Using VOF Slip Velocity to Improve Productivity of Planing Hull CFD Simulations

Use of Computational fluid dynamics (CFD) tools is becoming common practice in the analysis of high speed craft. These numerical tools are of great value, since they can provide high-fidelity insight into performance of various designs by modelling non-linear effects due to viscous forces and turbulence. However, CFD tools are often seen as computationally expensive and prohibitive in a design environment. One of the main issues that impacts the use of CFD tools is numerical ventilation, when air is artificially entrained beneath the hull while using the Volume of Fluid (VOF) scheme to model the free surface. To overcome this issue, traditionally, very fine grids are requested near the surface of the hull to resolve the flow. In this paper, it will be illustrated how the use of an algebraic VOF slip velocity, in conjunction with a tight overset model and adaptive mesh refinement prevent the issue of numerical ventilation while simultaneously using a more computationally efficient mesh that produces accurate results in calm water resistance calculations. A verification and validation process comparing the VOF slip velocity method against experimental data for a known hull was conducted. Computational cost and accuracy associated with VOF slip velocity is discussed. The methodology is then applied to a stepped hull and comparisons between towing tank experiments and simulation results are looked at.