Analysis of pressure pulsation in Francis hydraulic turbine with misaligned guide vanes

In this paper,a simulation of the three-dismensional unsteady turbulent flow in the whole passage of a model Francis turbine by adopting a realizable k-e turbulence model is presented.The model is verified by using experimental results,and pressure pulsation of the model turbine with misaligned guide vanes(MGV) device is calculated.Two MGV with five different MGV opening angles are chosen to analyze the influence of MGV on pressure pulsation in the spiral case,guide vanes,blades and draft tube.The computational and experimental results show that the rotational frequency of the vortex rope does not vary with MGV opening,while the amplitudes of differernt frequencies vary with MGV opening differently.The dominating frequency in the runner is the difference between the runner frequency and the rotational frequency of the vortex rope.A new frequency equal to the product of runner frequency and the number of MGVs appears in the runner,and the amplitude of this new pressure pulsation increases with the difference between the MGV opening and the other guide vanes opening.The MGV changes the peak-to-peak amplitude in the same way as the guide vanes without MGV,therefore,MGV can be adopted to ensure the stability of turbine with little changes of output.