The impacts of a groyne field on secondary flow phenomena in a high curvature bend

摘要: Groyne fields can be used to protect river banks against sediment erosion in regions of high curvature. While the low flow velocity within the embayments protects the outer bank, the main channel mean velocity is increased. Little is known about how groynes affect the structure and strength of the streamwise and cross-stream flow in sharp channels and their impact on erosion. This Large Eddy Simulation (LES) study compares flow without and with submerged groynes (channel depth/groyne height= 1.8) in a sharp 135 bend for initial scour conditions. Both simulations show that besides the main channel recirculation cell, strongly coherent streamwise oriented vortices (SOVs) form close to the inner bank. The LES results quantify the streamwise variation of the cross-stream circulation induced by the main eddies in the cross flow. Results show the groynes significantly increase friction velocity over part of the inner bank close to the SOVs. The larger potential for inner bank erosion should be considered in groyne design for sharp channels with banks close to vertical.