Research Papers: Gas Turbines: Structures and Dynamics

Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System—Part I: Measurements

[+] Author and Article Information
Luis San Andrés, Keun Ryu

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843

Tae Ho Kim1

Energy Mechanics Research Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, Seoul 136-791, Korea

The coupling force is not considered for the static load distribution.

The authors recognize the need for an appropriate coating (solid lubricant) to reduce the startup friction and to promote an early lift-off rotor speed. A tight project budget dictated the acquisition of the uncoated bearings.

Note that the displacement peak amplitude is not evident (multiple peaks as well as a too broad band due to high damping) to identify a true system critical speed.

The maximum operating temperature of the cartridge heater (rated at 400 W with 120Vac) is 360°C, while the rotor operates at a speed of 30 krpm and with no cooling flow into the test bearings.


Conducted work as a Post-Doctoral Research Associate at Texas A&M University.

J. Eng. Gas Turbines Power 133(6), 062501 (Feb 17, 2011) (10 pages) doi:10.1115/1.4001826 History: Received April 09, 2010; Revised April 15, 2010; Published February 17, 2011; Online February 17, 2011

Implementation of gas foil bearings (GFBs) into micro gas turbines requires careful thermal management with accurate measurements verifying model predictions. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot (157°C maximum rotor outer diameter (OD) temperature). Part I details the test rig and measurements of bearing temperatures and rotor dynamic motions obtained in a hollow rotor supported on a pair of second generation GFBs, each consisting of a single top foil (38.14 mm inner diameter) uncoated for high temperature operation and five bump strip support layers. An electric cartridge (maximum of 360°C) loosely installed inside the rotor (1.065 kg, 38.07 mm OD, and 4.8 mm thick) is a heat source warming the rotor-bearing system. While coasting down from 30 krpm to rest, large elapsed times (50–70 s) demonstrate rotor airborne operation, near friction free, and while traversing the system critical speed at 13krpm, the rotor peak motion amplitude decreases as the system temperature increases. In tests conducted at a fixed rotor speed of 30 krpm, while the shaft heats, a cooling gas stream of increasing strength is set to manage the temperatures in the bearings and rotor. The effect of the cooling flow, if turbulent in character, is most distinctive at the highest heater temperature. For operation at a lower heater temperature condition, however, the cooling flow stream demonstrates a very limited effectiveness. The measurements demonstrate the reliable performance of the rotor-GFB system when operating hot. The test results, along with full disclosure on the materials and geometry of the test bearings and rotor, serve to benchmark a predictive tool. A companion paper (Part II) compares the measured bearing temperatures and the rotor response amplitudes to predictions.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 6

Test condition 1: Effect of shaft temperature on rotor response. Rotor amplitude and lag phase angle of synchronous response for tests at four heater reference temperatures (Ths). No axial cooling flow into bearings. Rotor drive end, horizontal plane (DH).

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Figure 7

Test condition 1: Waterfalls of rotor coastdown response from 30 krpm. Rotor drive end, horizontal plane (DH). Tests with (a) heater off and (b) with cartridge heater on at Ths=360°C. No axial cooling flow into bearings.

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Figure 8

Test condition 1: Effect of shaft temperature on time extent for speed coastdown. Tests with increasing heater temperatures and without forced cooling flow.

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Figure 12

Test conditions 2 and 3: Effect of cooling flow rate on elapsed time for rotor speed coastdown. Operation with heater reference temperature (Ths) at 360°C.

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Figure 13

Surface condition of test GFBs (negative photographs) and rotor before and after high temperature rotordynamic tests

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Figure 14

Rotor OD surface temperature versus axial location for increasing heater temperature (Ths). Ambient temperature at 21°C.

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Figure 15

Test condition 1: Steady state temperature rises in rotor surface at FE (T11) and DE (T12) locations and FE (T1) and DE (T6) bearing cartridges versus heater reference temperature (Ths). Rotor speed of 30 krpm. No axial cooling flow into bearings.

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Figure 1

Photograph of high temperature GFB rotordynamic test rig

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Figure 2

Schematic view (not to scale) for dimensions of test rotor, cartridge heater, and location of thermocouple for reference and control of heater temperature (Ths). Flow path of forced cooling air also shown.

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Figure 3

Schematic view of GFB rotordynamic test rig with cartridge heater. T1–T16, Tamb, and Th represent locations of temperature measurement.

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Figure 4

Test condition 1: Amplitude of rotor synchronous response versus rotor speed. Slow roll compensation at 2 krpm. Tests at room temperature and with (a) heater off and (b) heater on at Ths=360°C. No axial cooling flow into bearings.

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Figure 5

Test condition 1: Phase difference (∠FH−∠DH) and major amplitude ratio (|DV2+DH2/FV2+FH2|) of recorded imbalance response. No induced rotor heating (heater off). No axial cooling flow into bearings.

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Figure 9

Test condition 2: Temperatures versus elapsed test time for operation without a forced cooling flow into bearings and with heater at temperature (Ths)=100°C, 200°C, 300°C, and 360°C. Temperature rises of cartridge heater (Th-Tamb), rotor free end (FE): (T11-Tamb), rotor drive end (DE): (T12-Tamb), and FE and DE bearing cartridges (T1-Tamb) and (T6-Tamb). Rotor speed=30 krpm.

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Figure 10

Test conditions 2–5: Temperatures versus elapsed test time for operation with increasing strengths of cooling stream (maximum of 150 l/min per bearing). (a) Cartridge heater temperature (Th) at 100°C, 200°C, 300°C, and 360°C; (b) temperature rises in FE and DE cartridges, (T1-Tamb) and (T6-Tamb). Rotor speed=30 krpm.

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Figure 11

Test conditions 2–5: Effect of strength of cooling flow on bearing temperatures. Operation with cartridge heater reference temperature (Ths) at 100°C and 200°C. Temperature rise in FE and DE bearing cartridges, (T1-Tamb) and (T6-Tamb) versus cooling flow rate. Rotor speed of 30 krpm.




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