1. 40th Dayton Cincinnati Aerospace Sciences Symposium Novel Split Tip Compressor Blade Design Study
Abhay Srinivas, Kiran Siddappaji and Mark G. Turner
Aerospace Engineering
University of Cincinnati

2. Outline Motivation for the novel split tip blade Process Overview
Geometry Generation
3D CFD Analysis
ANSYS Structural Analysis
Conclusions
Future Work

3. Motivation
Jet engine efficiency goals are driving compressors to higher pressure ratios and engines to higher bypass ratios
Need for higher tip clearance to blade height ratio
Loss in efficiency at large clearances for compressors
[1]
[2]

4. Motivation Alula feathers of a bird
Split winglets in aircrafts also known as Scmitar winglets
Higher efficiency at large clearances
Higher stall margins
3DBGB[5] ability to generate complex geometries easily
[3]
[4]

5. Motivation

6. Process Overview
3D blade section generation in 3DBGB in-house geometry generator
Geometry Generation in Star-CCM+
3D CFD and Structural Analysis

7. Geometry Generation
Sixth rotor of a 10 stage HPC based on GE’s EEE [4] compressor is chosen
Lean was added to the blade above 80% span
Tangential lean was used to create the geometry
Blade with positive lean
Blade with negative lean

8. Geometry Generation 2 blades with equal but opposite lean
Sliced blades
Final Fluid Volume

9. Grid Generation Unstructured mesh using polyhedrals and prism layers
Base cell size of 0.5 mm is used
7 prism layers with a stretching factor of 1.5 is used
Grid dependency study was done and the grid chosen is a balance between accuracy and speed
The grid chosen had a mean y+ values of 14

10. Boundary Conditions
Stagnation inlet boundary condition is used with a Total Pressure and Total Temperature profile being defined.
Radial Equilibrium boundary condition is used at the outlet.
Reynolds Averaged Navier-Stokes solver.
Spalart-Allmaras turbulence model with turbulence viscosity ratio of 500.
A rotation rate of rpm was imparted to the blade and the hub.

11. Boundary Conditions
Absolute velocity profiles at inlet were defined in terms of components
These are held constant for all cases.

12. Relative Mach Number Contours
1.25% clearance case
Baseline
Split Tip
Stall
Operating Point
Choke

13. Streamtubes of Entropy
Baseline
Split Tip

14. Speedlines
5 different tip clearance cases were run, 0.625%, 1.25% (Baseline), 2.5%, 3.75%, 5% (0.5x, 1x, 2x, 3x, 4x)
The back pressure was increased until there was reverse flow at the inlet on 200+ faces.
At this point it was determined that the compressor had stalled

15. Pressure ratio speedline

16. Efficiency Speedline

17. Results

18. ANSYS Structural Analysis
Blade material Inconel 718
Rotational Velocity of rpm
Fixed Support at the hub
Zero displacement constraint in axial direction

19. Results
Maximum Stress = 1353 MPa
Tensile Strength = 1100 MPa at 2270C

20. Results
Zoomed image near the split

21. Conclusion A novel blade geometry has been designed
Effect of tip clearance on the new geometry has been studied
Preliminary study shows that the design had higher operating range than the baseline blade
Tip sensitivity study showed that as the tip clearance was increased the efficiency of the split tip blade was higher than that of the baseline blade

22. Future Work Better understanding of flow physics
Finding optimum lean and depth of cut
Effect of multiple cuts on performance

23. Questions

24. References
D. C. Wisler, Loss reduction in axial flow compressors through low speed model testing, ASME Journal of Engineering for Gas Turbines and Power
Siddappaji, K., and Turner, M., June 11-15, General capability of parametric 3d blade design tool for turbomachinery. In Proceedings of ASME Turbo Expo 2012 (gtst.ase.uc.edu/3DBGB)

25. Backup slides

26. Results 0.625% Tip Clearance
Stall
Operating point
Choke

27. Results 1.25% Tip Clearance
Stall
Operating Point
Choke

28. Results 2.5% Tip Clearance
Stall
Operating point
Choke

29. Results 3.75% Tip Clearance
Operating point
Choke
Stall

30. Results 5% Tip Clearance
Stall
Operating point
Choke

31. Results
Exit corrected flow function
FF(A) = 𝑚∗ 𝑅∗𝑇 𝑜 𝑃 𝑜