ABSTRACT
Local scour downstream of a weir is common problem, which can result in serious damage to the weir itself and instability of the downstream channel. Local scour downstream of the weir can be attributed to the force exerted on the bed by highly 3D flows generated by the weir. Specifically, such flows are characterized by the separated shear layer and unsteady large-scale coherent structures. This study presented the results of large eddy simulation (LES) of the flow over a submerged weir to investigate the characteristics of the turbulent flows downstream of the weir. LES was applied to the flat bed (FB) case and the deformed bed (DB) case with a scour hole. Time-averaged velocity was compared with measured data for validating computations. Coherent structures near the bed were examined using uw quadrant analysis. For the FB case, the splats occur frequently with strong sweep event near the reattachment point. On the contrary, the splats rarely occur and relatively weak sweep events remain near the reattachment point for the DB case.
