动水关闭的平面事故闸门体型优化试验研究

在已建水利水电工程中,利用自重、配重与水柱压力动水关闭的平面事故闸门,时常会出现无法完全闭门的现象,严重威胁水电站的正常运行及上下游安全。为探究其产生原因并找到有效的解决措施,该文针对进水口平面事故闸门出现的类似问题,采取水力学模型试验的方法,通过门体水柱压力试验以及不同体型闸门的闭门持住力对比,并结合闸门水动力荷载特性进行分析,明确事故闸门在动水中无法完全关闭是由工程摩擦系数(0.209)过大所致;基于伯努利原理,从增加水柱压力的角度出发,采取在平面闸门迎流面底部增设前缘板块,并对其下表面端部进行加厚处理的优化方案,在模型试验中,达到了增大闸门闭门持住力、促进闸门顺利关闭的效果,表明了该方案对解决已建工程平面事故闸门在动水关闭过程中无法下落问题的有效性。

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.