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

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

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]

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]

Motivation

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

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

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

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

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 12300 rpm was imparted to the blade and the hub.

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

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

Streamtubes of Entropy Baseline Split Tip

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

Pressure ratio speedline

Efficiency Speedline

Results

ANSYS Structural Analysis Blade material Inconel 718 Rotational Velocity of 12300 rpm Fixed Support at the hub Zero displacement constraint in axial direction

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

Results Zoomed image near the split

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

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

Questions

References http://selair.selkirk.bc.ca/training/aerodynamics/range_jet.htm D. C. Wisler, Loss reduction in axial flow compressors through low speed model testing, ASME Journal of Engineering for Gas Turbines and Power http://en.wikipedia.org/wiki/Flight_feather https://hub.united.com/en-us/news/company-operations/pages/new-split-scimitar-winglets-take-flight-on-united-737800.aspx Siddappaji, K., and Turner, M., June 11-15, 2012. General capability of parametric 3d blade design tool for turbomachinery. In Proceedings of ASME Turbo Expo 2012 (gtst.ase.uc.edu/3DBGB)

Backup slides

Results 0.625% Tip Clearance Stall Operating point Choke

Results 1.25% Tip Clearance Stall Operating Point Choke

Results 2.5% Tip Clearance Stall Operating point Choke

Results 3.75% Tip Clearance Operating point Choke Stall

Results 5% Tip Clearance Stall Operating point Choke

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