| Hydropower is the largest clean energy.Among the four categories of hydropower sets,impact hydropower sets have more obvious advantages than other types of hydropower sets,which are reflected in low hydraulic construction cost,less relocation,and the use of water head exceeding 1000 meters.The multi-nozzle hydraulic generating set is the development trend of impact hydraulic generating set.The runner is an important part of the hydraulic generating set and the core of energy conversion.With the increase of the operating water and number of nozzles,the flow field inside the runner becomes more complex and difficult to analyze.The number of transient loads of the jet in a cycle increases,and it is more likely to crack or even fracture in the weak area of the runner.Therefore,the safety and fatigue damage of runner are the key issues concerned by the design and operation departments of hydropower units.Six-nozzle pelton turbine is the development trend of impulse hydraulic generating unit,and the study of fatigue analysis is very important to ensure the safety of the unit.Based on six nozzle turbine in a power station as the research object,based on the fluid-structure coupling technology to carry out the jet impact on water turbine runner internal flow field of the research,the runner at work on the mechanical performance study of runner and jet flow induced vibration,fatigue life prediction under transient loading runner,to the status of hydropower unit provides the theory basis for inspection,maintenance and life prediction.The specific contents are as follows:1.Transient numerical calculation of flow field of six-nozzle pelton turbine.The formation mechanism of free jet in pelton turbine is studied and the flow field of free jet in runner is analyzed.The transient load of the jet on the runner and the distribution law of the surface pressure of the bucket were obtained.2.Study on mechanical properties of runner.Based on the calculation results of transient flow field,the fluid-structure coupling technology was used to study the mechanical properties of the runner under transient load,and the dangerous parts of the runner’s water bucket were found and the corresponding mechanical properties data were obtained.3.Research on vibration characteristics of runner.The rotor vibrates under the action of hydraulic excitation force,and the vibration characteristics of the rotor are studied to reveal the vibration frequency and mode rule of the rotor under the rated condition and flying condition.4.Fatigue life prediction of runner.Based on the stress-time history data obtained,the fatigue life of the six-nozzle pelton turbine under rated conditions is discussed by using the structural fatigue failure theory,which provides suggestions and references for the operation and maintenance of hydropower stations.The research shows that: under the action of the transient load of the jet,there is a negative pressure on the back of the top of the bucket,which is easy to cause cavitation damage;the runner is subjected to obvious transient stress under the combined action of the transient load and centrifugal force,and its dangerous parts appear in the water.On the front and back of the bucket root,there is stress concentration at the edge of the water dividing blade,and the top of the bucket is deformed greatly,which is prone to cracks and fractures,which is consistent with the damage of the runner on site;under the action of the jet,the natural frequency of the runner is much higher than that at rated The rotating speed of the runner under the working condition is close to the rotating speed under the runaway working condition;therefore,the vibration is an inducement for the damage of the runner,but the damage of the bucket root of the runner is mainly caused by the transient load of the runner.Fatigue damage caused;the predicted life of the runner of the unit under rated conditions is 48160 h,which can be used as a reference for the inspection and maintenance of the hydropower station. |
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