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Analysis On Stability Control Measures Of Francis Turbine
Jun 20, 2017

3.1 perfect flow design of Francis turbine

On the one hand to consider improving the efficiency of Francis turbine, on the other hand to consider the phenomenon of pressure pulsation as much as possible. To ensure that the Francis turbine stiffness to meet the requirements of the circumstances, taking full account of the requirements of static strength, but also to avoid the resonance phenomenon. The appropriate increase in blade thickness and the blade and the crown, the lower ring weld arc transition radius, to try to avoid stress concentration, but also to avoid the appropriate measures to avoid the resonance zone to prevent the blade cracking. At present, the most widely used is computational fluid dynamics analysis (CFD) and model tests. Through the CFD and model test, the flow channel, especially the guide vane airfoil, the rotor blade airfoil and the discharge cone are optimized to avoid the occurrence of the Carmen vane, reduce the eccentric vortex of the tail pipe, and control the amplitude of the draft pressure Reasonable range.

3.2 reasonable choice of Francis turbine speed

At present, the design and research of Francis turbine is mainly based on the optimization of the speed of Francis turbine. In the 1980s model of mixed-flow turbines, a pressure pulsation with a large frequency characteristic was found. Most of the high-energy load pressures were characterized by frequent frequency conversions, about 5 times less, The best working time is about 88%. In some cases, the change of pressure pulsation will be as high as 30% of the net head. The pulsation under this pressure is very sensitive to the cavitation coefficient and the change of the downstream tail. During the study of the Francis turbine, The mouth of the outlet to the top of the tail of the pipeline will appear when the corresponding pressure pulsation is too large. Simply reduce the size of the turbine by the way to reduce the rotation speed of the rotor and the wheel is desirable, the choice of Francis turbine should follow the local hydrological situation and changes in the water situation comprehensive analysis of the data can be adjusted to optimize the operation of the machine Happening.

3.3 Adjust the flow of the rotor blades

The Carmen vortex frequency calculation formula can be used to reduce the boundary of the water flow and the position separated from the blade by reducing the blade thickness of the outlet portion of the rotor blade to improve the shape of the effluent portion in order to reduce the strength from the vortex. The experiment of the transitional section of the unilateral small circular shaft of the water outlet shows that the vibration of the smaller shaft is smaller, and the change of the water outlet of the Francis turbine is adjusted to the chamfering angle of 30-40 degrees Its more powerful repair adjustment.