Flow past a plate in the vicinity of a free surface

Abstract

Two-dimensional transient simulations are performed to investigate characteristics of flow past a plate normal to a stream. Free surface effects on the flow dynamics are the primary focus of this study. Varying plate depths are simulated to examine the variation of force coefficients and vortex shedding patterns. The k–ω Shear Stress Transport (k–ω SST) turbulence model and Volume of fluid (VOF) multiphase model are employed to predict characteristics of free surface flow. Flow past the plates is simulated at distances of 0.75m, 0.06m, 0.05m, 0.045m, and 0.03m below the free surface with corresponding local Froude numbers (Fr) of 0.18, 0.65, 0.71, 0.75, and 0.92. As the plate gets closer to the surface the drag coefficient decreases from 3.86 (Fr=0.18) to 2.18 (Fr=0.92) and the Strouhal number increases from 0.125 (Fr=0.18) to 0.355 (Fr=0.92). A jet-like flow formed from the surface is observed on top of the plate. Vortices from the top surface of the plate dissipate into smaller eddies due to the free surface presence, resulting in asymmetric vortex shedding downstream. Flows presented here are beneficial for designing and optimizing systems that harvest energy from marine currents.