Magnetic Excitation of a Three-Bearing Rotor

Exciting mechanisms, such as the flow induced clearance or aerodynamic excitation and the hydrodynamic bearing excitation cause self-excited vibrations of the turbomachinery rotor. By a magnetic simulation of the flow-induced nonconservative forces, the stability behavior and stabilizing measures can be investigated, on the bases of arbitrary rotor configurations. The magnetic bearing is used to excite a three-bearing rotor. The natural frequencies are varried by the direct stiffness of the magnetic bearing. Stiffening of the shaft does not stabilize the multi-bearing rotor generally. When the magnetic excitation • counteracts the journal bearing excitation, the stability of the rotor is improved for the first and the second vibration mode. The experimental results are compared to theoretical results obtained by finite element calculation.