Gate Vibrations due to Unstable Flow Separation

The unsteady load and vibration behavior of vertical‐lift gates was investigated for different gate‐bottom geometries and disharge conditions in an open channel and at a conduit inlet. In all cases, vibrations occurred in specific ranges of a dimensionless velocity parameter whenever the flow fluctuated between complete separation and reattachment at the gate bottom. The excitation mechanism was attributed to the combined effect of shear‐layer instabilities and motion‐induced vortices shed at the leading edge of the gate bottom. Many puzzling features of in‐flow and cross‐flow vibration of gates with flow underneath can thus be clarified. In addition, it is shown that the slope of the mean lift curve acting on the gate bottom provides an effective means of predicting with reasonable accuracy the critical range of gate openings with respect to potential gate vibration. The prediction method is illustrated in a practical case.