Effect of Pressurization on the Vibration Isolation Capability of Squeeze Film Bearings

Abstract

This paper investigates theoretically the effect of pressurization on the vibration isolation capability of centrally preloaded squeeze film bearings supporting a rigid rotor which in turn is mounted in rolling element bearings. Assuming the short bearing approximation, constant lubricant properties, and that steady state conditions have been reached with the journal center describing synchronous circular orbits about the bearing center, the theory is developed for the general case of arbitrary pressurization at either end of the bearing. The design data are for bearings pressurized at one end only as in circumferentially grooved bearings and conservatively assume that the saturation vapor pressure of the lubricant is atmospheric. These design curves show the effect of the relevant system parameters on the possibility of undesirable operation modes, on the unbalance force transmissibility and on rotor vibration amplitudes. Hence, the influence of lubricant viscosity, lubricant supply pressure, bearing dimensions, rotor speed, rotor mass, rotor unbalance and support flexibility may be readily determined, allowing for optimal system design. It is shown that significant unbalance force isolation is a practical possibility with consequent decrease in the vibration level of the rotor mounts and increase in rolling element bearing life, while maintaining rotor excursion amplitudes at an acceptable level, even with relatively high unbalance loading. In particular, with increased pressurization, the likelihood of bistable operation can be considerably reduced. The data suggest that by varying the supply pressure and/or the lubricant viscosity, the rotor bearing system may be gainfully controlled to run at minimum vibration level and/or with minimum unbalance transmissibility.