虹吸式出水管虹吸形成过程的壁面压力及脉动特性

Wall pressure and fluctuating characteristics of a siphon outlet pipe during siphoning formation process

通过物理模型试验测量虹吸式出水管在虹吸形成过程中典型断面的压力过程线,采用邻域平均法提取脉动压力数据,采用统计特征和短时傅里叶变换信号处理方法分析时均和脉动压力特征。结果表明:管壁时均压力沿水流方向先减小后增大,驼峰段的上壁面时均压力随着流量增大逐渐大于下壁面;虹吸形成过程中,压力脉动呈正偏态分布,均方差沿水流方向不断降低;压力脉动主要由水泵旋转和水气运动引起,频率在0~30 Hz之间,主频与水泵转频相近;相比虹吸稳定流阶段,水力驱气阶段存在的气囊压缩和释放过程使得压力脉动频率及幅值上升,接近泵站系统自振频率,容易产生结构振动,需要通过设计和运行的优化减少该阶段的持续时间。

The pressure process line at typical sections of a siphon outlet was measured by physical experiment. Pressure pulsation of the siphoning formation process was obtained by the neighborhood average method, and the statistical characteristics and short-time Fourier transform signal processing method were conducted to systematically analyze the universal change law for time-averaged pressure and pressure pulsation. The results show that the time-averaged pressure on the wall, along the flow direction, first decreases and then increases. The time-averaged pressure on the upper wall of the hump segment changes with the flow rate and is gradually greater than that of the lower wall. The pressure pulsation in the process of siphon formation has a positive skew distribution, and the quadratic mean deviation keeps decreasing along the direction of the flow. The pressure pulsation in the process of siphon formation is composed of the rotation of the pump and the movement of water-air, which has a frequency between 0 and 30 Hz, with the dominant frequency close to the rotation frequency. Compared to the entrainment stage and siphoning flow stage, a significant increase in pressure frequency and amplitude occurs in the purging stage, which is close to the natural frequency of pumping station, leading to structural vibration. Design and operation should be optimized to reduce the duration time of the purging stage.