Experimental Study On Influencing Factors Of Draft Tube Pressure Pulsation Of Francis Turbine

In recent years,with the expansion of single unit capacity of hydropower units,the operation stability of hydraulic turbines has attracted more and more attention.Draft tube pressure pulsation is one of the main causes of unstable operation of the unit.It will cause mechanical vibration,damage turbine components and affect the stable operation of the unit.The research contents of this paper are as follows:(1)This paper expounds the formation mechanism of draft tube pressure pulsation from the theoretical level,and explains several measures that can effectively improve draft tube pressure pulsation.(2)Combined with the model test of Francis turbine in the unit expansion project of a power station,seven test schemes(primary scheme)composed of different types of discharge cones and an air replenishment frame are formulated,and the variation of pressure fluctuation amplitude with flow is studied under three characteristic heads(28.1m,38 m and 43M).Through the comparison between different schemes,it is found that the pressure fluctuation amplitude of the two schemes is lower.(3)Optimize and improve the above two schemes,redesign the new air replenishment frame and water discharge cone,and formulate two new schemes: air replenishment frame 3 and air replenishment frame 3 + water discharge cone 8.The two new schemes are compared,and the scheme with the smallest pressure fluctuation amplitude is selected as the final scheme.Based on the final scheme,the influence of water head on the amplitude of pressure fluctuation is studied;The air replenishment test of draft tube is carried out,and the influence of air replenishment on the amplitude of pressure fluctuation is studied.(4)On the basis of the final scheme,Lab VIEW software is used to analyze several working points with large pressure fluctuation amplitude under the four heads of 28.1m,32 m,38m and 43 M in time-frequency domain.