尾水隧洞通气孔进排气瞬态过程研究

基于一维瞬变流理论和特征线法,采用自由气体空穴模型,并考虑气体的热力学特性,建立了尾水通气孔的过渡过程数学模型。结合该类水电站实际工程的水道布置及机械特性,建立引水发电系统过渡过程整体数学模型,模拟过渡过程工况下通气孔进排气及局部气液两相流。结果表明:通气孔进气可以有效缓解隧洞中的负压,但空气排出时伴随较大的撞击压力,其来源于被空气分隔的液柱重新弥合,发生直接水锤现象。通气孔面积较大时,撞击压力随着面积的增加而减小;通气孔面积较小时,撞击压力随着面积的增加而增加。根据其特性,提出通气孔结构优化方案,即进气时孔口全部打开,排气时只有部分孔口排气,当排气面积占进气面积10%左右时,压力振荡得到较好的控制。

Investigation on hydraulic transients in tailrace tunnel with air inlet and release from the vent

Based on the one-dimensional hydraulic transients and the method of characteristics (MOC), the mathematical model of the vent in the tail race tunnel is established by using the Discrete Free-Gas Cavity Model (DGCM),and the thermodynamic properties of the gas is taking into account as well. A corresponding numerical model has been developed using the data of a real hydropower station, and the phenomenon of air inlettwo phase flow-air releases is investigated during transient process. The results show that air inlet can effectively relieve the negative pressure in the tunnel, but air releases can lead to a large impact pressure, which comes from the water column rejoin after the separation by the air, resulting in the direct water hammer. When the area of the vent is large,the impact pressure decreases with the increase of the area, when the area of the vent is small, the impact pressure increases with the increase of the area. According to its characteristics, the structure of a new type of vent is presented, i.e., the vent is fully open when the air flows in, and the vent is partly open when the air flows out. When the air releases area is about 10% of the air inlet area,the pressure oscillation is small.