This document summarizes a computational study of the effects of protruding stud casing treatment on the performance of an axial transonic turbofan. The study found that protruding studs can expand the fan's stall margin by up to 3.5% by altering the radial flow velocities and angles within the fan. Analysis of the results showed the studs cause further deceleration near the casing and acceleration under the studs, improving the radial flow profile and turning angles across most of the span. Further analysis is still needed to fully understand the mechanisms by which the studs expand the stall margin.

1. Computational Study of the Effects of Protruding
Studs Casing Treatment on the Performance of an
Axial Transonic Turbofan
M. D. Collao R. S. Webster K. Sreenivas W. Lin
Graduate School of Computational Science & Engineering
52nd AIAA/SAE/ASEE Joint Propulsion Conference
July, 2016 - Salt Lake City, Utah

2. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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3. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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4. Motivation
● Find simple ways of extending stability in compression systems.
● Test the potential use of protruding studs as casing treatment.
● Understand changes in flow dynamics from using protruding studs.
● Increase knowledge and skills of turbomachinery and CFD application.
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5. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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6. Flow Solver: Tenasi
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7. Flow Solver: Tenasi
● Parallel
● Unstructured
● Finite Volume
● Node Centered
● Implicit
● Unsteady 3D Navier-Stokes
● Subsonic and Supersonic Regimes
● Inviscid, laminar, turbulent flows
● Internal and external flows
● Supports grid motion and rotating reference frame
● Turbulence modeling: Menter’s one equation SAS, q- , k- /k- hybrid,
Wilcox’s Reynolds Stress, LES, DES
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8. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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9. Turbofan: SDT2-R4
Source: ntrs.nasa.gov
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Source Diagnostic Test
Baseline R4 Fan and Outlet Guide Vanes
Depicted with 55 outlet guide vanes.

10. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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11. Casing Treatment: Origin
Lin (2013) reported testing rings attached to the casing
upstream and downstream of the fan rotor,
separately and together.
The ring located downstream was found to have
minimal impact on pressure ratio and small
negative impact in efficiency.
Other configurations had great negative impact.
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12. Casing Treatment: Protruding Studs
Studs Dimensions - Front View
% dimensions are of chord length at fan blade tip
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Side B Side A
3.27° approx.
Stud 1
4.5%
direction of blade rotation
Casing Surface

13. Casing Treatment: Protruding Studs
Studs Dimensions - Top View
% dimensions are of chord length at fan blade tip
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Side A
Side B
Stud1
3.2%
Upstream
Face
Downstream
Face
direction
of blade
rotation

14. Casing Treatment: Protruding Studs
Alignment of Stud Sides
% dimensions are of chord length at fan blade tip
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Stud1
direction of rotation
stagger
blade
tip
Stud2
- stagger
2.9%

15. Casing Treatment: Protruding Studs
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Studs 2 Studs 1Location of Casing Treatment

16. Casing Treatment: In Literature
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“The original intent behind the control tube
design was to bleed some of the low
momentum fluid discharging from the impeller
and re-inject that fluid at the impeller inlet,
which was shown to benefit impeller stability
in computations by Stein et al. [6]. However,
a stabilizing influence was found to result
simply from the presence of control tubes
in the diffuser. It was not enhanced by
bleed...”
G. J. Skoch, “Experimental Investigation of Centrifugal Compressor Stabilization Techniques,”
Transactions of the ASME, Vol. 125, October 2003, pp. 704-713.

17. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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18. Mesh Generation: Surface
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19. Mesh Generation: Details
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20. Mesh Generation: Applied Boundary Conditions
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I
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Axisymmetric
O
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f
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Sliding

21. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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22. Results: Baseline
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23. Results: Baseline
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24. Results: Casing Treatment
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25. Results: Casing Treatment
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26. Results: Casing Treatment
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27. Results: Casing Treatment
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At 132 kPa back pressure,
operating range extension
for Studs 1 is 3.5% and
for Studs 2 is 2.5%.

28. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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29. Analysis: Location and Data to Sample
The following data plots
are radial distribution of
axial velocity, and radial
distribution of flow angles
and turning angles.
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30. Analysis: Radial Distribution of Axial Velocity
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31. Analysis: Radial Distribution of Axial Velocity
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32. Analysis: Radial Distribution of Axial Velocity
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Studs 1 Studs 2

33. Analysis: Radial Distribution of Relative Flow Angles
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34. Analysis: Radial Distribution of Flow Angles
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Baseline Studs 1 Studs 2
Baseline @ 122.5 kPa
Baseline @ 131 kPa
Studs 1 @ 131 kPa
Studs 2 @ 131 kPa

35. Analysis: Radial Distribution of Flow Angles
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36. Outline
● Motivation
● Flow Solver
● Turbofan
● Casing Treatment
● Mesh Generation
● Results
● Analysis
● Conclusion
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37. Conclusion
● Protruding studs were tested as a form of casing treatment.
● Computations suggest that protruding studs can expand stall margin.
● Further analysis is needed to arrive at deep understanding of mechanisms
leading to stall margin expansion.
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38. Conclusion: From Analysis
From the analysis of radial distribution of axial velocities:
● The velocity profile is similar with or without the protruding studs.
● Using the protruding studs, the flow further decelerates near the casing and
accelerates in the region under the protruding stud.
● The highest acceleration occurs between 75% and 90% of span.
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39. Conclusion: From Analysis
From the analysis of radial distribution of relative flow angles and turning angles:
● Near the casing, alignment of relative flow with axis is worse with studs.
● Away from the casing, alignment of relative flow with axis is better with studs.
● The behavior above is analogous to the one observed for axial velocities.
● With casing treatment in use, turning angles are greater up to 95% of span.
This effect peaks at 90% of span.
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40. Upcoming Work
● Continue analysis of solutions.
●
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41. Acknowledgments
The support for this project from the Tennessee Higher Education
Commission is gratefully acknowledged.
Images were created and data extractions carried out using
FieldView as provided by Intelligent Light through its University
Partners Program.
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42. The End
Thanks!
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