Wave Systems in an Internal Ship Air Cavity and Their Effect on Air Leakage: A Numerical Investigation

Paper in proceeding, 2021

Ship air lubrication using hull cavities is a promising technology for achieving significant friction drag reduction for large vessels. In this study, high-fidelity simulations, based on a methodology coupling Large-Eddy Simulation with Volume of Fluid interface capturing, are used to compute the flow in a model scale cavity. The primary goal is to capture the secondary, divergent waves appearing inside the cavity due to the presence of sidewalls. Flow at three Froude numbers (Fr) is considered, in order to obtain different interference patterns between the primary and secondary wave systems. This also allows investigating whether the air leakage mechanism depends on Fr. The divergent wave systems are successfully captured in the simulations. At Fr=1 they do not appear to influence the air leakage. However, for the two lower Froude numbers (0.76 and 0.81), a tendency towards more intensive leakage near the sidewalls is observed, and it is speculated to be caused by the divergent waves. The leakage mechanism itself does not appear to change with Fr in spite of the associated difference in the phase of the primary wave as it approaches the cavity closure.