Free Surface Effect on the Hydrodynamics of an Underwater Vehicle Hullform, the Darpa Suboff

This paper presents the numerical study on the hydrodynamic coefficients of the submarine hull form “DARPA SUBOFF” when deeply submerged and near the free surface when travelling straight ahead and at a range of drift angles. The Computational Fluid Dynamics (CFD)-based numerical model was validated with experimental data existing in the public domain for the SUBOFF, travelling over a range of drift angles when deeply submerged at a constant speed and in a straight line near the free surface over a range of speeds. The free surface effect on the hydrodynamic behaviour of the SUBOFF was then investigated throughout a range of speeds, drift angles and submergence depths. Results show that the effects of the free surface diminish rapidly with submergence and the near free surface hydrodynamic behaviour of the SUBOFF is highly Froude number dependent.