Flow dynamics in the closure region of an internal ship air cavity

TL;DR

This study investigates the complex, turbulent flow dynamics within the closure region of an internal ship air cavity using advanced simulation techniques, revealing unsteady flow behavior and air-water mixing mechanisms.

Contribution

It provides detailed insights into the flow behavior and turbulence in the closure region, employing large-eddy simulation with interface capturing, which is novel for this application.

Findings

Flow in the closure region is highly unsteady and turbulent.

Pressure gradients cause flow separation and recirculation zones.

Linear theory predicts wave phase and length well, but underestimates amplitude.

Abstract

This work is dedicated to providing a detailed account of the flow dynamics in the closure region of an internal ship air cavity. A geometrically simple multiwave test cavity is considered, and a simulation of the flow is conducted using large-eddy simulation coupled with an algebraic Volume of Fluid interface capturing method. Results reveal that the flow in the closure region is highly unsteady and turbulent. The main cause of this is established to be the pressure gradient occurring due to the stagnation of the flow on the beach wall of the cavity. The pressure gradient leads to a steep incline in the mean location of the air-water interface, which, in turn, leads to the flow separating from it and forming a recirculation zone, in which air and water are mixed. The separated flow becomes turbulent, which further facilitates the mixing and entrainment of air. Swarms of air bubbles leak periodically. Upstream of the closure region, the phase and length of the wave are found to be well-predicted using existing approximations based on linear flow theory. However, for the corresponding prediction of the amplitude of the wave the agreement is worse, with the estimates under-predicting the simulation results.