Study On The Karman Vortex Characteristics And Control Method In Francis Hydro-turbine

The internal flow can directly effect the efficiency and stability of Francis turbine.Flowing separation and cavitation and pressure fluctuation can be caused when the flow deviates from the design condition.These problems are the main factors influencing the operation stability.Among them,the Carmen vortex has great influence on the stability of the turbine,and the problem caused by the vortex on the outlet edge of stay vane,which seriously endangers the o peration safety of the turbine.At present,both in foreign and domestic manufacture it is very hard to accurately predict the resonance phenomenon of flow components of the turbine that caused by Carmen vortex.In the structure design of the turbine,desi gners make a predictive calculation of Carmen vortex frequency that according to the Carmen vortex formulation or engineering experience.When Carmen vortex resonance problems happens in power plant,the implementary remedial treatment usually based on the experience.Therefore,the flow components resonance problem caused by Carmen vortex has aroused the attention of the industry.This article establishes the geometry model of the spiral case and stay vane and guide vane of Francis turbine,determines the computational domain and mesh,and sets the initial and boundary conditions of the numerical simulation.By using the large eddy simulation method,the Carmen vortex frequency of the stay vane and guide vane of the model turbine is calculated under specifi c operating conditions.The Carmen vortex frequency of stay vane and guide vane of prototype turbine is calculated by using the conventional calculation method.The method of Carmen vortex treatment is determined by the model experiment and the actual engi neering case.The numerical simulation results indicate that the Carmen vortex of the model turbine is difficult to calculate,the conventional turbulence model which be used in the calculation of the Carmen vortex can not simulate the vortex flow of model turbine.To calculate Carmen vortex of stay vane and guide vane of prototype turbine indicate that the frequency range of Carmen vortex that under different operation conditions of prototype turbine is identified when the hydraulic design of model turbine has completed.To optimize the structure and form design of flow component is an important method to avoid the Carmen vortex in prototype turbine,it makes the natural frequencies of the components in the water to avoid the Carmen vortex frequency.Then through the model experiment and engineering practice problem this paper proposes a method to prevent and eliminate the Carmen vortex in turbine.