Experimental and Predicted Rigid Rotor Stability Threshold of Axial Groove and Three-Lobe Bearings

R D Flack,L E Barrett,G J Kostrzewsky

doi:10.1155/s1023621x02000039

R D Flack, L E Barrett + Show 1 more

Open Access

https://doi.org/10.1155/s1023621x02000039

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Abstract

The measured performances of axial groove and preloaded three-lobe journal bearings are compared with the predicted performance. Operating eccentricity and dynamic coecients were found for dierent shaft speeds and various steady loads. Numerical results are based on a Reynolds equation solver, which allows for a variety of thermal eects. Sinusoidal excitations were used to experimentally determine the eight linearized stiness and damping coecients. The rigid rotor stability threshold parameter, vs, and whirl ratio, vd, were found from the dynamic coecients. The experimental and theoretical stability threshold and whirl ratio are correlated as independent functions of both the Sommerfeld number and operating eccentricity. The predicted stability maps are slightly higher than measured, indicating that the predicted characteristics are more stable than measured. The predicted whirl ratios are in approximate agreement with measured values. As expected, the stability maps show the axial groove bearings to be less stable than the preloaded three-lobe bearings.

Highlights

Theoretical predictions are compared to the measured performance of an axial groove and a preloaded three-lobe journal bearing
Measured static operating characteristics and dynamic coecients of an axial groove bearing and a preloaded three-lobe journal bearing were compared to predictions for a range of Sommerfeld numbers
The results provide a designer a moderate level of con®dence in modeling the dynamic stability for Sommerfeld numbers less than about 3.0 for the 3-lobe bearing and 0.2 for the axial groove bearing

Summary

SUMMARY OF PREDICTION METHOD

The theoretical analysis was developed by Branagan (1988) and includes variable viscosity eects in the lubricant ®lm. The linearized coecients were used to ®nd the rigid rotor stability threshold parameter,. ! d the non-dimensional frequency at which the system would vibrate at the instability condition) These two parameters were originally derived by Lund and Saibel (1967) for both rigid andexible rotors supported by bearings with a set of stiness and damping characteristics. The stability parameter is plotted vs the Sommerfeld number and plotted vs the operating eccentricity. The curves on these maps represent the boundary between stable and unstable operation of the bearing with a non- ̄exible rotor. Non-dimensional operating speeds with values larger than the stability parameter will be unstable. All tests that were performed for the data were well into the stable region with speed parameters less than one

Findings

OF RESULTS

SUMMARY