Session: 07-01-05: General Dynamics, Vibration, and Control

Paper Number: 116832

116832 - Foil Gas Bearing Damping Measurements and Analysis With Varied Configurations 

Predictions of bearing damping in turbomachinery are essential to developing reliable, efficient, and safe products. Technology development demands are driving machine designs with increasing power density, which involves increased rotor speeds and structural stresses. The machine designers, therefore, must have a sufficient understanding of bearing damping. Meanwhile, a healthy turbomachinery technology market has development costs that are competitive. The trial-and-error approach is too costly. Analytic solutions are practically non-existent. Numerical solutions and simulations are very limited and experimental data is usually specific to a particular configuration. These challenges for the turbomachinery designer are especially significant when the bearings are of the Foil Gas Bearing (FGB) type. The work completed and represented in this paper intends to serve the turbomachinery designer in their selection and configuration of FGBs, as it makes a connection between the bearing configuration, the applied load level and frequency, and the level of bearing damping they can expect.

To obtain the data required to build a model that captures these relationships, several configurations of foil gas journal bearings are subjected to oscillating loads through the use of an electro-mechanical shaker. Similar to the work of Rubio and San Andres, the bearing displacement and load signals are recorded and analyzed to obtain a coefficient of equivalent viscous damping at frequencies between 20 and 400 Hz and at loads between 2 and 11 lbf. The bearing configuration variations include bump foil thickness, pitch, and height. The data is analyzed and a model developed using a non-linear regression method employing the Gauss-Newton algorithm. The model captures the relationship between an equivalent viscous damping coefficient and a forcing frequency, load, and a non-dimensional geometry configuration parameter G. A thinner bump foil and a closer spacing between bumps (pitch) resulted in higher damping coefficients. For foil gas bearings with a minimized bump-foil thickness, and maximized bump pitch, the increased damping would surely result in higher reliability during operation in this speed range, as long as these parameters are within the limitations set by the designer with more considerations in mind than just maximizing damping.

The results of this work show a strong relationship between this bearing configuration represented by non-dimensional parameter G and the equivalent viscous damping C_e. These results suggest that it is possible to configure a FGB of this type in such a way that its equivalent viscous damping is an order of magnitude greater than other configurations. Such a relationship can be valuable to designers of turbomachinery rotating on FGBs in that it enables them to tailor a bearing configuration to meet the bearing damping requirements of the application, whether that be a higher or lower amount of damping that is desired at that bearing location.

Presenting Author: Chittaranjan Sahay University of Hartford

Presenting Author Biography: Dr. Sahay is a life-time member of ASME. He has actively engaged in research and publications in the areas of Solid Mechanics, Design, Manufacturing, and Metrology for the past 50 years.

Authors:

Jared Knechel University of Hartford
Giri Agrawal R&D Dynamics
Chittaranjan Sahay University of Hartford
Suhash Ghosh Mechanical Engineering, University of Hartford