Control of undular weir flow by changing of weir geometry

• We investigated the undular flow characteristics above the broad-crested weir.
• Effect of weir inflow geometry on the undular flow has been studied.
• When the weir upstream slope reduced, the wave relative height decreased.
• Reducing the upstream face slope increases the wave relative length.
• The curvature of upstream corner of the weir decreased the wave relative height.

Undular flow above the broad-crested weirs is an open channel flow phenomenon which occurs under certain hydraulic conditions. The flow surface on the weir transforms to sinusoidal waves and the number of waves may vary from one to over 10. Hence weir cannot be utilized to measure the flow discharge due to the formation of surface undulations above its crest. Propagated waves can be disturbed remarkably to the channel downstream. In this study, effects of upstream face slope of rectangular broad-crested weirs on the undular weir flow were investigated. The results obtained indicated when the weir upstream slope reduced from standard angle 90° to 40°, the relative wave height decreased up to 78% and the relative wave length increased up to 55%. The experimental results showed that wave was not generated above the weir with 21° upstream face. Furthermore, effects of the radius of curvature of weir upstream corner on the undular wave characteristics were studied. This study established that curvature and slope has similar effects on the wave elimination.