Analysis Of Pressure Fluctuation Of 1000MW Francis Turbine

With the development of energy industry,and the maturing of technology,China's hydropower industry has entered a large power grid,large units,high voltage and highly information development period.The hydraulic unit is the core equipment of the hydropower station,in which the turbine is the core of the energy conversion of the hydraulic unit.Due to the head adaption and a wide range of flow,Francis turbine occupies a large proportion in practical engineering applications.The real machine of Baihetan Hydropower Station which in built is Francis turbine.As soon as the power station is completed,it will achieve the breakthrough of a million kilowatt-class stand-alone capacity,becoming the second largest hydropower station after the China's largest hydropower station,the Three Gorges Power Station.Due to the limitation of running conditions and the actual demand of the power grid,the Francis turbine often runs under the deviation from the design conditions.The problem of the stability of the Francis turbine has been the focus of the industry research.This paper is based on the model turbine of Baihetan hydropower station,by using the numerical simulation method to calculate the internal flow mechanism under different unit speed and different opening degrees.The internal flow mechanism is analyzed in detail,and the characteristics and propagation law of pressure fluctuation are obtained.The main contents of this paper are as follows:Firstly,Under the same guide vane opening?a₀ = 8.47mm?and different unit speed,the unsteady calculation is carried out for different working points.Not only the pressure fluctuation characteristics in different flow areas,but also the propagation law along the flow direction is studied.The influence of rotational speed of runner to frequency and amplitude of pressure fluctuation is also obtained in this research.Secondly,under the same unit speed(n₁₁ = 58.8r / min),the guide vane opening is changed and the unsteady calculation is carried out for different working points.Changing the pressure fluctuation time domain data of each monitoring point into frequency domain data,we can get the pressure fluctuation characteristics and the propagation law along the flow direction.Thirdly,under the changing flow condition,the trend of pressure fluctuation in each basin is obtained.The similarities and differences of pressure fluctuation characteristics are analyzed and compared between the constant flow condition and the changing flow condition.The results of this study show that,the main frequency of pressure fluctuation is affected by the guide vane opening and the rotational speed of the runner.It propagates both upstream and downstream,and decreases or increases along the whole channel.The amplitude of the pressure fluctuation increases with the increase of the speed under small guide vane opening conditions.Under small guide vane opening conditions,the pressure fluctuation performs the low frequency of the vortex rope in the draft tube when the runner speed is low or high.It performs blade passing frequency and its harmonics in vaneless space when the runner speed is medium.While under the large guide vane opening,the amplitude of the pressure fluctuation decreases in general,which indicates that the smaller the guide vane opening is,the more obvious the pressure fluctuation characteristic is,the more violent the pressure fluctuation is.Under the changing mass flow condition,the continuous increase of the mass flow has a great influence on the amplitude of the pressure fluctuation,and obviously increases compared with constant mass flow condition.