Influence of Upstream Disturbance on the Draft-Tube Flow of Francis Turbine in Part-Load Conditions

Abstract: The rapid increase of renewable energies (e.g. wind and solar energies) requires hydroturbines (e.g. large-scale Francis turbines) to be operated at part load more frequently in order to improve the stability and flexibility of the power supply system. Therefore Francis turbine often suffers from severe low-frequency and large-amplitude hydraulic instability, which is mostly pertinent to the unsteady vortex-rope precession in the draft tube. The influence of disturbances in the upstream on the draft-tube vortex flow is not yet well understood. This speech will introduce the influence of upstream disturbances on the vortical flow in the draft tube with the analysis of paramount parameters (e.g. the operational condition, the swirl number and the inlet velocity profile). The possible interaction mechanism between the swirling vortex rope and the upstream disturbances will be further discussed. Special implications for the future design of large-scale turbines will be shared and discussed.