Presentation on theme: "Mast-Childs Professor Principal Investigator"— Presentation transcript:
1 Mast-Childs Professor Principal Investigator 28th Turbomachinery Consortium MeetingDynamic Forced Response of a Rotor-Hybrid Gas Bearing System due to Intermittent ShocksLuis San AndrésMast-Childs ProfessorPrincipal InvestigatorKeun RyuResearch AssistantTRC-B&C-1-082008 TRC ProjectGAS BEARINGS FOR OIL-FREE TURBOMACHINERY
2 Gas bearings Micro Turbomachinery (< 0.5 MW) ADVANTAGES ASME Paper No. GTADVANTAGESHigh energy densityCompact and fewer partsPortable and easily sizedLower pollutant emissionsLow operation costOil-Free bearingHigh rotating speed (DN value>4M)Simple configurationLower friction and power lossesCompact sizeGas bearingsAIAAGas Foil BearingGTFlexure pivot Bearing
3 Gas Bearings for MTM Gas bearings for micro turbomachinery (< 0.5 MW ) must be:Simple – low cost, small geometry, low part count, constructedfrom common materials, manufactured with elementary methods.Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system.High Rotor Speeds – no specific speed limit (such as DN) restricting shaft sizes. Small Power losses.Good Dynamic Properties – predictable and repeatable stiffness and damping over a wide temperature range.Reliable – capable of operation without significant wear or required maintenance, able to tolerate extended storage and handling without performance degradation.+++ Modeling/Analysis (anchored to test data) readily available
4 Gas Bearings for MTM Thrust in TRC program: Investigate conventional bearings of low cost, easy to manufacture (common materials) and easy to install & align.Combine hybrid (hydrostatic/hydrodynamic) bearings with low cost coating to allow for rub-free operation at start up and shut downMajor issues:Little damping, Wear at start & stop,Instability (whirl & hammer), & reliability under shock operation
5 Gas bearing test rig Max. operating speed: 100 kpm 3.5 kW (5 Hp) AC integral motorRotor: length 190 mm, 28.6 mm diameter, weight=0.826 kgRig housingBearing shell andLoad cellsGas bearingBearing coverShaft and DC motorComponents of high-speed gas bearing test rig
6 2007: Control of bearing stiffness / critical speed Gas Bearings for MTMGT2007: Control of bearing stiffness / critical speedDisplacements at RB(H)5.08 bar2.36 bar5.08 barBlue line: Coast down2.36 barRed line: Set speedController activated systemPeak motion at “critical speed” eliminated by controlling supply pressure into bearings
7 ObjectivesDemonstrate the rotordynamic performance, reliability, and durability of hybrid gas bearingsRotor motion measurements for increasing gas feed pressures and speed range to 60 krpm.Install electromagnetic pusher to deliver impact loads into test rig.Perform shock loads (e-pusher & lift-drop) tests to assess reliability of gas bearings to withstand intermittent shocks without damage.
8 TEST gas bearings TEST gas Bearings worn pads surfaces Flexure Pivot Hybrid Bearings: Promote stability, eliminate pivot wear, engineered product with many commercial applicationsworn pads surfacesClearances Cp =38 & 45 mm, Preload =7 & 5 mm (~20%)Web rotational stiffness=20 Nm/rad
9 2008 Gas Bearing test rig layout E-pusher: Push type solenoid240 Nat 1 inch stroke
11 Manual lift & drop tests Multiple impactLift off to 5~15 cm (10~30° rotation)
12 Coast down: E-pusher tests Ps=5.08 bar (ab)Displacements at LB(H)Intermittent shocksImpact force 100~400 N46 krpmShock ~15 gTransient rotor response ~ 40 µm
13 Coast down: manual lift & drop tests Shock induced accelerationAt base 5~20 gAt housing 5~10 gPs=3.72 bar (ab)Beyond critical speed: Synchronous frequency is isolated from shocksBelow 20 krpm:Large fluctuation of synchronous responseDisplacements at LB(H)
14 Waterfall: manual lift & drop tests Displacements at LB(H)Ps=2.36 bar (ab)Rotor speeddecreasesExcitation of rotor natural frequency. NOT a rotordynamic instability!
15 Rotor response: manual lift & drop tests Ps=2.36 bar (ab)Shock loads appliedShock loads appliedOverall rotor amplitude increases largely. Subsynchronous amplitudes larger than synchronous
16 Rotor response: manual lift & drop tests Ps=2.36 bar (ab)Natural frequency of rotor-bearing system (150~190 Hz)Natural frequency of test rig (~40 Hz)Rotor-bearing natural frequency increases with rotor speed. Natural frequency of test rig also excited.
17 Rotor response: manual lift & drop tests Ps=2.36 bar (ab)15 krpmDrop induced shocks ~30 gTransient responseFull recovery within ~ 0.1 sec.
18 Rotor speed vs time (No shocks) Dry friction(contact)With feed pressure: long time to coast down demonstrates very low viscous drag!
19 Rotor speed vs time (Manual lift-drop tests) Overall coast down time reduces with shock loads (~ 20 sec)No shocksExponential decay (No rubs) even under severe external shocksNo shocks
20 ConclusionsUnder shock loads ( up to ~30 g), natural frequency of rotor-bearing system ( Hz) and test rig base (~ 40 Hz) excited. However, rotor transient motions quickly die!For all feed pressures (2-5 bar), rotor transient responses from shocks restore to their before impact amplitude within 0.1 second. Peak instant amplitudes (do not exceed ~50 µm)Even under shock impacts, viscous drag effects are dominant, i.e., no contact between the rotor and bearing.Hybrid bearings demonstrate reliable dynamic performance even with WORN PAD SURFACES
21 TRC Proposal: Gas Bearings for Oil-Free Turbo-machinery – Identification of Bearing Force Coefficients from Base-Induced ExcitationsTASKSSet up an electromagnetic shaker to deliver excitations (periodic loads of varying frequency) to the test rig.Measure the rotor response due to base induced excitations.Identify frequency dependent bearing stiffness and damping coefficients from measured rotor transient responses at increasing rotor speeds.Compare the identified bearing force coefficients to predictions from XLTRC2 computational models.BUDGET FROMTRCFOR2008/2009:Support for graduate student (20h/week) x $ 1,600 x 12 months,Fringe benefits (2.5%) and medical insurance ($194/month)$ 22,008Tuition & fees three semesters ($3,996x3) + Supplies for test rig$ 17,992Total Cost:$ 40,000
22 Electromagnetic shaker Shaker force peak amplitude (sine): 98 N (22 lbf)Useful frequency range: 5 ~ 9000 HzLDS V406/8 – PA 100EOperating rotor speed range: 170 Hz ~ 1 kHz10 krpm ~ 60 krpmYXLow frequency excitations: simulate roadsurface effect on MTMZIdentify frequency dependent bearing force coefficients at increasing rotor speeds
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