Numerical Simulation And Prototype Test Research On High-head Hydropower Station's Hydraulic Characteristics

Most of the basins in the southwestern region are mainly constructed by High-head Hydropower Station.Compared with the conventional turbines,the operational stability problems induced by hydraulic factors are particularly prominent.Taking a high-head hydropower station as an example,this paper uses prototype test,three-dimensional unsteady value simulation and one-dimensional coupled numerical simulation method to study the hydraulic characteristics under different head and flow conditions.It has certain guiding significance for the study of High-head Hydropower Station's hydraulic characteristics safety.The main research contents of this paper are as follows.(1)Based on the prototype test of a hydropower station on the Yalong River,the test data covers six head conditions of the turbine from 155 m to 235 m,and the relative flow range is from 0.2 to 1.Analyze the pulse pressure monitoring data at the end of the volute and the inlet of the draft tube.The test results show that when the turbine is operated at low head conditions of 155 m,165m and 185 m,the pressure pulsation is more severe.The relative pulsation of the volute and the draft tube increases first and then decreases with the increase of the flow rate.When the relative flow is close to 0.6,the maximum relative amplitude reaches 5%;Under the water heads of 205 m,225m and 235 m,the relative pulse pressure of the volute increases with the increase of the flow rate,and the maximum relative amplitude is 1%.The relative pulse pressure of the draft tube decreases with the increase of the flow rate,and the maximum relative amplitude is 3%.(2)The three-dimensional numerical simulation of the prototype turbine was carried out using Fluent finite element software.The research conditions included three types of heads: 155 m,165m and 185 m,and five kinds of flow of guide vane openings of 100 mm,140mm,220 mm,310mm and 360 mm.The 12 monitoring point pulse pressure data of the volute,vane and draft tube were extracted for analysis.The research on the opening degree of the fixed head shows that the symmetric monitoring point of the small guide vane is due to the rotation of the eccentric vortex.The pressure pulsation results have a phase difference,the frequency is 0.525 times,and the maximum pulsation point appears downstream of the straight cone.The absolute value of pulse pressure is 70 kPa;When the vane opening degree is more than 200 mm,there is no eccentricity in the vortex belt,the pulsation phase difference of the symmetric measuring point disappears,and the pulsation frequency is 0.8 times.The study of the constant vane opening degree shows that the turbine is unstable in the vicinity of the guide vane opening of 140 mm,and the sensitivity of the measuring points at different positions is different,which is expressed by H/H.The draft tube area H/H = 4%~6%,and the guide vane area H/H = 0.9%~1%,it runs in unstable areas,and the draft tube pulsation is more affected by the water head.(3)Combined with VB language and Fluent calculation software,a set of one-dimensional and three-dimensional coupled numerical simulation methods are proposed,and the simulation analysis and application of low water level and small opening degree conditions with H=165m and guide vane opening a=140mm are carried out.Compared with the direct three-dimensional unsteady value simulation,the numerical simulation results of one-and three-dimensional coupling are close in frequency,and the pressure value is higher by 100 kPa,which is closer to the measured value.Analyze the amplitude and frequency characteristics of pulse pressure to obtain the operation characteristics of the turbine with low head and small opening degree: the low pressure zone formed by the straight cone section of the draft tube will rotate with the rotation of the rotor,and it will collide with the pipe wall,and the generated pressure pulsation will propagate in the draft tube.The frequency remains basically the same,but the energy is reduced;the transmission energy in the unit is small,and the volute and the vane are mainly composed of dynamic and static interference high-frequency pulse pressure.