尾水管内气液两相流动测量

Measurement of Gas-Liquid Two-Phase Flow in Draft Tube

当水轮机在部分负荷工况下运行时,尾水管内会形成不稳定的螺旋涡带流动,导致严重的流量不平衡,进而影响系统动态特性.获取尾水管内完整的气液两相流动,是分析涡带生成和发展机理从而对其进行有效控制的基础.为此,本文突破传统测量技术在气液两相流测量中的局限性,结合粒子图像测速和脉冲阴影技术,同步测量液相速度场和两个垂直方向的涡带形态.分析不同涡带形态的演化过程,进一步通过图像处理获取螺旋涡带的直径和空间信息,实现单螺旋涡带的三维重建,得到单螺旋涡带清晰的三维形态和旋转进动过程.最后对尾水管内呈现单螺旋涡带时的液相速度场进行分析,并将液相速度场与涡带的三维形态进行空间关联分析.实验研究表明:尾水管内涡带呈现单螺旋、双螺旋、气芯堆叠3种形态的不稳定循环流动演化,单螺旋涡带局部一分为二时,会转化为双螺旋涡带;单螺旋涡带局部螺旋升角不断减小时,会发生涡带堆叠破裂;尾水管内呈现单螺旋涡带时,涡带整体随液相主流绕中心轴线旋转进动,同时涡带自身局部存在绕某一轴线的旋转,涡带形态的螺旋旋向与整体旋转进动的螺旋旋向相反.流动根据轴向速度分为外围主流区和中心滞止区两部分,主流区和滞止区之间的剪切层卷起形成旋涡,液相旋涡的位置决定了螺旋涡带的空间形态.

The limitation of traditional measurement technology in gas-liquid two-phase flow measurement is broken through.The liquid velocity field and vortex rope morphology from two vertical directions were measured synchronically by using particle image velocimetry and pulsed shadowgraphy technique.Experimental measurements show that the vortex rope in the draft tube presents three kinds of unstable circulation flow evolution,single spiral,double spiral,and overstocked rupture.When a single spiral vortex rope is partially split into two,it becomes a double spiral vortex rope.When the local spiral rise angle of a single spiral vortex rope decreases,it becomes an overstocked rupture.When there is a single spiral vortex rope in the draft tube,the vortex rope rotates precession around the central axis along with the liquid main flow,and the flow is divided into two parts,the outer main flow zone and the central stagnation zone,according to the axial velocity.The shear layer between the main flow zone and the stagnation zone rolls up to form several vortices.The position of liquid vortices determines the spatial morphology of the spiral vortex rope.