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Gas Bearings for Oil-Free Turbomachinery 28th Turbomachinery Consortium Meeting Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System due to Intermittent.

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Presentation on theme: "Gas Bearings for Oil-Free Turbomachinery 28th Turbomachinery Consortium Meeting Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System due to Intermittent."— Presentation transcript:

1 Gas Bearings for Oil-Free Turbomachinery 28th Turbomachinery Consortium Meeting Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System due to Intermittent Shocks TRC-B&C TRC Project GAS BEARINGS FOR OIL-FREE TURBOMACHINERY Keun Ryu Research Assistant Luis San Andrés Mast-Childs Professor Principal Investigator

2 Gas Bearings for Oil-Free Turbomachinery Micro Turbomachinery (< 0.5 MW) High energy density Compact and fewer parts Portable and easily sized Lower pollutant emissions Low operation cost ADVANTAGES Oil-Free bearing High rotating speed (DN value>4M) Simple configuration Lower friction and power losses Compact size Gas bearings AIAA Gas Foil Bearing GT Flexure pivot Bearing ASME Paper No. GT /Oilfree/turbocharger.htm

3 Gas Bearings for Oil-Free Turbomachinery Gas bearings for micro turbomachinery (< 0.5 MW ) must be: Simple – low cost, small geometry, low part count, constructed from 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 Gas Bearings for MTM

4 Gas Bearings for Oil-Free Turbomachinery 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 down Major issues: Little damping, Wear at start & stop, Instability (whirl & hammer), & reliability under shock operation Gas Bearings for MTM

5 Gas Bearings for Oil-Free Turbomachinery Max. operating speed: 100 kpm 3.5 kW (5 Hp) AC integral motor Rotor: length 190 mm, 28.6 mm diameter, weight=0.826 kg Components of high-speed gas bearing test rig Rig housing Bearing shell and Load cells Gas bearing Bearing cover Shaft and DC motor Gas bearing test rig

6 Gas Bearings for Oil-Free Turbomachinery 2007: Control of bearing stiffness / critical speed Peak motion at critical speed eliminated by controlling supply pressure into bearings Controller activated system Displacements at RB(H) 5.08 bar 2.36 bar Blue line: Coast down Red line: Set speed 2.36 bar 5.08 bar Gas Bearings for MTM GT

7 Gas Bearings for Oil-Free Turbomachinery Demonstrate the rotordynamic performance, reliability, and durability of hybrid gas bearings Rotor 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 Objectives

8 Gas Bearings for Oil-Free Turbomachinery Clearances Cp =38 & 45 m, Preload =7 & 5 m (~20%) Web rotational stiffness=20 Nm/rad TEST gas bearings worn pads surfaces Flexure Pivot Hybrid Bearings: Promote stability, eliminate pivot wear, engineered product with many commercial applications TEST gas Bearings

9 Gas Bearings for Oil-Free Turbomachinery E-pusher : Push type solenoid 240 N at 1 inch stroke 2008 Gas Bearing test rig layout

10 Gas Bearings for Oil-Free Turbomachinery Electromagnetic pusher tests Impact duration ~20 ms E-force ~400 N (pk-pk) Multiple impact

11 Gas Bearings for Oil-Free Turbomachinery Manual lift & drop tests Multiple impact Lift off to 5~15 cm (10~30° rotation)

12 Gas Bearings for Oil-Free Turbomachinery Shock ~15 g Transient rotor response ~ 40 µm 46 krpm Intermittent shocks Impact force 100~400 N Displacements at LB(H) Ps=5.08 bar (ab) Coast down: E-pusher tests

13 Gas Bearings for Oil-Free Turbomachinery Shock induced acceleration At base 5~20 g At housing 5~10 g Beyond critical speed: Synchronous frequency is isolated from shocks Below 20 krpm: Large fluctuation of synchronous response Ps=3.72 bar (ab) Displacements at LB(H) Coast down: manual lift & drop tests

14 Gas Bearings for Oil-Free Turbomachinery Rotor speed decreases Excitation of rotor natural frequency. NOT a rotordynamic instability! Ps=2.36 bar (ab) Displacements at LB(H) Waterfall: manual lift & drop tests

15 Gas Bearings for Oil-Free Turbomachinery Overall rotor amplitude increases largely. Subsynchronous amplitudes larger than synchronous Rotor response: manual lift & drop tests Ps=2.36 bar (ab) Shock loads applied

16 Gas Bearings for Oil-Free Turbomachinery 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. Rotor response: manual lift & drop tests Ps=2.36 bar (ab)

17 Gas Bearings for Oil-Free Turbomachinery Rotor response: manual lift & drop tests 15 krpm Drop induced shocks ~30 g Transient response Full recovery within ~ 0.1 sec. Ps=2.36 bar (ab)

18 Gas Bearings for Oil-Free Turbomachinery With feed pressure: long time to coast down demonstrates very low viscous drag! Dry friction (contact) Rotor speed vs time ( No shocks )

19 Gas Bearings for Oil-Free Turbomachinery Overall coast down time reduces with shock loads (~ 20 sec) Exponential decay (No rubs) even under severe external shocks Rotor speed vs time (Manual lift-drop tests) No shocks

20 Gas Bearings for Oil-Free Turbomachinery Under 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 Conclusions

21 Gas Bearings for Oil-Free Turbomachinery TRC Proposal: Gas Bearings for Oil-Free Turbo- machinery – Identification of Bearing Force Coefficients from Base-Induced Excitations Set 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 XLTRC 2 computational models. TASKS B UDGET FROM TRC FOR 2008/2009 : Support for graduate student (20h/week) x $ 1,600 x 12 months, Fringe benefits (2.5%) and medical insurance ($194/month) $ 22,008 Tuition & fees three semesters ($3,996x3) + Supplies for test rig $ 17,992 Total Cost: $ 40,000

22 Gas Bearings for Oil-Free Turbomachinery Electromagnetic shaker Shaker force peak amplitude (sine): 98 N (22 lbf) Useful frequency range: 5 ~ 9000 Hz Identify frequency dependent bearing force coefficients at increasing rotor speeds Operating rotor speed range: 170 Hz ~ 1 kHz 10 krpm ~ 60 krpm Z X Y LDS V406/8 – PA 100E Low frequency excitations: simulate road surface effect on MTM


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