On the Turbulence Modelling for an Air Cavity Interface
Author Rotte, G. and Kerkvliet, M. and Van Terwisga, T.J.C.
Title On the Turbulence Modelling for an Air Cavity Interface
Conference/Journal 20th Numerical Towing Tank Symposium (NuTTS), Wageningen, The Netherlands
Month October
Year 2017

Abstract
The use of air lubrication techniques can significantly reduce a ship’s fuel consumption. One of the most promising techniques applicable to ships is the external air cavity technique. An external cavity is created beneath the ship’s hull with the help of a cavitator, which is located directly upstream of an air injection point (figure 1a). The cavitator is extended in the span-wise direction and typically has a rectangular or triangular cross section. It is used to separate the mean water flow from the hull, thereby providing a stable air layer. Air cavity applications are claimed to lead to propulsive power reduction percentages of 10-20% by reducing the ship’s frictional drag. However, a complete understanding of the influence that the ship’s hull form has on the relevant twophase flow physics and thereby also on the length and stability of the air cavities is still lacking. This inability to predict the air cavity characteristics hampers the application of air cavity techniques in the shipping industry. Multiphase CFD methods can help us to gain a better understanding of the relevant physics.
This article aims to link the physical modelling of the relevant phenomena to their numerical modelling, with an emphasis on the modelling of the re-entrant jet mechanism with a RaNS turbulence model. The article is based on the available literature in the public domain and on knowledge gained from research projects carried out at Delft University of Technology and at the Maritime Research Institute Netherlands (MARIN).

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