Experimental prediciton of instability in rotor seal systems using output only data

In common high-speed turbomachinery or pumps, usually contactless seals are used to separate different fluids and Pressure levels. The seal gap causes a fluid flow, which generates rotational speed dependent forces to the rotor in the deflectional and tangential directions. They act like cross-coupled stiffness and can excite the rotor system to large vibrations, the instability occurs similar to the ‘oil whip’ phenomenon in journal bearings. Thus, a diagnosis method is necessary to ensure safe operation. To predict the speed limit of the machinery, two methods are presented in this research: an analysis using active magnetic bearing excitation and an output only damping ratio estimation method. The methods are experimentally evaluated on a test rig and using numerical simulations.