Large Eddy Simulation of Unidirectional and Wave Flows through Vegetation

Massively parallel large eddy simulation (LES) experiments were conducted to study the flow fields developed by unidirectional flow over submerged vegetation and wave flow-through emergent vegetation. For the submerged vegetation, vertical profiles of mean and turbulent horizontal and vertical velocities were found to be in good agreement with laboratory experiments. Canopy-averaged bulk drag coefficient calculated from the depth-integrated forces on the cylinders compares well with empirical measurements. For the emergent vegetation, wave-induced drag forces were calculated, and the inertia and pressure-drag coefficients were compared with laboratory experiments, which were found to be in good agreement. Vertical variation of forces and moments about the stem base are presented and compared with a single stem case under a variety of wave conditions and Keulegan-Carpenter (KC) numbers. It is seen that at low KC numbers the effect of the inertia force is significant. The vertical variation of the velocity field near the free surface, within two to three diameters from the cylinder center, was found to be considerably influenced by the free surface flux between the wave trough and the crest, over a time period, which creates a predominant recirculation zone behind the cylinder in the direction of wave propagation.