This is a slide show I presented at the 2011 AIAA CFD Conference in Honolulu, Hawaii. The research herein was published and presented in 2 journal articles, 6 conferences, and an award-nominated thesis. The presentation focuses on the use of the SST gamma-Re_theta turbulence model and its applicability to the low-Reynolds-number regime.

1. Validation of a Low-Cost Transitional
Turbulence Model for
Low-Reynolds-Number External
Aerodynamics
Joshua Counsil and K. Goni Boulama
Royal Military College of Canada
20th AIAA CFD Conference
June 29, 2011
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2. Outline
Results and
Introduction Discussion Questions
12 3 45
Validation of Conclusion
Model
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3. UAVs, Low-Re flow, and CFD
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4. Introduction
Low-Reynolds Number Flow
Laminar separation without reattachment
Courtesy of Yarusevych et al., 2010
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5. Introduction
Low-Reynolds Number Flow
Laminar Separation Bubble (LSB)
Courtesy of Yarusevych et al., 2010
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6. Introduction
URANS
Unsteady Reynolds-Averaged Navier-Stokes Equations
• Turbulence models
• Approximate envelope (eN) method
• Specified transition point
• γ and Reθ
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7. Introduction
• γ and Reθ
• Empirical Correlations
• e.g., ( γ )( μt ) • e.g., Reθ = ƒ( Tu , dP/dx )
• Transport Equations
• e.g.,
SST γ-Reθ
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8. Turbulence Model and Numerical Setup
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9. Validation of Model
Parameters
• NACA 0012
• Re = 100k
• AoA = 4°
• Tu = 0.1%
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10. Validation of Model
Turbulence Model
• Shear Stress Transport Model (SST)
• Shear Stress Transport Transitional Model (SST γ-Reθ)
• XFLR5 eN Method
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11. Validation of Model
Turbulence Model
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12. Validation of Model
Sensitivity Studies
• 2 domain sizes
• 5 grid resolutions
• 2 grid “qualities”
• 2 timestepping schemes
• 6 turbulence intensities
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13. Validation of Model
Domain Inlet Radius
η = 10c η = 20c
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14. Validation of Model
Airfoil Grid Resolution
134 x 93 380 x 263
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15. Validation of Model
Wake Grid Resolution
267 x 185 217 x 185
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16. Validation of Model
Grid Quality and Timestepping Scheme
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17. Validation of Model
Test of Model against Published Results
NACA 0012
Re = 50k
AoA = 5
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18. Validation of Model
Test of Model against Published Results
NACA 0012
Re = 48k
AoA = 6
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19. Validation of Model
Test of Model against Published Results
NACA 0012
Re = 48k
AoA = 6
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20. Validation of Model
Test of Model against Published Results
SD7003
Re = 60k
AoA = 4
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21. Flow-field Analysis, Parameterization
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22. Results and Discussion
Instantaneous Flow Features
• NACA 0012
• Re = 100k
• AoA = 4
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23. Results and Discussion
Instantaneous Flow Features
• NACA 0012
• Re = 100k
• AoA = 4
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24. Results and Discussion
Instantaneous Flow Features
• NACA 0012
• Re = 100k
• AoA = 4
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25. Results and Discussion
Instantaneous Flow Features
• NACA 0012
• Re = 100k
• AoA = 4
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26. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 50k
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27. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 100k
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28. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 250k
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29. Results and Discussion
Time-Averaged Flow Features
• NACA 0012
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30. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 50k
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31. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 100k
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32. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 250k
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33. Results and Discussion
Time-Averaged Flow Features
NACA 0012
Re = 50k Re = 100k
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34. 34

35. Conclusions
• Many CFD methods for low-Re flow
• Numerical validation verified accuracy of method
• Performance of models
• XFLR5 typically underestimates separation/LSB
• SST γ-Reθ model typically overestimates separation/LSB
• Very good aerodynamic performance estimation
• NACA 0012 at various Re and AoA
• Laminar separation without reattachment
• All AoA = 0 and Re = 50k, AoA = 4
• Laminar separation bubble
• All AoA = 8 and Re = 100k, AoA = 4
• With increase in Re or AoA, LSB shrinks and recedes
• Low-Re causes nonlinear aerodynamic characteristics
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