A large portion of the hydraulic power plants in Sweden have axially cooled generators, with axial fan blades that have a risk of failure due to flow-induced vibrations. During refurbishment there is a chance to decrease the risk of failure with a better knowledge of the flow-induced forces and their interaction with the fan blades.
The forces are likely to increase under some of the conditions when the generator is speeding up to the operating condition, or when it is shutting down. Such operating procedures will increase with a more flexible operation of hydraulic power plants. There is a great lack of knowledge in this field.
In order to prevent this kind of problems a frequency analysis of the fan blades is carried out during the design phase. It is very important that the flow-induced frequencies of the forces acting on the fan blades, due to e.g. vortex separation, do not coincide with the eigen frequency of the blades. That requires a detailed understanding of the flow around fan blades with designs particularly used in axially cooled hydro power generators.
The studies will be performed by using CFD with highly resolved Large-Eddy Simulation (LES) turbulence modeling which is the most suitable technique for detailed studies of vortex separation and other unsteady behavior.