Energy loss and flow characteristics analysis of a model pump turbine in the S-shape region
In order to adjust the stability of the power grid,the pumped storage power station needs to start and stop frequently and operate under different working conditions.The pump turbine easily enters to the S character-istic region,which leads to the increase in unit vibration,and the unit interconnected failure.A model pump tur-bine was set as the research object in this paper.The entropy production theory was used to analyze the energy loss laws under different operating conditions in the S-shape region,and the relationship between the entropy pro-duction distribution and the internal flow structure was clarified.The total entropy production near the runaway condition is the largest,which is about 5.1 times of that in the design condition.The proportion of fluctuation en-tropy production is close to 80％.As the discharge decreases,the proportion of runner entropy production gradu-ally decreases,while the proportion of guide vane and draft increases.There is a significant vortex first appeared near the shroud of the runner inlet,leading to a high entropy production area in the vaneless region.The vortex gradually developed towards the hub and the tangential velocity increased when the pump turbine operates in the turbine break condition.A water ring was formed at the runner inlet,hindering the water flow into the runner.A high entropy production region with circular distribution appeared in the vaneless region.Under the reverse pump condition,the water flow collides with the counterclockwise rotating blades at the low-pressure side,which makes it difficult for the water to enter the interior of the blades and forms a large-scale reverse vortex structure.The double row cascade is filled with a large number of vortex structures,leading to an increase in the entropy production rate of the guide vane,and propagated towards the stay vane.
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