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Research Papers: Hydrodynamic Lubrication

Thermohydrodynamic Model Predictions and Performance Measurements of Bump-Type Foil Bearing for Oil-Free Turboshaft Engines in Rotorcraft Propulsion Systems

[+] Author and Article Information
Tae Ho Kim

Energy Mechanics Research Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Songbuk-gu, Seoul 136-791, Koreathk@kist.re.kr

Luis San Andrés

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123lsanandres@tamu.edu

Note that ambient temperature does not remain constant during the lengthy elapsed testing times.

J. Tribol 132(1), 011701 (Nov 11, 2009) (11 pages) doi:10.1115/1.4000279 History: Received April 24, 2009; Revised September 15, 2009; Published November 11, 2009; Online November 11, 2009

An engineered thermal management is fundamental to the application of gas foil bearings (GFBs) as turboshaft supports in rotorcraft propulsion systems. The paper presents a model for the thermal energy transport in a rotor-GFB system operating at high temperature with typical inner and/or outer cooling flows. Predicted film temperatures agree with published test data, demonstrating the effectiveness of an outer cooling stream to remove heat and to control the operating temperature. The inner flow stream is not as efficient. The analysis shows paths of thermal energy by conduction and convection to assist in the design and troubleshooting of rotor-GFB systems operating hot. Bearing temperatures and shaft motions measurements are obtained in a test rotor electrically heated to 132°C. In speed-up tests to 26 krpm, the rotor motion amplitude drops suddenly just above the critical speed, thus, evidencing the typical hardening of compliant bearings. At the hottest test condition, since air is more viscous, the rotor peak motion amplitude decreases, not showing a jump. The coastdown tests show the critical speed increases slightly as the temperature increases.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic side view of foil bearing with inner cooling stream (TCi,PCi) flowing through the hollow shaft and the outer cooling stream (TCo,PCo) flowing through the thin film region and underneath the top foil. Outer cooling flow exits to ambient pressure (Pa). Taken from Ref. 19.

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Figure 2

Nomenclature for temperatures in foil bearing with cooling gas streams and schematic representation of heat flows. Taken from Ref. 19.

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Figure 3

Predicted gas film temperature fields in GFB with rotor speed of 20 krpm and static load Ws=89 N. (a) Without cooling flows, (b) with outer cooling flow (350 l/min), and (c) with inner (350 l/min) and outer (350 l/min) cooling flows. Air supply and ambient temperature (TCi=TCo=T∞) at 21°C.

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Figure 4

Predicted radial temperature profile in foil bearing and shaft system: (a) without cooling flows, (b) with outer cooling flow (350 l/min), and (c) with inner (350 l/min) and outer (350 l/min) cooling flows. Air supply and ambient temperature (TCi=TCo=T∞) at 21°C. Rotor speed of 20 krpm and static load Ws=89 N.

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Figure 5

Thermal energy transport and balance in gas foil bearing and shaft system: (a) without cooling flow, (b) with outer cooling flow (350 l/min), and (c) with inner (350 l/min) and outer (350 l/min) cooling flows. Air supply and ambient temperature (TCi=TCo=T∞) at 21°C. Rotor speed of 20 krpm and static load Ws=89 N.

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Figure 6

Predicted peak film temperature versus strength of cooling stream. Predictions for conditions with (a) outer cooling flow and (b) outer and inner flows. Air supply and ambient temperature (TCi=TCo=T∞) at 21°C. Rotor operation at 20 krpm and 40 krpm with static load Ws=89 N.

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Figure 7

Test rig for high temperature and rotordynamic measurements of a rotor supported on foil bearings

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Figure 8

Schematic view of rotordynamic test rig with cartridge heater and instrumentation for operation at high temperature. Numbers in circles denote locations of temperature measurement.

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Figure 9

Second generation bump type test GFB and its dimensions

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Figure 10

Schematic representation of test foil bearing with five thermocouples placed in machined axial slots. Five temperature measurement locations (Θ=22, 94, 166, 238, and 310 deg) at bearing midplane.

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Figure 11

Measured (averaged) drive end bearing OD surface temperature ((TDB−Ta)/Ta) versus rotor speed. Operation at two heater temperatures (Tc=93°C and 132°C) and at ambient temperature (Tc=Ta=22°C). No cooling flow for cases 1–3 and axial cooling flow (Q∼56 l/min) for cases 4–6.

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Figure 12

Measured shaft surface temperature ((TDS−Ta)/Ta) versus rotor speed. TDS measured at rotor drive end. Operation at two heater temperatures (Tc=93°C and 132°C) and at ambient temperature (Tc=Ta=22°C). No cooling flow for cases 1–3 and axial cooling flow (Q∼56 l/min) for cases 4–6.

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Figure 13

Test rig casing surface temperature (TDC−Ta)/Ta versus rotor speed. Operation at two heater temperatures (Tc=93°C and 132°C) and at ambient temperature (Tc=Ta=22°C). Measurements on side of drive end bearing. No cooling flow for cases 1–3 and axial cooling flow (Q∼56 l/min) for cases 4–6.

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Figure 14

Amplitudes of rotor synchronous response versus speed: (a) speed-up and (b) coast down tests to/from 26 krpm. Operation at two heater temperatures (Tc=93°C and 132°C) and at ambient temperature (Tc=Ta=22°C). Measurements at rotor drive end, vertical plane. Test cases 1–3. No cooling flow.

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Figure 15

Waterfalls of rotor coast down response from 26 krpm. Operation at two heater temperatures (Tc=93°C and 132°C) and at ambient temperature (Tc=Ta=22°C). Measurements at rotor drive end and vertical plane. Test cases 1–3. No cooling flow.

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Figure 16

Test rotor surface condition (a) before and (b) after heating up to Tc∼200°C. Ambient temperature (Ta)=22°C.

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Figure 17

Measured drive end foil bearing cartridge temperatures (TDB−Ta)/Ta versus circumferential location. Operation with increasing rotor speed to 26 krpm. Heater temperature Tc=93°C (case 2). See Fig. 8 for locations of temperature measurement.

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