Study On Flow Characteristics Of "S" Zone Of Water Pump-turbine And The Scheme Of Misaligned Guide Vanes

With the development of pumped storage power stations,the reversible water pump-turbine,an integrated unit,has gradually become the first consideration for commercial energy storage power stations because of its structure,operation mode and benefits,which are better than ordinary turbines.And with the increasing capacity of the power station,the requirement for stable and reliable operation of the unit is higher and higher.However,reversible units are prone to enter the characteristic area of "S" curve in the process of starting and load rejection,leading to the unstable operation of units and the problem of grid connection difficulty.The method of misaligned guide vanes using at the present stage can effectively improve or even avoid the "S" characteristic of the pump-turbine,but the improvement effect of different guide vane layout schemes on the "S" characteristic is significantly different.Therefore,in this paper,the flow characteristics of the internal flow field of the water pump-turbine,the stress of hydraulic components and pressure pulsation are analyzed and studied,and the reasonable misaligned guide vanes opening and misaligned guide vanes layout schemes are obtained.The main research contents and results are as follows:1.The numerical calculation model of the whole flow channel under the synchronous guide vane and the non-synchronous guide vane of the reversible water pump-turbine was established.The geometric model of the active guide vane was obtained.And the fluid domain was divided by structured grid.The reliable numerical calculation model was obtained.Reasonable boundary conditions were set.2.At a small flow condition,the operating point in the "s-shaped" region is selected to carry out unsteady numerical calculation on the model pump-turbine.The 3d unsteady numerical calculation results of the whole channel with different opening degrees of the synchronous guide vane were compared in detail,and the results were compared with the experimental results for verification.The internal flow characteristics of guide vane-vaneless region-runner region with different opening degrees of movable guide vane were analyzed,and the stress of the runner was quantitatively analyzed.Results show that under the small flow condition,because the flow direction at the outlet of the movable guide vane has a relatively large angle of impact with the inlet of the runner,and a high-speed water ring is formed in the vaneless area at the outlet of the guide vane and the inlet of the runner,which produce a large number of vortex structure and blocks the flow of water,lead to the formation water pump-turbine "S" characteristics.3.Four groups of pump-turbine models with different degrees of guide vane opening were selected for 3d unsteady calculation of the whole flow channel,and the internal flow state between the movable guide vane and the runner area,the stress of the runner and the pressure pulsation of the draft tube under different guide vane opening were analyzed.The results show that the "S" characteristic can be improved by increasing the opening of the misaligned guide vanes under the premise of ensuring the stable operation of the unit.Different synchronous guide vane opening degrees correspond to different optimal opening degrees of the misaligned guide vanes.At a small flow condition,the opening of the misaligned guide vanes is 3 times that of the synchronous guide vane,which is the ideal ratio of opening.Which has the optimal effect to improve the "S" characteristic.4.The 3d unsteady numerical calculation of the whole flow channel for the pump-turbine model with the different pairs and arrangement modes of the misaligned guide vanes is carried out under the reasonable opening degree of the misaligned guide vanes.And through analysis the movable guide vane to the runner area of the internal flow characteristics and the runner stress.The results show that under the condition of small flow,opening two pairs of guide vanes and the symmetrical arrangement of misaligned guide vanes have the optimal effect on improving the "S" characteristics.