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Research Papers: Gas Turbines: Structures and Dynamics

Measurements of Rotordynamic Response and Temperatures in a Rotor Supported on Metal Mesh Foil Bearings

[+] Author and Article Information
Thomas Abraham Chirathadam

Research Engineer
Mechanical Engineering Division,
Southwest Research Institute,
San Antonio, TX 78228-0510
e-mail: Thomas.Chirathadam@swri.org

Luis San Andrés

Professor,
Fellow ASME
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843-3123
e-mail: LSanAndres@tamu.edu

DN = Diameter (D) in mm x rotational speed (N) in revolutions per minute.

A safety insulation shield, covering the entire test rig, is assembled during the high temperature measurements for operator safety.

As per ISO 1940 imbalance grade [24].

The rotor response for u = 22.6 μm (me=360 mg) is normalized by multiplying the recorded amplitude x (240 mg/360mg).

In prior tests with two similar bump type foil bearings supporting the rotor [26], a cooling flow rate of ∼160 L/min was found to adequately cool the rotor and the two bearings during high temperature tests, and hence this flow rate is chosen for the current tests. The flow meter is calibrated by the manufacturer at 1 atmosphere and 21 °C. The uncertainty in the measured flow is ±1.5% of the full scale range (500 L/min).

High temperature measurements are conducted only up to a maximum speed of 36 krpm. Ambient temperature measurements are conducted to a maximum speed of 50 krpm.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 24, 2013; final manuscript received July 29, 2013; published online September 23, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(12), 122507 (Sep 23, 2013) (10 pages) Paper No: GTP-13-1176; doi: 10.1115/1.4025237 History: Received June 24, 2013; Revised July 29, 2013

Gas bearings in power generation microturbomachinery (MTM) and for automotive turbocharger applications must demonstrate adequate thermal management without performance degradation while operating in a harsh environment. The paper presents rotor surface temperatures and rotordynamic measurements of a rigid rotor supported on a pair of metal mesh foil bearings (MMFBs) (L = 38.1 mm, D = 36.6 mm). In the tests, to a maximum rotor speed of 50 krpm, an electric cartridge heats the hollow rotor over several hours while a steady inlet air flow rate at ∼160 L/min cools the bearings. In the tests with the heater set to a high temperature (max. 200 °C), the rotor and bearing OD temperatures increase by 70 °C and 25 °C, respectively. Most rotor dynamic responses do not show a marked difference for operation under cold (ambient temperature) or hot rotor conditions. A linear rotordynamics structural model with predicted MMFB force coefficients delivers rotor response amplitudes in agreement with the measured ones for operation with the rotor at ambient temperature. There are marked differences in the peak amplitudes when the rotor crosses its (rigid body) critical speeds. The test bearings provide lesser damping than predictions otherwise indicate. Waterfalls of rotor motion show no sub synchronous whirl frequency motions; the rotor-bearing system being stable for all operating conditions. The measurements demonstrate that MMFBs can survive operation with severe thermal gradients, radial and axial, and with little rotordynamic performance changes when the rotor is either cold or hot. The experimental results, accompanied by acceptable predictions of the bearings dynamic forced performance, promote further MMFBs as an inexpensive reliable technology for MTM.

FIGURES IN THIS ARTICLE
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References

Figures

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Fig. 1

Exploded view of the components in a metal mesh foil bearing

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Fig. 2

Sectioned view of test rotor and bearings inside their housing

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Fig. 3

Close-up view of rotor free end and cartridge heater

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Fig. 4

Finite element structural model of test rotor supported on MMFBs. A flexible coupling connects the drive motor to the connecting rod affixed to the rotor.

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Fig. 5

Predicted damped natural frequency map for rotor-MMFB system. Insets show rotor natural mode shapes for the two lowest forward whirl frequencies.

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Fig. 6

Predicted rotor-bearing system damping ratios corresponding to natural frequencies in Fig. 5

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Fig. 7

Normalized rotor response amplitude and phase angle versus shaft speed for tests with out-of-phase imbalances: 240 mg and 360 mg. Measurements at the rotor DE, horizontal direction during speed ramp up (acceleration 600 rpm/s). Baseline response subtracted.

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Fig. 8

Measured and predicted rotor response amplitude and phase angle versus shaft speed for two out-of-phase imbalance masses (a) 240 mg and (b) 360 mg. Measurements at rotor drive end horizontal direction during rotor speed ramp up. Baseline response subtracted.

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Fig. 9

Locations for measurement of temperatures on the rotor surface and the OD of the bearing cartridges

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Fig. 10

Rotor spinning at 50 krpm: recorded temperature rise on the rotor ends, bearings and inlet duct versus elapsed time. Steady cooling flow into bearings at 160 L/min.

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Fig. 11

Equilibrium temperature rise at rotor OD surface, free and drive ends, versus rotor speed. Steady axial cooling flow into bearings at 160 L/min.

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Fig. 12

Average bearings’ OD temperature rise versus rotor speed and increasing heater temperatures. Steady axial cooling flow into bearings at 160 L/min.

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Fig. 13

Rotor response phase lag and amplitude versus shaft speed for out-of-phase imbalance masses = 240 mg. Measurements at rotor DE (a) horizontal plane and (b) vertical plane. Rotor acceleration = 400 rpm/s. Cooling flow rate ∼160 L/min. Inset table shows average rotor OD temperatures corresponding to each heater set temperature. Baseline response subtracted.

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Fig. 14

Waterfall plot of rotor response amplitudes (DE vertical plane) for (a) heater turned off, and (b) heater set temperature = 200 °C. Rotor acceleration 400 rpm/s. In-phase imbalance masses = 360 mg.

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