Computation of stress distribution in a Francis turbine runner induced by fluid flow

Abstract

In this paper the hydraulic stresses induced in a Francis turbine runner blade by steady fluid flow were investigated. Based on the one-way coupled simulation, the approach consists of a fluid flow analysis which provides the distribution of the fluid pressure on the blade, followed by the structural finite element analysis. The three dimensional turbulent flow in both distributor and runner of Francis turbines were computed. The computational domains correspond to interblade channels for the Francis turbine distributor and runner, respectively. In order to couple the steady absolute distributor flow field with the runner steady relative flow, a mixing interface technique is used on the conical distributor–runner interface. The hydrodynamic field is computed in seven operating points at constant head from part load to full load conditions. The pressure coefficient distribution on the blade is plotted in order to evaluate the blade loading and region with cavitational risk. Further, the stress distributions were obtained by a structural finite element analysis performed for the steady loading in order to determine the areas with highest stress values.