Study of vortex rope for the flow field pulsation law

Abstract

When a hydro turbine deviates from the best efficiency conditions and carries the partial load, the helical vortex rope appears in the center of the draft tube. It will cause the unstable operation. In order to study the characteristics of the vortex rope more clearly, this study monitored the pressure pulsation of the draft tube through large eddy simulation. The temporal-spatial features of spiral vortex rope are well analyzed and visualized by pulsation tracking network (PTN). The results show that the draft tube vortices can be divided into spiral vortex, fragmented vortex and reunited vortex. The frequency of 1.9 Hz is the dominant frequency, which is located in the center of the spiral vortex rope. The area proportion of 1.9 Hz is reduced to 3.63% at the outlet. There are three types of phase difference characteristics. Type-1 is through the center and the whole road section. Compared with linearity, S-shape represents the radial hysteresis of circumferential pressure wave propagation. Type-2 is similar to a circle. Type-3 is similar to the combination of Type-1 and Type-2. This study is of great significance for the design and operation stability of hydro turbine.