Study on the flow and pressure pulsation characteristics in the hump region of pump- turbine based on C-shaped blade design

Abstract

The main part of a pumped storage power plant is the reversible pump-turbine. The unstable hydraulic behavior known as the “hump characteristic” can make the reversible Pump-Turbine less stable. Concurrently, unsteady factors like flow separation in the guide vane area and pressure changes in the leafless area between the guide vane and runner cause unsteady vortices to form in the flow channel, which greatly increases the likelihood of hump formation and reduces the unit's operational stability. The performance curve of the reversible Pump-Turbine runner blade may be efficiently altered by refining its shape. In order to improve the hydraulic properties of the reversible Pump-Turbine, a “C” type runner blade has been devised. The reliability of the numerical calculation approach is first confirmed by comparing the results of simulation tests with the numerical simulation of the original runner's unit speed and unit flow characteristics under various operating situations. Six distinct “C” type runners are then created for the first Pump-Turbine unit. The complete characteristic curves of many “C” type runners and the original runner are thoroughly compared, with particular attention paid to flow characteristics, eddy current behavior in the hump area, and “S” characteristic curve analysis. Ultimately, the best runner is chosen based on these comparisons. Additionally, there is a moderate improvement in the eddies in the leafless zone between the guide vane and the runner, as well as between the active guide vane and the fixed guide vane. Furthermore, the draft pipe's flow pattern has improved noticeably close to its design condition, with a notable decrease in the vortex band on its top portion. An ideal C-type runner was chosen for the examination of frequency domain diagrams in the bladeless zone, draft pipe, and runner in order to examine the pressure pulsation characteristics at the maximum operating point (0.85Q_d) inside the hump area. The maximum pulsation amplitude within the bladeless zone decreased by 24 %, the pulsation amplitude in the trailing tube decreased by 6.8 %, and the runner itself decreased by 30 %, according to the results. Without sacrificing rated pump-turbine operating conditions or performance features outside of “S” characteristic areas, these results show that the use of “C” blades may successfully reduce unstable flow phenomena inside hump zones. This study offers useful information for lowering hydraulic losses, enhancing the stability of hump areas, and eliminating unit pressure pulsations; as a result, it may be used as a benchmark to improve pump-turbine stability overall.