Session: 23-07 Gas Foil Thrust Bearings

Paper Number: 154117

Experimental Investigation of the Influence of Gas Foil Thrust Bearings on the Stability Behaviour of Rotor-Bearing Systems 

Gas foil bearings are a type of aerodynamic bearings which employ compliant foil structures to support rotating machinery, typically at high speeds and low loads. The load bearing lubrication medium is gaseous and in most cases ambient air. This avoids an oil system for bearing lubrication and eliminates the associated risks of oil contamination, for example in air cycle machines or turbo compressors for fuel cells. The frictional contact between the foil surfaces increases bearing damping compared to conventional, rigid gas bearings. However, rotor-bearing systems that involve gas foil bearings are susceptible to sub-synchronous vibration which is caused by a self-excitation of the air film beyond the onset speed of sub-synchronous vibration. This sub-synchronous vibration is often coupled with vibration amplitudes that are larger than the synchronous response. Therefore designers must ensure that a rotor-bearing system operates safely outside of the speed regime of sub-synchronous vibration. This is typically done by numerical stability assessment, however the effects of gas foil thrust bearings are often completely neglected.

While measures have been published to influence the onset speed of sub-synchronous vibration by alteration of various parameters of gas foil journal bearings (radial bearings), no studies have demonstrated the influence of gas foil thrust bearings (axial bearings) on sub-synchronous vibrations. In the experimental work presented herein, the axial clearance of gas foil thrust bearings is adjusted on a test rig in which the rotor is fully supported by gas foil bearings. The effect of the clearance variation is discussed in terms of onset speed of sub-synchronous vibration of the conical rigid body mode, the frequency of vibration and the corresponding vibration amplitudes. The experimental results indicate that gas foil thrust bearings in general, as well as the axial clearance can influence the vibrational behaviour of the rotor-bearings system, thereby leading to the conclusion that, depending on the mode shape of sub-synchronous vibration, thrust bearings must be considered during the stability assessment of the design phase.

Presenting Author: Berk Sorgec Technische Universität Berlin

Presenting Author Biography: Master's degree in mechanical engineering, currently a research assistant at the department of Engineering Design and Product Reliability at Technische Universität Berlin under the lead of Prof. Robert Liebich. Main focus of work is the manufacturing of gas foil bearings for investigative purposes, experimental work considering gas foil thrust bearings and the development and construction of a parameter identification test machine for gas foil thrust bearings.

Authors:

Berk Sorgec Technische Universität Berlin
Robert Liebich Technische Universität Berlin