Impact forces by a gravity current on a circular cylinder above the seabed

Abstract

Large-eddy simulations (LES) were conducted to determine the wave forces by a gravity current on a circular cylinder for various elevations above the seabed at a laboratory-scale Reynolds number Re=840 and a Reynolds number Re=23500. The performance of five LES models was evaluated by mesh-refinement study and comparing the simulation with the laboratory observation at the Re=840. We then selected the best-performed model for simulation of the wave impact at the higher Reynolds number of Re=23500. The simulations determine the wave deformation of the current and the transient development of the force for different elevations of the cylinder above the seabed and different ambient-water depths. At the high Reynolds number of Re=23500, the lift coefficients in the directions toward and away from the seabed were comparable in magnitude to, and in some instances exceeding, the drag coefficient in the direction of the current. The wave interaction had led to the drag and lift coefficients being much larger than the known coefficients for the steady flow of uniform density.