Asynchronous dynamic coefficients of a three lobe air bearing

The study of dynamic whirl behavior of air bearings is fundamental for an adequate rotordynamic analysis and future validation of numerical predictions. This work shows the dynamic response of the air film on a three lobe bearing under non-synchronous whirl motion. One-dimensional multifrequency orbits are used to characterize the bearing rotordynamic coefficients. The test rig uses two magnetic bearing actuators to impose any given orbits to the journal. The dynamic forces are measured on the test bearing housing by three load cells. Journal whirling excitation is independent of the rotating speed, thus allowing asynchronous excitations. The multi frequency excitation is applied at each rotating speed up to 11000rpm allowing the non-synchronous characterization of the air film. The experimental procedure requires two linearly independent excitation sets. Thus, vertical and horizontal onedimensional multi-frequency orbits are applied as perturbations. Results show the synchronous and asynchronous dynamic coefficients of the air bearing. Asynchronous experimental results are compared to numerical estimation of the bearing force coefficients through solution of the isotropic ideal gas journal bearing Reynolds equation. Numerical dynamic coefficients are obtained as the effective coefficient values of the bearing when subject to a given orbit. A full characterization of the non-synchronous rotordynamics coefficients of the bearing is presented in three dimensional maps.