Simulation of Blank Design for Blades of Francis Turbines

The metal pressing process which is widely used in many industries has advantages over casting process for producing large and thick blades of Francis turbine. For the design of pressing process, blank design should be firstly performed to determine the dimension of the flat blank. In fact, the traditional trial and error approach is not applicable for the blade design for Francis turbines that is not standard because of the different hydraulic characteristics of a hydropower plant from site to site. The powerful computing technology makes it possible to desgn optimum blanks by numerical modeling and simulation. In this paper, the multi-step inverse finite element approach is investigated for blank design and an elasto-plastic model has been built by using the well-known software ANSYS. Unfolding tests with cylindrical sections have been carried out and the numerical results agree well with the analytical results. Thereafter, a large and thick blade of Francis turbine for hydropower plants has been successfully unfolded by the FE model. Finally, for ensuring the machining of the blade after the pressing process, a new contour is obtained by extending the boundary of the flat blank provided by the FE model.