On the physical mechanisms for the numerical modelling of flows around air lubricated ships

Air lubrication techniques are very promising in reducing ship drag. It has been demonstrated that air cavity applications can realise propulsive power reduction percentages of 10-20% due to the reduction of the frictional resistance [1, 2]. However, a complete understanding of the two-phase flow physics involved with air cavity flows is still missing. Multiphase CFD methods can help to get a better understanding of these physics. The largest challenge in predicting the air cavity characteristics lies in the correct modelling of their closure (reattachment) region [3, 4]. In this region the separated air-water flow transforms into a more dispersed flow. The transformation is partly caused by instabilities in the two-phase flow. This article aims to link the physical modelling of the relevant phenomena to their numerical modelling. The link to the numerical modelling is addressed with an emphasis on different RaNS and hybrid RaNS-LES turbulence models. The article is based on the available literature in the public domain and knowledge gained in research projects carried out at Delft University of Technology and Maritime Research Institute Netherlands (MARIN).