Numerical investigation of a fleet of towed AUVs

This paper investigates the influence on the fleet of the drag of multiple towed prolate spheroids to determine the hydrodynamic effect of the viscous interaction between hulls and to study the influence of the configuration׳s shape of multiple hulls in the vee and echelon formations. A series of CFD RANS-SST simulations has been performed at the Reynolds Number 3.2×106 by a commercial code ANSYS CFX 12.1. Mesh convergence is tested and then validated with experimental and empirical results. The drag of each spheroid is compared against the benchmark drag of a single hull. The results show that the spacing between two hulls determines the individual drag and combined drag. The dominant spacing has been classified into seven zones based on the drag characteristic of twin towed models. Regions are characterised to parallel, echelon, no gain, push, drafting, low interaction, and no interaction. Both the multi-vehicle vee and echelon configurations show limited influence against that of the entire fleet׳s energy budget. For an individual spheroid where a lower propulsion cost is required, then the use of three/four in vee or echelon formation should be considered. Based on this numerical information, operators can determine the optimal fleet configuration based on energy considerations.