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Research Papers: Gas Turbines: Structures and Dynamics

Friction Factor Behavior From Flat-Plate Tests of Smooth and Hole-Pattern Roughened Surfaces With Supply Pressures up to 84 bars

[+] Author and Article Information
Dara W. Childs

Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843dchilds@tamu.edu

Bassem Kheireddin

 Texas A&M University, College Station, TX 77843bkheireddin@live.com

Stephen Phillips

Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843sphillips@tamu.edu

Thanesh Deva Asirvatham

 Texas A&M University, College Station, TX 77843thaneshda@gmail.com

J. Eng. Gas Turbines Power 133(9), 092504 (Apr 19, 2011) (10 pages) doi:10.1115/1.4002882 History: Received August 16, 2010; Revised September 03, 2010; Published April 19, 2011; Online April 19, 2011

A flat-plate tester was used to measure the friction factor behavior for a hole-pattern roughened surface apposed to a smooth surface. The tests were executed to characterize the friction factor behavior of annular seals that use a roughened-surface stator and a smooth rotor. Friction factors were obtained from measurements of the mass flow rate and static pressure measurements along the smooth and roughened surfaces. In addition, dynamic pressure measurements were made at four axial locations at the bottom of individual holes and at facing locations in the smooth plate. The test facility is described, and a procedure for determining the friction factor is reviewed. Three clearances were investigated: 0.635 mm, 0.381 mm, and 0.254 mm. Tests were conducted with air at three different inlet pressures (84 bars, 70 bars, and 55 bars), producing a Reynolds numbers range from 50,000 to 700,000. Three surface configurations were tested, including smooth-on-smooth, smooth-on-hole, and hole-on-hole. The hole-pattern plates are identical with the exception of the hole depth. For the smooth-on-smooth and smooth-on-hole configurations, the friction factor remains largely constant or increases slightly with increasing Reynolds numbers. The friction factor increases as the clearance between the plates increases. The test program was initiated to investigate a friction-factor jump phenomenon cited by Ha (1992, “Friction-Factor Characteristics for Narrow-Channels With Honeycomb Surfaces,” Trans. ASME, J. Tribol., 114, pp. 714–721) in test results from a flat-plate tester where, at elevated values of Reynolds numbers, the friction factor began to increase steadily with increasing Reynolds numbers. They tested apposed honeycomb surfaces. For the present tests, the phenomenon was also observed for tests of apposed roughened surfaces but was not observed for smooth-on-smooth or smooth-on-rough configurations. When the phenomenon was observed, dynamic pressure measurements showed a peak-pressure oscillation at the calculated Helmholtz frequency of the holes.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Detailed view of the flat-plate tester

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Figure 2

(a) Perspective view of smooth plate. (b) Sensor detail of smooth plate. (c) Sensor detail of HP plate.

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Figure 3

Hole-pattern configuration

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Figure 5

Clearance error distribution for the 0.381 mm clearance

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Figure 6

Measured pressure values along test plate (Pin=84 bars, ∅=3.175 mm, hd=3.302 mm, and CPL=0.635 mm)

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Figure 7

Calculated M values for axial locations (Pin=84 bars, ∅=3.175 mm, hd=3.302 mm, and CPL=0.635 mm)

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Figure 8

Friction factor distribution along the axial location (Pin=84 bars, ∅=3.175 mm, hd=3.302 mm, and CPL=0.635 mm)

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Figure 9

ff versus Re for a smooth-on-hole configuration (Pin=84 bars, ∅=3.175 mm, hd=3.302 mm, and CPL=0.635 mm)

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Figure 10

Effect of hd on ff for smooth-on-hole configuration (Pin=84 bars, ∅=3.175 mm, and CPL=0.635 mm)

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Figure 11

ff versus hd for three clearances (Pin=84 bars, ∅=3.175 mm, and Re∼200,000)

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Figure 12

ff versus Re for three clearances (Pin=84 bars, ∅=3.175 mm, and hd=3.302 mm)

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Figure 13

Pressure amplitude spectra for hole-on-smooth configuration

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Figure 14

ff versus Re for hole-on-hole configuration (Pin=84 bars, ∅=3.175 mm, and hd=3.302 mm)

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Figure 15

Frequency spectra for hole-on-smooth configuration (Pin=84 bars, ∅=3.175 mm, hd=3.302 mm, CPL=0.635 mm, and Re∼479,000). The predicted Helmholtz frequency based on average temperature across the plates is ∼25 kHz.

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