On Sediment Mass Flux Directionality Induced by Yawed Permeable Vanes under Near-Critical Mobility Conditions

Abstract

Experiments were conducted in open channel flows under near-critical mobility conditions to quantify local evolution of the sediment bed induced by emergent and submerged rectangular vertical porous walls in yawed conditions. The goal was to design minimally invasive hydraulic structures, or vanes, redirecting sediment mass flux to be coupled with intake pipes in dam bypass systems for sustainable sediment redistribution. Theoretical scaling for the maximum scour depth derived from the phenomenological theory of turbulence was extended to our specific emergent vane geometry under varying structure porosity, angle, and size. Most of our attention was devoted to quantifying the asymmetry of the induced bathymetric effects and developing an appropriate metric to identify the most effective vane configuration to steer sedimentation along a desired direction. The orientation angle was shown to significantly affect the geometry and volume of the scour and deposit, the spanwise shift of the deposit volume, and the velocity profiles in the wake, for both emergent and submerged vane configurations. The optimal streamwise and spanwise spacings in yawed, submerged, porous vane arrays were determined based on the spatial evolution of the wake flow, ensuring minimal sheltering effects and maximal lateral directionality of the sediment deposit. We here provide supporting evidence that wind and marine hydrokinetic turbine wake models can be extended to the case of porous planar structures to capture the key physical mechanisms governing sediment deposits.