A new vortex preventing element design for francis turbines and ınvestigation of turbine performance

In this study, a new design is made to prevent vortex rope phenomena which may be occur due to instant pressure fluctuations at the draft tube of Francis turbines. In this study, Computational Fluid Dynamics (CFD) analyses are used to obtain the turbine performance and the data is verified with experimental results extracted from a previous study. Stage number of Vortex Preventing Element, the height of Vortex Preventing Element and guide vanes angle of Francis turbine is selected as factors to carry out an optimization study. Box-Behnken experimental design is selected due to lower experiment number and the non-linear relationship between the specified parameters. Optimization and CFD studies are carried out simultaneously and as a consequence, a regression equation is obtained. Accordingly, the most effective parameter on turbine performance is observed as guide vanes angle, and the second one is the relation between guide vanes angle and stage number of Vortex Preventing Element. Besides, if the single-staged Vortex Preventing Element is used in Francis turbine design, it is seen that the component shreds the vortex rope through the draft tube wall. Also, the VPE forges an %1 additional increment on turbine efficiency.