Rattanasiri, Pareecha, Wilson, P.A. and Phillips, A.B.
Numerical investigation of the influence of propeller to the interference drag of twin prolate spheroids at various longitudinal offsets and transverse separations.
In, USYS'12: 4th International Conference on Underwater System Technology , Southampton, GB,
The purpose of this paper is to provide guidance for operators on suitable spacing for multiple vehicle missions. This paper investigates the combined drag of a pair of propelled prolate spheroids and compared to the towed models for the Reynolds Number of 3.2×106. The model has a length-diameter ratio of 6:1. A series of configuration of a pair of spheroids is simulated at various longitudinal offsets and transverse separations. Three-dimensional simulations are performed using a commercial Reynolds Averaged Navier Stokes (RANS) Computational Fluid Dynamics code ANSYS CFX 12.1 with the SST turbulence closure model. In each case, the fluid domain has a mesh size of approximately nine million cells including inflated prism layers to capture the boundary layer. Mesh convergence is tested and then validated with wind tunnel test results. The drag of each spheroid is compared against the benchmark drag of a single hull. The three-dimensional cylinder is modelled to simulate the thrust distribution of propeller. The drag of the propelled model is compared against the single bare hull model. The results show that the transverse separations and longitudinal offsets determine the interaction drag between both hulls. The increasing of separation results in lower interference drag. The decreasing of offset results in higher drag reduction. By implementing the body force propeller, the combined drag and drag of the follower is interfered by the accelerated flow. Based on the numerical information, operators can determine the optimal configurations in transvers separation and longitudinal offset based on energy considerations.
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