Performance of an Open Ends Squeeze Film Damper Operating with Large Amplitude Orbital Motions: Experimental Analysis and Assessment of the Accuracy of the Linearized Force Coefficients Model



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Squeeze Film Dampers (SFDs) aid to suppress rotor vibrations and enhance the stability of high-speed rotor-bearing systems. A SFD is a simple oil lubricated film between a stationary housing and a precessing (whirling) journal. Aircraft engines use SFDs as the only means to provide damping to otherwise rigid ball bearing supports. This thesis presents experimental results for the dynamic forced performance of a test open ends SFD operating with large amplitude whirl motions, centered and off centered within the bearing clearance. The test rig comprises of an elastically supported bearing with a damper section having two parallel film lands separated by a feed groove. A film land is 25.4 mm long, with diameter 127 mm and nominal radial clearance c=0.251 mm. Two orthogonally placed shakers apply dynamic loads on the bearing to induce circular orbit motions at prescribed whirl frequencies. A static loader, 45? away from each shaker, pulls the bearing to a static eccentric position.

Circular orbit tests were performed (10 ? 100 Hz frequency range) for eight increasing orbit amplitudes (r=0.08c to ~0.71c) and under four static eccentricities (es=0.0c to ~0.76c). An identification method estimates the test damper force coefficients from transfer functions in the frequency domain. The analysis shows that the SFD damping force coefficients increase with the static eccentricity (es) increase. On the other hand, the damper inertia coefficients decrease as the orbit amplitude (r) becomes large and also increase modestly with the static eccentricity (es). Predictions from a physical model show good agreement with the test dynamic force coefficients.

The accuracy of the linearized SFD force coefficients (K, C, M)SFD is evaluated from comparing the differences in mechanical work performed by actual and linear SFD reaction forces. The difference in mechanical work (Ediff) increases with increasing static eccentricity (es) and orbit amplitude (r). However, for most test conditions (r/c?0.4,es/c?0.25), Ediff is less than ~5%, thus showing the linearized SFD force coefficients represent well the forced response of the actual test SFD system.

The test and predicted force coefficients as well as the analysis of the pressure fields contribute to a better understanding of the kinetics of SFDs operating with moderate tolarge amplitude size whirl motions, centered and off-centered.