Experimental Investigation of the Action Mechanism of the Draft Tube Pressure Pulsation in Prototype Francis Turbines

The draft tube pressure pulsation (DTPP) in the Francis turbine could decrease the whole stability of the hydropower unit and cause fatigue damages. In addition, the propagation and action mechanism of the DTPP in the Francis turbine have not been fully clarified. So, three prototype Francis turbines with capacities of ۵۵ MW, ۲۰۰ MW and ۶۰۰ MW were used as objects, and a series of field experiments have been carried out by us. Fortunately, some valuable results have been obtained. Firstly, the frequency components in DTPP were found to be mainly ۰.۲۵ fn and its multiples. Secondly, the propagation characteristic of DTPP was found and verified in the large Francis turbine for the first time. Only the component with a frequency of ۰.۲۵ fn could be propagated to the upstream flow channel, and it was identified as the 'synchronous pressure pulsation'. Thirdly, it has been verified that the shaft vibration can be affected by the synchronous pressure pulsation. Furthermore, a novel index for evaluating the impacts of the DTPP is proposed and validated. These results could provide guidance for the operation optimization and numerical simulation studies for the Francis turbine.

کلیدواژه ها:

Hydropower station ، Impact quantification ، Synchronous hydrodynamic surge ، Mechanical stability ، Hydraulic stability