Shear layer behavior under a streamwise vibrating gate and its significance to gate vibration.

Abstract

A flow visualization study of the shear layer movement beneath a submerged, vertical, flat-bottomed gate model with underflow and which undergoes forced streamwise vibration of fixed amplitude and frequency is presented. Computer simulation based on the flow visualization photos, coupled with measured discharge flow velocities and hydrodynamic pressure distributions on the gate, permits the estimation of the fluctuating discharge coefficient and the phase lag between the fluctuating discharge and the gate motion. The motion of the downstream portion of the shear layer is shown to correlate Well with the observed discharge fluctuations. A mechanism of energy transfer for self-excited vibrations of vertical gates positioned above a horizontal bed is identified. The excitations due to the pressure distributions along the upstream and downstream faces of the gate are shown to be approximately equal.