Influence of Ambient Pressure on Measured Stiffness and Damping of Radial Gas Foil Bearings

As gas bearings have gained popularity, they have been used in a diverse range of applications. In many cases these bearings are used in various process gases at a range of pressures. Although numerous analytical tools exist to predict the behavior of gas bearings in these environments, these tools are challenging to validate. The current work describes a test loop that is capable of measuring rotordynamic force coefficients in a hermetically sealed environment. To the author's knowledge, this capability is the first of its kind. To illustrate operation of the test rig, an industrial 3-lobe gas-foil bearing was installed in the test fixture, and operated at pressures from 0.5 to 3.5 bar(a) at speeds ranging from 25 to 65 krpm. The tests show that dynamic coefficients increase with speed and pressure; however, a slight reduction in coefficients were observed at the highest speed under ambient conditions. In addition, subambient pressure tests showed higher than ambient stiffness, but comparably low damping in comparison to the other test cases. It is believed that this is the first publication of gas foil bearing coefficients at subambient pressure.