Dynamics of a misaligned Kaplan turbine with blade-to-stator contacts

• The global dynamics of bladed rotors can be scaled with the number of blades.
• The contact stiffness has a major role in the dynamics of bladed systems.
• Increasing damping at the runner position will stabilize the motion.
• The simple contact modeling allows us to perform fast simulations for real systems.

Rotor-to-stator contacts can occur in hydropower systems due to mechanical and electrical misalignment as well as high unbalance forces. It can result in high impact forces and damages in case of malfunction of the machine. As a result, a real hydropower rotor is studied to evaluate the different types of dynamic motion due to multiple impacts when it is initially misaligned. In this paper, the simplicity of its blade rubbing modelling allows us to evaluate in a fast and efficient way the dynamics of this system as a function of several design parameters. It is observed that the global dynamics of the system are similar to simple bladed Jeffcott rotors when scaled with the number of blades. Since the rotor runs at its operating point, the contact forces are also evaluated at nominal speed. A parametric study – as a function of contact stiffness and damping – is performed and results are given in terms of Poincaré sections, bifurcation diagrams and maximum displacements at steady state. These simulations are used to determine if the system is safe to operate. It can be used to design hydropower rotors by choosing the operating speed in a suitable range, or to analyse if the machine can be stopped before a catastrophe occurs.