This document summarizes research on the effect of 3D printed surface roughness on film cooling effectiveness. Experiments were conducted by manufacturing film cooling holes using different 3D printing techniques that resulted in varying surface roughness. Results showed major differences in film cooling effectiveness and span-averaged results between the 3D printed coupons compared to a standard CNC machined part due to increased surface roughness. Rougher surfaces delayed coolant separation in the holes and showed higher effectiveness at high blowing ratios, likely due to film diffusion preventing penetration into the mainstream flow. Further work is needed to understand the impact of build orientation and other manufacturing effects.

1. Dependence of Film Cooling
Effectiveness on 3D Printed
Cooling Holes
Presented By:
Paul Aghasi
GT2016-56698, June 14th 2016
Paul Aghasi, MSc
Ephraim Gutmark, PhD
David Munday, PhD
Authors, University of Cincinnati:

2. Outline
• Experimental Approach and Motivation
• Relevant Previous Work
• Data Quality and Facility Validation
• Experimental Results
• Discussion and Conclusion
• Backup Slides
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3. Supply System and Wind Tunnel
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Facility Capabilities:
Air Mass flow: up to 3.0 lbm/s
Coolant Mass flow: up to 0.05 lbm/s
Mainstream Mach: up to 0.8
Available Air at Highest Mass Flow: 30 mins

4. Film Hole Geometry
• (a) CNC Aluminum
• (b) SLA
• (c) PolyJet
• (d-f) FDM, 200-250-
300μ build layer
resolutions
1Schroeder R. P., and Thole K. A., 2014. "Adiabatic Effectiveness Measurements For A Baseline Shaped Film Cooling Hole," in Proceedings of ASME Turbo Expo, Düsseldorf,
Germany,
1
Objective:
Similar performance?
If not why?
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5. Roughness and Diffusers
• Ra/D = 0.005
• Added roughness
caused:
– Flow separation
prevention
– BL thickening at the
throat and effective
divergence angle
reduction
1Persh and Bailey B. M., 1954."Effect of Surface Roughness Over the Downstream Region of a 23° Conical Diffuser," NACA TN 3066,
1
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u/U

6. Factors Affecting Part Quality
• Stair stepping effect
• Build orientation
• Surface roughness is method
dependent
• 90° build angle surface roughness
can be related to the 60° build
angle surface roughness
– True for SLA and FDM
– Inverted for PolyJet
30°
1Ahn D., Kim H., and Lee S., 2009. "Surface roughness prediction using measured data and interpolation in layered manufacturing," Journal of Materials
Processing Technology, 209, pp. 664-671,
2Kim G. D., and Oh Y. T., 2008. "A benchmark study on rapid prototyping processes and machines: quantitative comparisons of mechanical properties,
accuracy, roughness, speed, and material cost," Journal of Engineering Manufacture, 222 (2), pp. 201-215,
2
2
1
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2

7. Data Quality – PSP Validation
1Baldauf S., Schulz A., and Wittig S., 2001. "High-Resolution Measurements of Local
Effectiveness From Discrete Hole Film Cooling," ASME Journal of Turbomachinery, 123
(4), pp. 758-765,
δ/D = 0.4
δ/D = 0.1
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8. Experimental Flow Conditions
• Mainstream Mach 0.3 for all cases
• Approach Rex= 9 X 105 > 5 X 105
• CO2 as coolant, density ratio = 1.5
– Mass transfer analogy
• Test conditions:
Blowing Ratio (BR) 1.0 1.5 2.0 2.5 3.0 3.5
Momentum flux ratio (I) 0.58 1.18 1.85 2.52 3.16 3.76
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9. Roughness Measurements
-Bruker Contour GT-K1 3D
Optical Microscope
-White and green light
interferometry
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10. Roughness measurements
Build Layer
Thickness (μm)
Manufacturing
Technique (qty.)
Material Roughness
Ra/D
Observed
Liftoff (BR)
N/A CNC (1)
Bare Al
Painted Al
0.00038
0.00650
2.5
25 (0.010D) PolyJet (3) RGD525 0.00927 2.0
25 (0.010D) SLA (1) Photo-polymer 0.00545 2.0
200 (0.08D) FDM (1) ABS Plastic 0.00896 >3.5
250 (0.10D) FDM (1) ABS Plastic 0.01077 3.0
300 (0.12D) FDM (1) ABS Plastic 0.01288 3.5
1Ahn D., Kim H., and Lee S., 2009. "Surface roughness prediction using measured data and interpolation in layered manufacturing," Journal of Materials
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11. Discharge Coefficient
• PolyJet Cd < FDM Cd
• Highest Cd -> aluminum CNC
• FDM roughness correlating
with Cd
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
DischargeCoefficient
1.0
1.5
2.0
2.5
3.0
3.5
BR:
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
1.0 1.5 2.0 2.5 3.0 3.5
DischargeCoefficient
BR
Aluminum
SLA
PolyJet
FDM 200
FDM 250
FDM 300
Roughness: coarse  smooth
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12. Comparison of various test coupons
at BR = 2.0, 1.85
Comparison of various test coupons at
BR = 1.5, I = 1.18
Full Field Effectiveness
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13. Comparison of various test coupons at
BR = 3.5, I = 3.76
Full Field η
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0 0
0 0
0 0

14. Lift off 2.5
Lift off >3.5
Lift off 2.0Lift off 2.0
Lift off 3.0 Lift off 3.5
Span Averaged Results
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0 0 0
0 0 0

15. Discussion and Conclusion
• OSP increased Ra for aluminum
• Major differences in η and η̅ for 3D printed coupons
– Care needs to be taken when testing 3D printed film holes.
• In-hole coolant separation was delayed for rougher parts
– Most likely due to boundary layer thickening at the diffuser
section1
– The exception is the PolyJet coupon
• Rougher test coupons showed higher η̅ at BR of 3.5
– Due to the film diffusion on the rough surface that prevents it
from penetrating into the mainstream2
• At this scale the roughness produced by additive
manufacturing is not comparable to the less rough, standard
CNC machined parts.
1Persh and Bailey B. M., 1954."Effect of Surface Roughness Over the Downstream Region of a 23° Conical Diffuser," NACA TN
3066,
2Goldstein, R. J. Eckert, E. R. G. Chiang, H. D. and Elovic, E. 1985. "Effect of Surface Roughness on Film Cooling Performance,"
Journal of Engineering for Gas Turbines and Power , 107, pp. 111-116,
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16. Future Work
• Build orientation
• Roughness effects from the paint
• Hot wire measurements
– Oversized holes
• Metal 3D printing and its effect
– Its build orientation
• Assess CFD validation
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17. Thank you!
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