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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。
Based on the theory of one-dimensional transient flow and the characteristic line method, the free gas cavity model is adopted, and the thermodynamic characteristics of the gas are taken into account to establish the mathematic model of the transition process of tailrace vent. Combined with the waterway layout and mechanical characteristics of the actual hydropower station, the overall mathematical model of the transition process of water diversion and power generation system is established to simulate the air intake and exhaust and partial gas-liquid two-phase flow in the transitional process. The results show that the air intake can effectively relieve the negative pressure in the tunnel, but the air is discharged with a large impact pressure, which is caused by the liquid column separated by the air, and the direct water hammer phenomenon occurs. When the vent area is larger, the impact pressure decreases with the increase of the area; when the vent area is smaller, the impact pressure increases with the increase of the area. According to its characteristics, the optimization scheme of the vent structure is proposed, that is, the orifice is fully opened at the time of intake, and only part of the vent is exhausted during the venting. When the vent area accounts for about 10% of the intake area, the pressure oscillation is well controlled .