Abstract

This paper focuses on the calculation of eigenfrequencies and mode shapes of radial inflow turbines by means of FEM. In a first step investigations have been performed on a single blade model using different boundary conditions. The results have been compared to calculations with the entire rotor. A cyclic and an anticyclic boundary condition has been found which are suitable to model mode shapes with zero nodal diameters and mode shapes with the highest possible number of nodal diameters respectively. In a second step the mode shapes of the single blades of the entire rotor are investigated and compared with each other. Depending on the mode shape of the rotor the mode shapes of the blades are equal or differ slightly from each other. Knowing the exact mode shapes of the single blades of the entire rotor is important for the instrumentation of the rotor with strain gauges in order to perform vibration measurements. The variation of the mode shapes of the single blades has to be taken into account if stress distribution in the entire rotor will be calculated using the measured strains as a basis.