Flow regimes of submerged rectangular sharp-crested weirs in sand bed channel

摘要

Laboratory experiments were conducted out to investigate the regimes of submerged flows over the sharp-crested weirs in sand bed Channel. These kinds of flows were classified as five states such as (I) impinging jet, (II) bed surface flow, (III) surface jump, (IV) surface wave, and (V) surface jet based on the depicted vector plots of the regimes. By increasing the submergence ratio, the impinging jet was developed as a downward jet which was impinged from the weir crest to the downstream. By continue the increasing, flow regime was developed as a bed-surface flow which is supposed that the impinging jet is turned as flow near the bed position instead of having a direct impact with the bed. Additionally, increasing constancy of the submergence ratio causes that the bed-surface regime turned to the surface jump which is accompanied by a hydraulic jump at the water surface. Subcritical condition at downstream of the weir which is provided by raising the tailwater due to constant flow discharge causes that the surface wave regime has vanished at the water surface of the downstream of the weir and some oscillating waves were transferred to downstream. Finally, by considering the maximum range of submergence ratio, the flow regime was changed to the surface jet which was accompanied by a big clockwise vortex at the lower water elevation. The present study classifies these flow regimes based on the velocity components (u, v, w). This approach was chosen by the authors to show the different classification between visual inspection and investigating the velocity direction by ADV. Then, an empirical equation was proposed to show the boundaries of the presented regimes. Also, a dynamic restriction was proposed based on experimental and literate data as a non-eroded status that is due to a submerge ratio, the scour hole is not provided at downstream of sharp-crested weir.