Abstract
In this paper, we introduce a novel passive control method to mitigate the unsteadiness effects associated to the swirling flows with self-induced instabilities. The control method involves a progressive throttling cross-section flow at the outlet of the conical diffuser. It adjusts the cross-section area with a diaphragm while maintaining all positions of the circular shape centered on the axis. It improves the pressure recovery on the cone wall while the pressure fluctuations associated with the self-induced instability are mitigated as it adjusts the cross-section area. It can adjust the diaphragm in correlation with the operating conditions of the turbine. We investigated the passive control method on a swirl generator, which provides a similar flow as a hydraulic turbine operated at a partial discharge. The plunging and rotating components are discriminated using the pressure fluctuation on the cone wall to provide a clear view of the effects induced by this passive control method. As a result, the novel proof of concept examined in this paper offers valuable benefits as it fulfils a good balance between the dynamical behavior and the hydraulic losses.
Highlights
Nowadays hydropower is perceived as a mature technology but it has to face to new requirements more challenging than ever: the stochastic nature of renewable energy sources, irregular market requirements for energy, climate changes, constraints and environmental concerns [1]
We introduce a novel passive control method to mitigate the pressure fluctuations associated to the vortex rope, relying on the latest knowledge gained from an extensive analysis of the swirling flows
The experimental investigations are performed on a swirling flow test rig
Summary
Nowadays hydropower is perceived as a mature technology but it has to face to new requirements more challenging than ever: the stochastic nature of renewable energy sources (wind, solar), irregular market requirements for energy, climate changes, constraints and environmental concerns [1]. The hydraulic turbines have to operate over a wide range [2,3] under a fast change of the parameters to compensate the fluctuating part delivered in the electrical grid by the renewable energies. Several times, these requirements implied transient phenomena (e.g., load acceptance, load rejection, start-stop, emergency shutdown, spin no load, total load rejection) in operation [4,5,6,7]. Along the upstream passage of the hydraulic turbine, the potential energy of the water available in the upper tank is converted into kinetic energy. A fraction of this residual energy is converted back into potential energy along to the draft tube [9]
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