Research On The Unsteady Flows And Stability Of The Bulb Turbine

Due to the big variation of rivers flow in one years, many operation organizationsproposed that not only the on-com but also the partial load performance should be improvedin recent years, that is expanding the scope of the operation. Therefore, to deal with therequirements for performance of variable head and variable flow, cavitation performance andwater pressure pulsation for the hydraulic turbine was analyzed based on CFD method in thispaper.In this paper, comparison of model test results with CFD numerical results wasconducted for5-vane bulb turbine. It shows that the relation between unit flow QDHand unitspeed nDHof CFD prediction are in good agreement with model test results. It also proves theapplication of CFD method can also meet research requirement. The following research inthis paper used CFD numerical calculation results. In this paper, full port stationary flownumerical analysis of4-vane bulb turbine has carried on first, proposing the on-cam operatingoptimization about the flow between runner outlet and draft tube and finding the relatedcharacterization factors. Results provide technical support to design optimization of hydraulicturbine and prediction of on-cam. They could also offer a good initial calculating environmentto numerical calculation of unsteady flow in the bulb turbine.Full port unsteady numerical simulation calculation was conducted as to small-flowcondition,on-cam condition and big-flow conditions for bulb turbine with3,4,5vane. Theresults show that energy conversion is clear and orderly and energy transfer is reasonablefrom the inlet to the export in turbine of3,4,5-vane. Analysis of pressure distribution in vanefrom the hub to the tip shows that partial pressure is low at the tip of inlet negative pressuresurface for the three kinds of turbines. It could probably produce local cavitation, so attentionneeds to be paid to reasonable domestication for entry angle in runner tip during optimizationdesign.Pressure pulsation degree of two boundary surface flow has been mainly tested in thispaper. For the interface between guide vane outlet and runner vane inlet, under conditions ofon-cam, big-flow, small-flow, pressure pulsation distribution from runner hub to tip showsregularity in3,4,5-vane; the pulsation amplitude is within the requirements; probability of unstable phenomenon is small. For the interface between runner outlet and draft tube inlet, bigpressure change generates in the center of the draft tube of3-vane bulb turbine and the flow inthe draft tube cone tube and expanding tube is affected with decreased running stability index.From the research results in this paper, it can be seen that overall performance of thedeveloped3,4,5-vane bulb turbine is ideal, especially cavitation characteristic and stability isgood under performance of the off-design condition, of which performance is wanted to beimproved.3-vane turbine has less runner blades, so blade passage is hard to generate betweenblades, making the research and development of3-vane more difficult. The analysis resultswith3-vane in this study will provide effective technical support for subsequent development.