Two-fluid modeling of bubbly flows around surface ships using a phenomenological subgrid air entrainment model

The quantitative prediction of bubbly flow around a maneuvering surface ship is critical in determining its hydrodynamic performance and its acoustic and optical signatures. It is a challenging multiscale problem that relies heavily on subgrid models of turbulence and air entrainment. In this manuscript we analyze this problem using a phenomenological air entrainment model that predicts the location and rate of air entrainment around a surface ship. This subgrid model was coupled with a two-fluid Reynolds averaged Navier Stokes (RaNS) bubbly flow model and used to evaluate the flow field around a naval surface ship in straight ahead and turning motions. For straight ahead motion the predicted void fraction distributions aft of the stern were compared with experiments at three different ship speeds and good agreement was found. The qualitative differences in the location of the air entrainment and the resulting bubbly flow between straight ahead and steady turning motions were discussed and compared with experimental observations at sea. To our knowledge this study presents the first quantitative numerical prediction of void fraction distributions around a full-scale surface ship, well matching the experimental measurements.

► Phenomenological subgrid model for the location and rate of air entrainment around surface ships.
► RaNS two-fluid model for the subsequent bubbly flow field.
► Air entrainment predicted at the masker, along the contact line, and in the transom wake.
► Greater rates of air entrainment and a more heterogeneous bubbly wake in a turning ship motion.
► First time quantitative numerical prediction of void fraction around full-scale surface ships.