Effect Of The Guide Vane Pitch Circle Diameter And The Clearance Of The Lower Ring On The Performance Of The Francis Turbine

For Francis turbine,the relative position of movable guide vane,fixed guide vane and runner directly affects the internal flow of distributor and runner.Complicated turbulence such as leakage vortex and leakage flow in the runner gap can also easily affect the performance and stability of the turbine.This paper takes the HLX180-LJ-145 Francis turbine of Wenjing hydropower station as the research object,adopts CFD technology,based on N-S equation,SST Turbulence Model and Zwart cavitation model.Put forward 5 kinds of movable guide vane distribution circle diameter schemes and 5 kinds of lower ring clearance schemes,considering different flow conditions.The energy characteristics,cavitation performance and stability of the units are compared to find the optimal matching between runner and other flow passage components.The results of this study can be implemented in the capacity expansion and reconstruction of hydraulic turbines,and have certain reference value for the structural design of hydraulic turbines.Related research results include the following parts:1)For the Francis turbine studied in this paper,when the range of D0/D1(guide vane pitch circle diameters/runner diameter)is 1.12?1.15,the efficiency of the turbine increases monotonically with the increase of the Guide Vane Pitch Circle Diameter,and the energy loss of the guide vane and runner decreases with the increase of the diameter of the distribution circle of the guide vane.The Zwart cavitation model is introduced to calculate the whole flow passage of Francis turbine.This paper describes the evolution process of cavitation in the runner under various flow conditions,and compares the cavitation performance of the turbine under the same guide vane pitch circle diameter.It can be found that under the same flow condition,the number and volume of the cavitation on the surface of the runner blade are reduced and the cavitation performance of the unit is improved by increasing the guide vane pitch circle diameters.2)Through unsteady calculations,we can study the generation mechanism and change law of pressure pulsation in the bladeless zone between the movable guide vane and the runner.It is found that when the unit is operated under two flow conditions of design conditions and 0.6Qd,the activity increases The diameter of the guide vane distribution circle can weaken the dynamic and static interference between the movable guide vane and the runner area,reduce the pressure pulsation amplitude of the bladeless area between the movable guide vane and the runner,and improve the stability of the unit operation.3)The lower ring clearance of the runner is in the range of 0.4?1.3mm,and the influence of the lower ring clearance on the energy characteristics,internal flow pattern and pressure pulsation in the flow channel of the Francis turbine is explored.It is found that when the unit is operating under non-design flow conditions,the clearance of the lower ring increases and the efficiency of the turbine decreases.The leakage rate of the gap increases with the increase of the lower ring gap,and the average flow velocity and vortex intensity in the gap increase with the increase of the lower ring gap.4)By extracting the pressure pulsation results of the monitoring points inside the gap,the leafless area and the surface of the runner blades,it can be seen that the pressure pulsation amplitude of the monitoring points inside the gap and the leafless area increases with the increase of the lower ring gap.When the turbine is working under small flow conditions,reducing the lower ring clearance can reduce the pressure pulsation amplitude at the monitoring points on the runner blade surface;when the turbine is running under design conditions and large flow conditions,increasing the lower ring clearance can reduce the pressure pulsation amplitude at the monitoring point on the blade surface.5)The pressure fluctuation at the measuring point in the draft tube mainly comes from the uneven pressure field caused by the unstable vortex.When the unit is operating at low flow rate,the strength of the vortex band in the tube can be weakened by reducing the gap between the lower rings,and the pressure fluctuation amplitude at the measuring point on the draft tube wall will be reduced.When the unit operates under the design condition and large flow condition,the monitoring points in the draft tube decrease with the increase of the clearance value.The selection of the clearance size of the lower ring should be combined with the actual operating conditions of the unit.If the turbine vibrates strongly when operating under small flow conditions,the vibration caused by hydraulic factors can be reduced by reducing the clearance of the lower ring.If the unit has strong vibration when operating under design conditions and large flow conditions,the lower ring clearance can be appropriately increased to improve unit stability.