变速水泵水轮机抽水工况变速增负荷过程流动特性OA

To reveal the influence mechanism of variable-speed regulation on the clearance flow cha-racteristics of pump-turbines,a prototype variable-speed pump-turbine was taken as the research object.A three-dimensional fluid domain model including the upper crown and lower ring clearances was established,and the clearance flow characteristics were analyzed under two typical pumping condi-tions(i.e.,maximum head and minimum flow rate,and minimum head and maximum flow rate)and during the variable-speed load-increasing process.The results show that under the low head and large flow rate condition,the vortices in the spiral casing,upper crown clearance and draft tube cone are more prominent.The pressures on the upper crown surface and lower ring surface of the runner exhibit a circumferential distribution and increase gradually along the radial direction.The fluid in the clea-rances presents a turbulent state under high velocity and pressure gradients,and obvious backflow oc-curs at the labyrinth seal.During the variable-speed load-increasing process,with the synchronous in-crease of rotational speed and guide vane opening,the power increases approximately linearly.The vor-tices in the flow passages of stay vanes and guide vanes gradually diminish,and the flow pattern in the passages improves progressively.Meanwhile,the flow pattern in the lower ring clearance is superior to that in the upper crown clearance,but no load-dependent regularity is observed.The axial hydraulic thrust acting on the runner is upward,with the maximum and minimum values of 1.912 02×106 N and 1.700 16×106 N,respectively,and no linear correlation with rotational speed is detected.The research findings can provide theoretical support for the optimal design and safe operation of variable-speed pump-turbines.