LES OF VEGETATED OPEN CHANNEL FLOWS BASED ON THE DRAG COEFFICIENT DISTRIBUTION THAT TAKES INTO ACCOUNT THE APPROACHING VELOCITY TO EACH CANOPY ELEMENT

Abstract

The drag-force model has a bottleneck in choosing the model drag coefficient C_D. An appropriate C_D profile is estimated by a numerical simulation where fluid motions around each canopy element are fully resolved in a minimal unit of the target flow. While Yokojima and Kawahara (J. JSCE B1 71(4) 2015) computed C_D (C_D;global) based on the bulk-mean velocity as the velocity scale , the present study obtains a C_D profile (C_D;local) taking into account the approaching velocity to each element. Application to vegetated open-channel flows reveals that neighter C_D;local nor C_D;global gives satisfactory results. Including the unsteady effects and/or reformulating the model expression might be required for better performance.