Structural optimization of emergency plate gate for closure in moving water

Abstract: In the actual hydraulic engineering projects which are already completed, the emergency plane gates should be closed in the moving water under the action of self-weight, additional weight and water column pressure. However, the problem that the emergency gate isn't completely closed in moving water is frequently occurred in engineering practice, which is a serious threat to the normal and safe operation of the hydropower station. In order to clarify the generation mechanism and investigate the effective solution for this engineering problem, the hydraulic model tests were carried out and the obtained experiment data were analyzed. Firstly, on the basis of hydraulic model experiment, we measured the water column pressure. Secondly, the holding forces of the emergency plane gates with different bottom shapes were compared and the characteristics of hydrodynamic excitations acting on the gate leaf and gate bottom were analyzed. The results showed that the beam grillage system of the gate was reasonably designed and the water column pressure was made full use of. The flow pattern under the gate was relatively stable and the flow excitation characteristic was reasonable, meaning that the currently adopted bottom shape was appropriate and the flow fluctuation pressure acting on the gate leaf and gate bottom was not the main cause of this engineering problem. Consequently, the analysis results indicated that the cause of the aforementioned engineering problem was that the friction coefficient (0.209) between the gate leaf and gate groove was seriously underestimated, and the substantially underestimated friction coefficient was verified by prototype test results. In order to make this emergency plane gate completely closed in moving water, an optimal scheme of gate shape was further presented by adding a steel guide plate on the bottom edge of upstream surface. The water above the steel guide plate could be approximately regarded as still water, while the water below the guide plate flew through the gate hole with a relatively high speed. Therefore, the downward pressure was induced by the flow velocity difference between the upper and lower surfaces of the guide plate according to the well-known Bernoulli Principle. Due to the increment of the downward force, the minimum opening ratio of the emergency plane gate that could be reached in the gate closing process was decreased. This indicated that the gate shape optimization scheme was effective, but not enough to make the plane gate completely closed in moving water. In order to ensure the complete closure of the emergency plane gate in moving water, the aforementioned optimization scheme was further improved by thickening the upstream lower surface of the added guide plate. This improvement led to the streamline separation under the lower surface of steel guide plate. According to the flow fluctuating pressure data measured by the pressure sensors installed on the lower surface of guide plate, the negative pressure was observed in most working conditions, which indicated the effectiveness of this improvement. By applying the emergency gate shape optimization and its improvement, the twice amplification effects of the downward force acting on the gate was generated, which would significantly facilitate the complete closure of emergency plane gate in moving water. According to the experimental results, the presented engineering optimization scheme and its improvement measure were very effective for this problem and the modified emergency plane gate could be completely closed in most working conditions.