1 Identification of structural stiffness and material loss factor in a shimmed (generation one) bump type foil bearing Luis San Andrs Mast-Childs Professor May 2013 Joshua Norsworthy Graduate Research Assistant TRC-B&C rd Turbomachinery Research Consortium Meeting TRC Project 32513/1519 FB Metal Mesh Foil Bearings: Operation at high temperatures 2 Bump-type foil bearing (BFB) BFB components: bearing cartridge, bump Foil strip (compliant), and top foil Hydrodynamic air film pressure develops between the rotating shaft and the top foil Bearing Cartridge Top Foil Bump Foil Top Foil Fixed End Bump Foil Applications: ACMs, micro gas turbines, turbo expanders, turbo compressors, turbo blowers, soon in automotive turbochargers Adequate load capacity provided by the bump foil strip (compliant) Frictional damping (due to relative motion of bump foils) dominates Tolerant to misalignment Bearing Cartridge Issues with foil bearings Endurance: performance at start up & shut down Little test data for rotordynamic force coefficients Thermal management for high temperature applications (gas turbines, turbochargers) Prone to subsynchronous whirl and limit cycle operation RudDloff, L., Arghir, M., et al., 2011, Experimental Analysis of a First generation foil Bearing. Start-Up Torque and Dynamic Coefficients, ASME GT Unloaded FB: Self-Excited whirl motions at speed 30 krpm (500 Hz) with whirl frequency=165 Hz (WFR=0.33) Example s ubsynchronous motions 5 Original GFB Shimmed GFB Original GFB Inserting metal shims underneath bump strips introduces a preload (centering stiffness) at low cost typical industrial practice. Preload produces centering stiffness at small loads Original and shimmed GFBs Kim, T.H., and San Andrs, L., 2009, Trib. Trans. Test BFB specifications L DoDo DiDi 2c nom ParametersMagnitude Bearing cartridge outer diameter, D O mm Bearing cartridge inner diameter, D I mm Bearing axial length, L38.10 mm Top foil thickness (Inconel X750), t T 0.1 mm foil length, 2D I 110 mm Number of bumps, N B 26 Bump foil (Inconel X750) Thickness, t B mm Pitch, s mm Length, l B 2.1 mm Height, h B 0.50 mm Shim (AISI 4140) length Length 38.1 mm Thickness, t s 50 m Width7.87 mm Angular extent11.8 Shaft diameter, D s 36.5 mm Measured inner diameter of the FB (assembled) mm Nominal FB radial clearance, c nom =(D I -D s )/ mm Weight of test bearing and outer cartridge1.1 kg (10 N) L/D = 1.03 7 Top Foil Bump Foil Metal Shim Bearing Cartridge Shimmed bump-type foil bearings Shimmed bumps are pressed closer to the rotor than other bumps Shims are added at discrete locations circumferentially and stretch axially The shims have an adhesive glue layer on the bottom 8 Clearance in a shimmed BFB Clearance profile: c nom : Nominal bearing clearance t S : Shim thickness N S : Number of shims : Angular coordinate p : Angular distance between consecutive shims 1 : Angular coordinate of the first shim (all angular coordinates taken from the middle of the shim) Eddy current sensor Lathe saddle Test bearing Shaft affixed in lathe chuck Load cell Lathe chuck Lathe tool holder Eddy Current sensor Load cell Test bearing Stationary shaft Lathe chuck holds shaft & bearing during loading/unloading cycles. Static load test rig Dr. Chirathadam, TRC 31 st (2011) 10 Load-deflection results for original BFB Region of bump compression Bearing reaction force: Regions of low load (