通气系统对竖井式溢洪道水力特性影响研究

Influence of ventilation system on hydraulic characteristics of shaft spillway

跌流式竖井垂向落差大,通常在环形溢流堰与竖井段衔接处设置突扩形成脱壁流来降低水流急剧加速后对竖井壁带来的空蚀破坏风险,部分工程在突扩处设置有通气系统,但这种通气设置对于竖井溢洪道整体水力特性的影响尚未明确,针对易县抽水蓄能电站竖井溢洪道工程开展了物理模型试验。试验结果表明:随着堰上水头的增加,环形溢流堰水流流态从自由堰流向受阻堰流转换,最终变为压力孔口出流,且相较于不通气条件,通气条件下的流态转捩点提前;两种条件下泄流流量均呈现先增大后稳定的趋势,高水头时通气条件下泄流能力略低于不通气条件;同时研究发现H/H_(d)<0.88时,通气管的存在对竖井各水力特性的影响不大,但当H/H_(d)>0.88后,通气管的存在能够为竖井溢洪道提供更为充分的通气条件,有助于避免竖井管流现象的出现,且能够提高竖井溢洪道的消能率。研究成果可为跌流式竖井溢洪道的设计和优化提供参考。

The vertical drop of a drop-type shaft is large.The common practice is to set a sudden expansion at the junction of the annular overflow weir and the shaft section to form a detached flow and to reduce the risk of cavitation damage to the shaft wall after the rapid acceleration of the water flow.Some projects are set with ventilation systems at the sudden expansion,but the influence of this ventilation facility on the overall hydraulic characteristics of the shaft spillway is not clear.In this paper,a physical model was constructed based on the shaft spillway project of Yixian Pumped Storage Power Station.The test results showed that with the increase of the water head on the weir,the flow pattern of the annular overflow weir changed from the free weir flow to the blocked weir flow and finally to the pressure orifice outflow,and the flow pattern transition point under the ventilation condition was earlier than that under the non-ventilation condition.Under the two conditions,the discharge flow increased first and then stabilized,and the discharge capacity under the ventilation condition was slightly lower than that under the non-ventilation condition.At the same time,it was found that the existence of the vent pipe had little effect on the hydraulic characteristics of the shaft when H/H_(d)was less than 0.88,but when H/H_(d)was greater than 0.88,the existence of the vent pipe could provide more sufficient ventilation conditions for the shaft spillway,which is helpful to avoiding the occurrence of the shaft pipe flow phenomenon,and can improve the energy dissipation rate of the shaft spillway.