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merits (i) they have no wall function approximations, (ii) they could compute low turbulence levels such as in the viscous sub-layer and (iii) they could account for the effect of damped turbulence. The low-Re models used in the present study are namely the models of Abe Launder-Sharma (k-ε LS), and Yang-Shih (k-ε YS). It has been found that the k-ε AKN low-Re model consistently provided superior performance in predicting the flow characteristics around underwater vehicle hull forms.

ABSTRACT:The aim of the current investigation is an assessment of the influence of free surface effects on hydrodynamic coefficients of an axisymmetric underwater body using Reynolds averaged Navier-Stokes (RANS) solver. This paper mainly focuses on the capabilities of turbulence models (two high-Re models, k- Re-Normalised Group (RNG) and k- Realizable and one low-Re model, k- Abe-Kondoh-Nagano (AKN) together with volume of fluid (VOF) method for hydrodynamic investigation of an axisymmetric underwater body (Afterbody1) near the free surface. The current numerical investigations were carried out to simulate measured hydrodynamic coefficients for several experimental parameters, including velocity variations from 0.4 m/s (Reynolds number Re v =2.12 10 5 ) to 1.4 m/s (Reynolds number Re v =7.4210 5 ), depth of submergence from 0.75D to 4.0D, and angle of attack 0 to 15 on a vertical plane for a model scale of 1:2. Numerical simulations were conducted at a grid density of 0.46 million cells based on grid independence study using a commercial flow solver, Fluent. Free surface effects on hydrodynamic coefficients (drag, lift and pitching moment) are studied from the calculated hydrodynamic forces and moments. Validation of numerical results is done by comparing with measured values. The present investigation found that the k- Realizable model together with VOF method consistently provided superior performance in predicting the free surface wave effects on hydrodynamic coefficients for Afterbody1 model. This study is expected to aid the selection of apposite RANS model for simulation of hydrodynamic forces over underwater bodies near the free surface.

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