Abstract
Power density and process lubrication represent two key challenges in turbomachinery systems, guided by the pursuit of cleaner and more sustainable energy requirements. Novel developments in gas bearing technologies allow for improvements in both of these areas. One such development is the use of porous carbon as a delivery mechanism for hydrostatic lubrication in bearings due to its ability to create an even distribution of gas, effectively increasing bearing load capacity. Utilizing porous carbon in a compliantly damped hybrid gas bearing (CHGB) also allows preventing catastrophic failure in the event of intermittent contact, rubbing, or loss of air pressurization, due to the high lubricity of graphite and low friction surface. The use of a compliant bearing support structure allows the bearing to accommodate misalignment, centrifugal growth, large rotor excursion, and develop larger damping forces by integrating an external damper which works in series with the gas film. A MW-class turboexpander rotor is used as a reference point in the design of compliant bearing support structures with specific radial, angular, and transverse stiffness properties. This paper presents the design of a compliant bearing structure coupled to a porous carbon mechanical mate, test rig, and experimental results for non-rotating dynamic characterization tests. Non-rotating uniaxial tests are performed as part of the dynamic characterization of a single compliantly mounted pad and external damper, with excitation frequencies ranging between 30 and 500 Hz. Static loading tests show that the compliant supports dominate the stiffness of the system. Mechanically preloading the pad through external loading results in an increased equivalent stiffness and improves the stiffness ratio between the gas film and the pad support. The external damper develops high damping levels at low frequencies, which indicates good transmissibility between the pad structure and damper. Experimental data shows promising results for using this design in MW-class rotor applications, with frequency dependent behavior and damping entitlement as the primary hurdles to achieving system level operation.
