Design of Electromagnetic Dampers for Aero-Engine Applications

The vibration control of rotors for gas or steam turbines is usually performed using passive dampers when hydrodynamic bearings are not used. In layouts where the rotating parts are supported by rolling bearings the damping is usually provided by squeeze film dampers. Their passive nature and the variability of their performances with temperature and frequency represent the main disadvantages. Dampers with magneto-rheological and electro-rheological fluid allow solving only a part of the above mentioned drawbacks. Active magnetic bearings (AMB’s) are promising since they are very effective in controlling the vibration of the rotor and offering the possibility of monitoring the rotor’s behaviour using their displacement sensors. However they show serious drawbacks related to their stiffness. Electromagnetic dampers seem to be a valid alternative to visco-elastic, hydraulic dampers due to, among the others: the absence of all fatigue and tribology issues resulting from the absence of contact; the small sensitivity to the working environment; the wide possibility of tuning even during operation; the predictability of the behaviour; the smaller mass compared to AMB’s and the failsafe capability. The aim of the present paper is to describe a design methodology adopted to develop electromagnetic dampers to be installed in aero-engines. The procedure has been validated using a reduced scale laboratory test rig. The same approach has then been adopted to design the electromagnetic dampers for real civil aircraft engines. Results in terms of achievable vibration reductions, mass and overall dimensions are hence presented. A trade-off between the various proposed solutions has been carried out evaluating quantitative performance parameters together with qualitative aspects that this “more electric” technology implies.