Extended Abstract

Extended Abstract

Squeeze Film Dampers (SFDs) are commonly used to effectively enhance the damping force to the rotating shaft supported by rolling element bearings. Thus, the dynamic behavior of such a rotor system depends strongly upon the dynamic characteristics of the SFD in service. In the past, many researchers put much effort in either experimental determination or analytical prediction of the dynamic properties of SFD in service. However, few research results are found completely satisfactory yet, due to the complexity of the SFD analysis and the difficulty in experimentations.

Squeeze film dampers (SFDs) are essential components of high-speed turbomachinery since they offer the unique advantages of dissipation of vibration energy and isolation of structural components, as well as the capability to improve the dynamic stability characteristics of inherently unstable rotor-bearing systems. SFDs are used primarily in aircraft jet engines to provide viscous damping to rolling element bearings which themselves have little or no damping. One other important application is related to high performance compressor units where SFDs are installed in series with tilting pad bearings to reduce (soften) bearing support stiffness while providing additional damping as a safety mechanism to prevent rotordynamic instabilities.

In spite of the many successful applications, industry often recognizes that the design of SFDs is based on overly simplified theoretical models that either fail to incorporate or simply neglect unique features (structural and fluidic) that affect the damper dynamic force performance. Actual damper performance can range from erratic to non-functioning depending on the operating conditions. The lack of adequate understanding of the mechanics of squeeze film flows is essentially due to the near absence of fundamental experimental evidence and sound rationale that directly addresses the issues and problems of interest.

The earliest application of a SFD in an industrial machine is credited to Sir Charles Parsons who invented in 1889 the radial flow steam turbine; 32 kW in size and running at 6,000 rpm. Arthur Bill from Rolls Royce, Ltd. claimed the first patent describing a SFD. The specification stated an advantageous means of damping vibrations in bearings is to provide a hydrodynamic fluid film, sometimes referred to as a "squeeze film” between the bearing and its supporting structure. One of the specific embodiments of the invention was described as an application to axial flow compressor bearings as used in aircraft engines.


A squeeze film damper (SFD) consists of an inner non-rotating journal and a stationary outer bearing, both of nearly identical diameters. Figure 1 shows an idealized schematic of this type of fluid film bearing. A journal is mounted on the external race of a rolling element bearing and prevented from spinning with loose pins or a squirrel cage that provides a centering elastic mechanism. The annular thin film, typically less than 0.250 mm, between the journal and housing is filled with a lubricant provided as a splash from the rolling bearing elements lubrication system or by a dedicated pressurized delivery. In operation, as the journal moves due to dynamic forces acting on the system, the fluid is displaced to accommodate these motions. As a result, hydrodynamic squeeze film pressures exert reaction forces on the journal and provide for a mechanism to attenuate transmitted forces and to reduce the rotor amplitude of motion.