充压伸缩式水封破坏机理及处理措施

充压伸缩式水封在水利枢纽工程高水头泄水孔中应用日益广泛,但由于多种原因,弧形闸门可能会出现漏水,甚至出现水封及连接件破坏现象。某实际工程在第一汛期底水封压板上的M20不锈钢螺栓大部分旋出冲走;增大压板螺栓直径(由M20改为M27)、提高螺栓等级(由A2-70改为10.9级)后,第二汛期螺栓又出现断裂。以该工程为例,采用物理模型试验方法,并结合相关计算,研究了弧形工作闸门底水封附近的水力特性。分析结果表明水封系统破坏机理的主要原因是高速水流引起的负压、空蚀及流激振动诱发的水封系统共振。通过试验方案优化研究,提出了在门槽斜坡跌坎下游布置消力坎的工程措施。试验结果表明:出口段水流条件得到很大改善,水封处负压消失,水流空化数增大,消能减蚀效果明显。此外,还提出将水封压板与座板的弹性连接结构改为刚性连接结构,使得水封系统的固有频率远离水流脉动压力优势频率分布区,避免水封系统共振。研究结果可为类似的弧形工作闸门水封设计和故障处理提供参考。

Failure Mechanism of Pressurized Expansive Water Seal and Countermeasures

Pressurized expansive water seal is widely applied to weep holes of high head in water conservancy project. Due to many reasons, radial gate may suffer from leakage or even failure of the water seal and adapting pieces. Taking an actual project for example, most M20 stainless steel bolts on the bottom water clamping plate rotated out and were washed away in the first flood season after operation; in the second flood season, the bolts still fractured even after enlargement of the diameter of bolts (from M20 to M27) and improvement of bolts grade (from A2-70 to 10.9). In view of this, we investigated the hydraulic characteristics in the vicinity of the bottom water seal of the working radial gate via physical model test. Results unveiled that negative pressure and cavitation induced by high-velocity flow and resonance generated by flow-excited vibration are major causes of the failure of water seal system. Furthermore, through scheme optimization, we proposed an engineering countermeasure, which is to arrange baffle sill in the downstream reach near the slope of the gate slot. Test results demonstrated that flow condition in the exit segment has improved remarkably, negative pressure of water seal vanished, and flow cavitation number increased, implying evident energy dissipation and corrosion reduction effects. In addition, we recommend rigid connection instead of elastic connection between the clamping plate and the base plate in order to avoid resonance of the water seal system by keeping the natural frequency of the water seal system far from the dominant area of frequency distribution of fluctuating pressure. The research findings offer reference for the design and fault treatment of water seal system of radial gate.