The effect of hull form on the optimum L/D ratio for minimum resistance for submerged bodies

For minimum resistance, the optimum slenderness (L/D) ratio for an underwater vehicle hull based on a near optimal ‘teardrop’ hull shape is generally considered to be around six. However, in practice the optimal hull shape is rarely achieved, with most modern underwater vehicles such as submarines and autonomous underwater vehicles (AUV) having parallel mid-body sections. Thus, the optimum L/D ratio is different from that established on the basis of a teardrop shape.

This study involves the use of Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamic (CFD) simulations to quantify the resistance characteristics of three submarine hull shapes with different L/D ratios. The results were used to identify the optimum L/D ratio for minimum resistance for each of the hull forms. The hull forms include the DST generic conventional Joubert submarine geometry, the DARPA standard SUBOFF hull form, and the Teardrop shape that is optimal in terms of hydrodynamic resistance. The CFD simulations were validated against published measurements from captive model experiments. The results presented provide a comparison of the resistance for the shapes and the optimum values of L/D for each different shape are given.

The results are also used to establish an approximation technique which can be used to predict the resistance of a hull shape for different L/D ratios. The value of the approximation technique is at the concept stage of a submarine or underwater vehicle design, where it is necessary to have a prediction for the resistance prior to the commissioning of any model tests or CFD simulations, both of which are relatively expensive and time consuming.