Multi-Dimensional Numerical Free Surface VOF Modeling With Moonpool Experiments

Abstract

The homogeneous multiphase incompressible flow past a moonpool was investigated to determine the shape of vortex, flow field and pressure distributions. In this approach, a homogeneous flow model together with the VOF method for interface capturing is used to compute the entire flow field within the moonpool. The turbulence is represented via fully homogeneous buoyant model with air and water as continuous fluids. Numerical results are verified by conducting towing tank experiments. Simulation ship moonpool applications are verification of capabilities in ANSYS CFX multi-physics code by two and three dimensional circular and square shaped moonpool subjected to flow in a channel. The numerical results indicate that cavity location with a unit factor of 1.667(L/L1), where ‘L’ is length of cavity and ‘L1’ is the distance from inflow edge; was proved to be appropriate for such cavities to have optimum performance related to moonpool hydrodynamics. Distance ‘L2’ had a negligible effect on cavity. Free surface height ‘H’ inside the cavity was maintained at 0.4 m both in numerical calculations then in experiments. Numerical and experimental comparison of results reveals that due to multiphase modeling; results diverge from actual value near phase coupling. Shape factor like internal curvature, has a great influence on vortex shape and hydrodynamic forces inside the moonpool. By analyzing these numerical results a better understanding is established for VOF models and moonpool piston phenomenon. Square shaped moonpool results and numerical results agree very well till half of the moonpool depth from free surface height. These results can be very well used for the basis of designing complex shaped moonpool having free surface. The agreement with the experimental data is within the accuracy of other simulations. Further studies and the development of Best Practice Procedures are required as a next step to reduce/avoid numerical and set-up errors and establish CFD as an industrial tool.