Analysis On Pressure Characteristics Of Vaneless Region In High Head Francis Pump Turbine

In order to meet the demand for electricity in recent years, a number of newlarge-scale thermal power plants, nuclear power plants have been built. Theproduction of these large-capacity units put forward a higher requirement for grid’sstability and rapid response characteristics and must establish ancillary conditioningsystem. Pumped storage power station, with its ability of frequency modulation andpeak regulation, comes to be the best choice, following the attention on stability ofpump turbine. Among the large numbers of factors that affect the stable operation,the strong Rotor Stator Interaction and complex pressure fluctuations in vanelessregion are the main reasons causing unstable operation, even lead to vibration, noiseand blade cracks. Therefore, it is necessary to study pressure characteristics andpulsation mechanism in vaneless region deeply, in order to provide a reference forthe design and stable operation of the pump turbine.For studying pressure characteristics of vaneless region, this thesis use CFD tosimulate model and prototype of a pumped storage power station in China under thesame unit speed, different guide vanes’ opening angle and guide vane’s swingprocess of model in turbine mode, pressure pulsation has been analyzed in detail, themain contents are as follows:Firstly, according to the actual operating points of prototype, the modelsimulation was conducted under six different guide vane’s openings, externalcharacteristic curves and pressure fluctuation amplitude changing with vane’sopenings were obtained, also compared with the experimental data. Then this thesisgave the theoretical prediction of pressure pulsation frequency in vaneless regionwhich was verified by numerical simulation later, analyzed pressure fluctuationcharacteristics of optimum operating condition with its propagation regulation, andmade a brief analysis on pressure pulsation with the variation of the guide vane’sopening.Secondly, the prototype simulation was made under50%load, optimumoperating condition and full load, then the results were compared withcorresponding similar conditions of model in detail, also the differences andtranslation relationship of pressure pulsation amplitude and frequency betweenmodel and prototype were studied.Thirdly, this thesis used moving mesh method for model calculation, took18degree as the starting opening and simulated pressure fluctuation characteristicsduring guide vanes swing around1degree. Amplitude, time domain and frequency domain characteristics under different guide vanes rotational states were studied. Atlast, this thesis made a comparative analysis of pressure fluctuation in vanelessregion between the entire swing process and guide vanes fixed opening process.The results show that, the main pressure pulsation frequencies in vanelessregion are runner blade passing frequency and its harmonic frequencies, also thereexists other frequencies coming from runner and draft tube. It’s easier to propagateupstream for vaneless region pressure fluctuation, but amplitudes of frequencycomponents attenuate differently. Different guide vane openings have a significantimpact on the vaneless region pressure pulsation characteristics. Model andprototype contain nearly the same frequencies under similar conditions, but the themagnitude of amplitudes are different and there is no obvious translationrelationship between model and prototype. During guide vanes swing process, thefrequency components under9times runner frequency of vaneless region are muchmore rich, the pulsation amplitude relative to fixed opening increased significantly.