Foil Gas Bearing With Compression Springs: Analyses and Experiments

A new foil gas bearing with spring bumps was constructed, analyzed, and tested. The new foil gas bearing uses a series of compression springs as compliant underlying structures instead of corrugated bump foils. Experiments on the stiffness of spring bumps show an excellent agreement with an analytical model developed for the spring bumps. Load capacity was measured to demonstrate the feasibility of the new foil bearing. Constructed bearing showed a load capacity of 96N at 20,000rpm under no cooling. Measured temperature rise for cooled bearing (with cooling air flow rate of 1350 cm3/sec) was less than 15°C up to 96N, indicating very effective cooling performance of the designed cooling jacket and a possibility of large margin of load capacity beyond the 96N. Initial selection of spring geometry rendered rather soft supports compared to other bump foil bearings, and thus allowed only limited loads during the test. Measured structural stiffness and damping evidence the existence of necessary damping for stable bearing operations. Structural stiffness was highly nonlinear and showed different behaviors between the static loading and sinusoidal dynamic loading. Under the small sinusoidal loadings, presumable stick slip at the interface between spring bumps and bearing sleeve rendered rather high bump stiffness close to the clamped-end case. The measured equivalent viscous damping coefficients increased with applied load amplitudes. The orbits and coast down simulations using the calculated stiffness and measured structural loss factor indicate that the damping of underlying structure can suppress the maximum peak at the critical speed very effectively but not the hydrodynamic rotor-bearing instability. The orbit simulations also show the foil gas bearings can accommodate large rotor excursion at speeds beyond the onset speed of instability.