2019 Volume 12 Issue 3 Pages 217-227
Increased penetration of intermittent energy resources disturbs the power grid network. The frequency band of the power grid is normally controlled by automatic opening and closing of the guide vanes of hydraulic turbines. This has increased the number of startup and shutdown cycles as compared to the defined ones for the normal operation of turbines. Turbine startup and shutdown induced a higher level of pressure fluctuations and unsteadiness in the flow field, decreasing its expected life. This paper presents the pressure and velocity measurements performed on a Francis turbine model during startup and shutdown. The pressure measurements were performed in the vaneless space and draft tube and two-dimensional particle image velocimetry measurements in the cone. The turbine operations from a standstill (no flow) and high load were considered to perform the startup and shutdown, respectively. The frequency of rotor-stator interactions and standing waves were well captured in the spectrograms of pressure signals. The signature of rotating vortex rope frequency was also observed in the spectrograms. A huge disturbance in the draft tube flow was observed due to these transient operations. The flow at the center was mainly dominated by the stagnant, separation and recirculating regions.
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