Decelerated Swirling Flow Control in the Discharge Cone of Francis Turbines
The decelerated swirling flow in the draft tube cone of Francis turbines is a complex hydrodynamic phenomenon, particularly when the turbine is operated at partial discharge. In this case, the self-induced instability of an incoming steady axisymmetric swirling flow evolves into a three-dimensional unsteady flow field, with processing helical vortex (also called vortex rope) and associated severe pressure fluctuations. The paper presents the development of a swirling flow apparatus designed to generate the same flow conditions as in a Francis turbine at partial discharge, with corresponding helical vortex breakdown in a conical diffuser. This experimental setup allows the investigation of a novel flow control method aimed at mitigating the processing vortex rope by injecting a water jet along the cone axis. Earlier investigations considered a high speed jet, with relatively small discharge, for stabilizing the flow. However, further parametric studies revealed that a jet with a discharge of up to 10% the turbine discharge and velocity close to the average value at the turbine throat is more effective for mitigating the quasi-stagnant central region associated with the vortex rope. It is shown in this paper that such a control jet can be produced by using a flow feedback method, where a fraction of the discharge is collected from downstream the cone wall and injected upstream along the axis without any additional energy input.
francis turbine vortez rope swirling flow control azial control jet flow feedback
Romeo Susan-Resiga Sebastian Muntean
Dept. of Hydraulic Machinery and National Center for Engineering of Systems with Complex Fluids Pol Hydrodynamics and Cavitation Laboratory, Center for Advanced Research in Engineering Science Romania
国际会议
The Fourth International Symposium on Fluid Machinery and Fluid Engineering(第四届流体机械与流体工程国际会议)
北京
英文
89-96
2008-11-25（万方平台首次上网日期，不代表论文的发表时间）