bubbly flow and density distribution, and how vortices and flow field affect bubble entrainment, density and bubble transport, and size distribution. Results indicate that the void fraction and maximum depth in the wake increase during the maneuver, as do the disturbances to the stable stratification. Bubble entrainment during the maneuver increases in the transom stern but decreases around the hull, resulting in more bubbles in the wake. Due to transport of bubbles entrained around the hull into the inboard side of the turn, the resulting wake is also wider than in straight self-propulsion operation.