Discharge Coefficient and Head Loss under Sluice Gates with Small Opening

The water flow under a high-dam gate with a small opening has rarely been studied. The discharge coefficient and head loss under sluice gates are studied experimentally, with the relative gate opening less than 0.10, including the free and submerged flow. The semiempirical formula for the discharge coefficient is proposed, which is used to estimate the overflow capacity of the free and submerged flows with a relatively small gate opening. The equation of the bed friction head loss of the submerged flow in the boundary layer is derived by using boundary-layer theory. The local head loss and the head loss caused by the flow turbulence in the eddy area are estimated, respectively. The results show that for the free flow, the inflection point of the vertical contraction coefficient, discharge coefficient, and total-head-loss coefficient varying with the relative gate opening was 0.04. The head loss caused by the flow turbulence in the eddy area played a leading role in the total head loss for submerged flow. The results can provide a reference for the design and operation of high-dam deep-hole gates.