Large eddy simulations of multiphase flows past a finite plate near a free surface

Abstract

Simulations have been conducted to quantify the effects of aspect ratio on the lift and drag coefficient for a finite plate near a free surface. Large eddy simulations using a VOF multiphase model were conducted for a plate length to height aspect ratio of 2.5, 5 and 10 for a Reynolds number of 50,000 and a Froude number of 1.3. Eulerian and Lagrangian coherent structures were employed to characterize the turbulent flow fields. As the aspect ratio increases, the mean drag coefficient decreases from 1.88 to 1.73. This is due to an increase in vortex activity caused by separation of the free shear layer at L/D of 5 and 10. Both the upstream and downstream region are affected by the hairpin-like vortices generated from the bursting of the free shear layer. With increasing plate length, Karman vortex shedding from the face near the free surface is suppressed, and the influence of tip vortices on the near wake flow is reduced. The aspect ratio has a strong influence on the free surface shape and dynamics because surface deflections increase with L/D. Free surface flows studied here provide valuable insight into designing off-shore structures, platforms, hydraulic and marine-current energy harvesting devices.