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TECHNICAL PAPERS

The Boundary Layer Over Turbine Blade Models With Realistic Rough Surfaces

[+] Author and Article Information
Hugh M. McIlroy

Department of Mechanical Engineering,  University of Idaho At Idaho Falls, Idaho Falls, ID 83402mcieng@srv.net

Ralph S. Budwig

Department of Mechanical Engineering,  University of Idaho, Moscow, ID 83844rbudwig@uidaho.edu

J. Turbomach 129(2), 318-330 (Feb 01, 2005) (13 pages) doi:10.1115/1.2218572 History: Received October 01, 2004; Revised February 01, 2005

Results are presented of extensive boundary layer measurements taken over a flat, smooth plate model of the front one-third of a turbine blade and over the model with an embedded strip of realistic rough surface. The turbine blade model also included elevated freestream turbulence and an accelerating freestream in order to simulate conditions on the suction side of a high-pressure turbine blade. The realistic rough surface was developed by scaling actual turbine blade surface data provided by U.S. Air Force Research Laboratory. The rough patch can be considered to be an idealized area of distributed spalls with realistic surface roughness. The results indicate that bypass transition occurred very early in the flow over the model and that the boundary layer remained unstable (transitional) throughout the entire length of the test plate. Results from the rough patch study indicate the boundary layer thickness and momentum thickness Reynolds numbers increased over the rough patch and the shape factor increased over the rough patch but then decreased downstream of the patch. It was also found that flow downstream of the patch experienced a gradual retransition to laminar-like behavior but in less time and distance than in the smooth plate case. Additionally, the rough patch caused a significant increase in streamwise turbulence intensity and normal turbulence intensity over the rough patch and downstream of the patch. In addition, the skin friction coefficient over the rough patch increased by nearly 2.5 times the smooth plate value. Finally, the rough patch caused the Reynolds shear stresses to increase in the region close the plate surface.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of matched-index-of-refraction flow facility with experimental apparatus

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Figure 2

Schematic drawing of test section

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Figure 3

Schematic drawing of turbulence generator

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Figure 4

Schematic drawing of the locations where LDV velocity profile measurements were obtained for the smooth plate base case

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Figure 5

Picture of the complete rough surface of the suction surface of a land-based power turbine rotor blade measured by Bons (4)

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Figure 6

Picture of the scaled rough surface used to fabricate the rough patch in a 4in. by 20in. aluminum plate

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Figure 7

The 4in. by 20in. realistic rough patch installed in the test section of the oil tunnel

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Figure 8

Schematic drawing of the locations where LDV velocity profile measurements were obtained for the rough patch case

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Figure 9

Freestream velocity, acceleration parameter K, Reynolds number based on distance from the leading edge, and freestream turbulence intensity for the smooth plate case with sketch of test plate (dimensions in millimeters)

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Figure 10

Boundary-layer velocity profiles of smooth plate case in Cartesian coordinates

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Figure 11

Streamwise turbulence intensity for the smooth plate case at x=61mm without a turbulence generator installed and with the turbulence generator installed and operating in the active, downstream injection mode

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Figure 12

Boundary layer velocity profiles at locations x=61mmtox=300mm in wall coordinates

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Figure 13

Boundary-layer velocity profiles at locations x=300mmtox=1775mm in wall coordinates

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Figure 14

Boundary-layer thickness and integral parameters for the smooth plate case

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Figure 15

Smooth plate case momentum thickness Reynolds numbers

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Figure 16

(a) Measured streamwise turbulence intensity profiles for upstream half of test plate. (b) Measured streamwise turbulence intensity profiles for downstream half of the test plate.

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Figure 17

(a) Measured normal turbulence intensity profiles at upstream measurement locations where the v component was available. (b) Measured normal turbulence intensity profiles at downstream measurement locations where the v component was available.

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Figure 18

(a) Absolute value of the Reynolds shear stress at upstream measurement locations where the v component was available. (b) Absolute value of the Reynolds shear stress at downstream measurement locations where the v component was available.

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Figure 19

Experiment and theoretical values of the friction coefficient and the boundary-layer shape factor

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Figure 20

Boundary-layer velocity profiles of the rough patch case in Cartesian coordinates

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Figure 21

Boundary-layer velocity profiles of the rough patch case for x=600 to x=795 in wall coordinates

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Figure 22

Boundary-layer velocity profiles of the rough patch case for x=795 to the end of the test plate in wall coordinates

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Figure 23

Boundary-layer thickness for the rough patch case compared to the smooth plate case

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Figure 24

Boundary-layer displacement thickness for the rough patch case compared to the smooth plate case

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Figure 25

Boundary-layer momentum thickness for the rough patch case compared to the smooth plate case

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Figure 26

Boundary-layer displacement thickness and momentum thickness over the rough patch with rough patch profile

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Figure 27

Comparison of the momentum thickness Reynolds number (Reθ) for the smooth plate case and the rough patch case

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Figure 28

(a) Streamwise turbulence intensity for the rough patch case. (b) Streamwise turbulence intensity for the rough patch case.

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Figure 29

Normal turbulence intensity for the rough patch case

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Figure 30

Boundary layer shape factor for the rough patch case compared to the smooth plate case

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Figure 31

Comparison of the maximum absolute value of the Reynolds stresses for the rough patch case and the smooth plate case

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Figure 32

Comparison of the y-location of the maximum absolute value of the Reynolds stresses for the rough patch case and the smooth plate case

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Figure 33

Comparison of skin friction coefficients for the smooth plate case and the rough patch case

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Figure 34

Surface map of rough patch showing location of peak visible to the LDV system

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Figure 35

Blow-up of the rough surface peak with calculated skin friction coefficients

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