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Predicting unsteady behavior of a small francis turbine at several operating points

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Publication date: April 2019

Source: Renewable Energy, Volume 133

Author(s): Ahmed Laouari, Adel Ghenaiet

Abstract

The simulated pressure-time, recorded at several monitoring points through the components of a small Francis turbine, show that the rotor – stator interactions (RSI) cause strong pressure fluctuations and torque oscillations even for the best efficiency operating point (BEP). The pressure fluctuations frequency and the mode shape and their sequence are predicted. At the low discharge operating point the significant drop in the static pressure is distinguishable at the inlet of the runner. The amplitude of the dominant frequencies at the low discharge operating point are larger than at BEP, in addition to other captured frequencies related to the occurrence of the vortex rope in the draft tube. The pressure fluctuations occurring in the vaneless space tend to propagate beyond the runner outlet and are influenced by the interactions between the runner and the draft tube. At most unstable operating conditions the pressure pulses within the runner passages are mainly related to RSI and channel vortices.

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