Blade Crack Initiation/propagation Prediction And Wet Modal Analysis During Cavitation Of The Turbine Runner

As the key part of the mechanical and electrical systems in a hydropower plant,Unlike the conventional unidirectional turbine which is used for a consistently operation,the reversible pump-turbine has to startup and stop frequently even in one day.During the complex operating condition changes,sometimes huge hydraulic excitations will be induced.Meanwhile,cavitation is a very common phenomenon in runner channel,particularly in part-load conditions.Therefore,these events have non negligible influence on the dynamic responses and fatigue life of the pump-turbine.This thesis analyzed the fluid characteristics and structural strength of a pump-turbine runner under various stable and transient events.Taking the crack initiation and propagation processes into account respectively,the complete fatigue lifetime of the runner was estimated.Then,the prediction of this runner modal response change under various cavitation conditions was carried out.Related research results have important theoretical significance and engineering practical value.A new approach pertaining to the pressure frequency domain analysis in fluid machinery field was proposed,which is named as pressure shape identification approach(PSI).The PSI algorithm shows a strong anti-noise-interfere ability.This is a very helpful and practical tool to identity the main frequencies in the turbine flow field.The most advantage of PSI is that it uses 3D pressure fluctuation phase graphs to reproduce the induced location,strength and propagation of single frequency components in the whole flow field.Through PSI,the atypical frequency of 2.56 fn and others are explained reasonably.Based on the local stress and strain fatigue theory and fracture mechanics,the complete fatigue estimation method of the turbine runner was proposed.The crack initiation and crack propagation lives were evaluated under various stable and transient events.The complete fatigue estimation method provides an effective analysis technique to assess the units' safe operating conditions and the maintenance arrangement for a power plant.Wet modal analysis approach of the runner in vapor-liquid two phase medium was established by finite element method.This numerical approach was validated through comparison of corresponding simulations with the experimental results of a NACA0009.The results showed that each mode could be transited according to the different vaporliquid percentage.The modal transition line was found to explain these changes.The wet mode changes under various cavitation conditions were analyzed in detail,revealing the cavitation evolution influence mechanism on turbine runner modal characteristics.The results indicated that the pump operating conditions have stronger influence on turbine runner modal characteristics than the turbine operating conditions.This is because the vapor cavities are closer to the runner wet surface in pump operating conditions than turbine operating conditions.Taking the cavitation into account for turbine runner modal analysis,it is able to obtain more comprehensive results on runner dynamic characteristics and fatigue performance in different operating conditions.