Influence of the hydrodynamic damping on the dynamic response of Francis turbine runners
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The dynamic behavior of Francis runners is of interest in the hydraulic machinery field since it is one of the most used type of hydraulic turbines for electricity generation. To evaluate the dynamic behavior of Francis runners, their natural frequencies have been studied extensively in the past. However, mode-shapes and damping ratios associated to those natural frequencies have not been studied in detail. The hydrodynamic damping, which is the damping induced by the surrounding fluid, plays an important role in the dynamic behavior of this kind of structures and it is challenging to be estimated. In this paper, an experimental investigation of a submerged Francis runner is presented. For this, a model of a medium head Francis turbine is used. The runner has been instrumented with a Piezo Electric Patch (PZTp), as well as with different accelerometers. The mode-shapes of the runner have been studied in detail in air and with the runner submerged in infinite medium of water and near a wall. Furthermore, damping ratios of every natural frequency have been obtained and compared for the different cases tested. Results have been also compared with a numerical model that includes the effects of hydrodynamic damping. The importance of considering the hydrodynamic damping and its influence on the mode-shapes of Francis turbines is shown.
CitationValentin, D. [et al.]. Influence of the hydrodynamic damping on the dynamic response of Francis turbine runners. "Journal of fluids and structures", 1 Octubre 2019, vol. 90, núm. October, p. 71-89.