Numerical Study on the Hydrodynamic Performance of the Darpa Suboff Submarine for Steady Translation

Abstract This study was built upon previous works conducted by the authors in a series of numerical studies on submarine hydrodynamics and is aimed at enhancing the accuracy of computational fluid dynamics (CFD) application processes, which estimate the hydrodynamic performance of underwater vehicles for steady translation conditions in the horizontal and vertical planes. In an earlier work, the computed straight-ahead resistance of a submarine agreed with those of experiments within a comparison error of 2%. However, a maximum comparison error of approximately 20% was obtained for sway force under a steady translation condition. The Defense Advanced Research Projects Agency (DARPA) Suboff submarine model was adopted as a benchmark, and the computational modeling was based on the Reynolds-averaged Navier–Stokes (RANS) turbulence model for steady simulations. The curvature correction approach was tested to improve the computation of circumferential flow around the cylindrical hull, in particular. The dominant maneuvering coefficients were calculated using the computed forces and moments as a function of the yaw and pitch angles along with simplified equations of motion by fitting a curve to the plots. The hydrodynamic forces and moments exerted on the stern plane were individually computed using a locally refined mesh around the tail section. It was confirmed that the curvature correction approach improved the computational accuracy for the steady translation conditions, and general trends were captured over the tested yaw and pitch angles. However, some data points had notable comparison errors. Some of the estimated maneuvering coefficients agreed well between the CFD simulation and the experiments, whereas others had considerable comparison errors. The individually computed forces and moments exerted on the stern plane that had attack angles were inconsistent with those obtained in experiments. Those comparison errors may have been amplified by the complexity of configuration and arisen from differences in the experiments, such as the presence of a free surface and supporting strut to mount the hull to a carriage, and, perhaps, the geometrical differences owing to machining accuracy. The investigation of flow field at the propeller plane revealed that the wake distributions inside the nozzle were significantly affected by the angled stern planes; the reduced velocity area was expanded and shifted. Furthermore, harmonic analysis of the wake fraction was conducted, and several primary nth harmonics were observed, which were associated with the struts and stern planes. This result suggests the risk of higher noise levels associated with the number of blades.