Simplified model of the turbine runner blade

Francis turbine blade is modelled by circular beams loaded by uniformly distributed pressure. This simplification allows for analytical calculations of maximum stresses followed by comparisons with FEM analysis for the same turbine. Two beam models have been proposed and one of them showed good correlation with FEM for different operation conditions. This model has been applied to analyse the operation data recorded during the whole time of operation of the Unit 2 of Derbendikan hydropower station. The results show evolution of the maximum tensile stresses, which makes clear that the appearance of cracks in turbine blades cannot be explained by the high stresses level alone but by combination of different factors.