Abstract
In open-channel flows, anisotropic turbulence is observed due to the existence of free surface. Open-channel flow has its own peculiar coherent structures and turbulence characteristics. In actual flooded rivers, the kolk-boil vortex is often observed on the water-surface and generated behind discontinuous boundary such as dunes and steps. It is important to examine the interaction between non-uniformities by unsteadiness effect and streamwise variation of bed shape. In the present study, the turbulent structures in unsteady open-channel flow over dunes were measured by means of fiber-optic LDA system. The mean-flow structures such as time variation of free-surface profile, bed shear stress and the turbulence statistics were discussed by comparing with backward-facing step flows. As the results, such mean properties can be explained by the effects of unsteadiness and spatial acceleration/deceleration which is caused by the shape of dune bed.
