Investigation of the dynamic behaviour of the vertical rotor of a refrigeration compressor supported by foil bearings

This experimental study examines the dynamic behaviour of an innovative refrigeration compressor, whose rotor, operating in a vertical position, is supported by foil bearings. The bearing system eliminates the need for external lubrication and demonstrates a high load capacity and rotational speeds of up to 120,000 rpm. The novelty of this solution lies in the rotor’s vertical orientation, which introduces unique dynamic challenges. Numerical analyses, including modal and forced vibration studies, identified critical frequencies at 181 Hz, 204 Hz, and 283 Hz, closely matching the experimental results, with differences not exceeding 10%. Experimental tests confirmed stable rotor operation within the range of 60,000–120,000 rpm, with vibration amplitudes of the rotor journals not exceeding 0.028 mm in the critical operating range. Furthermore, misalignments in the bearing journals were observed and attributed to variations in lubrication clearance and foil deflections. The findings demonstrate the feasibility of foil bearings in vertically oriented high-speed compressors and provide novel insights into their dynamic behaviour. During the experimental study, irregular multi-loop vibration trajectories of the bearing journals were observed, necessitating the use of the differential method to determine their direction. This study advances oil-free compressor technology and offers guidance for future design and optimisation.