Increasing the operating range of Francis turbines by considering dynamic phenomena at part load

Market trends in the hydro industry call for turbines to be much more flexible in terms of their operating range; as a result, an increasing amount of energy is generated at part load and overload operation. In these ‘off-design’ conditions, a wide range of hydraulic phenomena occurs. This paper presents a numerical study of Francis turbines operating at part load, aimed at predicting and optimizing the mechanical response of the turbine, induced by hydraulic pressure fluctuations. First, unsteady CFD calculations were done for a wide range of part-load operating points. The results served as an input for a finite element analysis to model the structural response on the turbine. The methodology was then applied to improve the hydraulic and mechanical design of the turbine for robustness with a broader operating range.