A DES-based study of the flow around the self-propelled DARPA Suboff working in deep immersion and beneath the free-surface

Abstract

A series of numerical studies on an underwater vehicle performances, aimed at enhancing the accuracy of CFD application solutions is presented. The appended DARPA (Defense Advanced Research Projects Agency) Suboff is considered for which the unsteady RANS solutions are computed with the finite volume ISIS-CFD solver. Closure to turbulence is achieved either with the k−ω shear stress transport (SST) or with the hybrid detached eddy simulation (DES) SST turbulence models. The computed hull resistance is compared to the experimental data to validate the numerical approach. For the grid convergence test, computations are performed on four grids. Four different time steps are considered for the time convergence study. Solutions for the E1619 propeller working in open water are presented and discussed. Propeller open water curves are obtained for a range of advance coefficients covering high to moderate low loads, and results are compared with available experimental data. A V&V study is performed as well. Self-propulsion computations for the hull fitted with sail, rudders and the E1619 propeller are conducted and the resulting performances are presented and discussed. Finally, the near free-surface operation is considered by making use of a volume of fluid (VOF) approach. Three immersions are proposed and the solutions are compared with the unbounded flow results to emphasize the loss in the propulsion performance. The final remarks concludes that the main contribution of the work is the benefit in quality of using adaptive mesh refinement along with the hybrid SST-DES instead of using the faster but less accurate URANS SST methods or more the expensive LES-based methods.