Research on the runner characteristics of Francis-turbine under power generation to no-load condition
As hydropower stations gradually shift to load-regulated operation,the increase in the operating time of turbine in transitional conditions will seriously affect runner performance.This paper aims at studying the fluid-solid coupling correlation characteristics of runner,wherein SST k-ω turbulence model and the fluid-solid coupling method are applied to solve the flow field and structural field,respectively.The results show that the main frequen-cies of pressure fluctuation in the runner are pass frequencies of blades and guide vanes,as well as their multiple frequencies.The pressure fluctuation frequencies of all monitoring points in the runner have similar amplitudes at 30fn and 60fn,and the amplitude range gradually narrows as the guide vanes close.The main frequencies of vortex structures are 64fn and 68fn in the runner,which pulsation energy attenuates along the streamlines.The blade pas-sage vortex reaches the runner outlet at 0.4QBEP,the vortex volume in the runner first increases and then decreases as the load continues to reduce.After 0.4QBEP,the flow separation phenomenon on the pressure surface at the inlet of runner intensifies as the decrease of β(the absolute velocity angle),further horseshoe vortex with high turbulent kinetic energy appears in the flow channels,which is accompanied with flow around blade outlet.The vortex core at runner outlet start to split at t=7 s(0.2QBEP),then vortices in each runner passage form sheets and block the flow channel.In the structural field,the increase of equivalent stress at blade inlet is caused by the flow impact with smaller β,the horseshoe vortices in runner channels correspond to long and narrow zones with low equivalent stress.The equivalent stress(4 MPa)and deformation(4.3 μm)at the runner outlet are the maximum,because of dual effects from vortex core splitting at runner outlet and cavity vortices in the straight section of the draft tube.Last but not least,it founds that the equivalent stress has a linear relationship with torque and flow in the approxi-mately one third of the area in front of the runner passage,whereas it is cubic functions in the last two thirds of the runner path.The deformation is also has a linear relationship with torque and flow in the load-dominated area,while it is a quadratic function in the return-dominated area.The above relationships between flow field and struc-ture field need further validation in other hydraulic machinery,which will be the next work for the authors.
Francis-turbinerunnerpower generation to no-load conditionturbulent kinetic energyvibration mode
万方数据
维普
