1. School of Aerospace Engineering MITE A Ph.D. Proposal Saeid Niazi Advisor:Lakshmi N. Sankar School of Aerospace Engineering Georgia Institute of Technology Supported by the U.S. Army Research Office Under the Multidisciplinary University Research Initiative (MURI) on Intelligent Turbine Engines Numerical Monitoring of Rotating Stall and Separation Control in Axial Compressors

2. School of Aerospace Engineering MITE Overview l Objectives and Motivation l Surge and Rotating Stall l Mathematical and Numerical Formulation l NASA Axial Rotor 67 Results Background Peak Efficiency Conditions Off-design Conditions l Bleed Valve Control l Conclusions l Proposed Work

3. School of Aerospace Engineering MITE Objectives and Motivation Use CFD to explore and understand compressor stall and surge Develop and test control strategies (bleed valve) for axial compressors Choke Limit Flow Rate Total Pressure Rise Lines of Constant Rotational Speed Lines of Constant Efficiency Surge Limit Desired Extension of Operating Range Safety Margin

4. School of Aerospace Engineering MITE What is Rotating Stall? Rotating stall is a 2-D unsteady local phenomenon Types of rotating stall: Part-span Full-span

5. School of Aerospace Engineering MITE What is Surge? Surge is a global 1-D instability that can affect the whole compression system. In contrast to rotating stall, the average flow through the compressor is unsteady. Pressure Rise Flow Rate Mean Operating Point Limit Cycle Oscillations Pressure Rise Flow Rate Deep Surge Mild Surge Pressure Rise Flow Rate Modified Surge Flow is not symmetric

6. School of Aerospace Engineering MITE Most research activities were on 2-D bases. — Jonnavithula, Sisto, (Stevens Institute of Technology) 1990 — Elder (Cranfield Institute of Technology) 1993 — Rivera (Georgia Tech) 1997 A few research activities were on 3-D Study, such as, He (university of Durham) 1998. Computational Background on Rotating Stall

7. School of Aerospace Engineering MITE Air-injection Murray (CalTech) Fleeter, Lawless (Purdue) Weigl, Paduano, Bright (MIT & NASA Glenn ) Movable plenum wall Gysling, Greitzer, Epstein (MIT) Guide vanes Dussourd (Ingersoll-Rand Research Inc.) Diffuser bleed valves Pinsley, Greitzer, Epstein (MIT) Parsad, Numeier, Haddad (GT) How to Control Stall Bleed Valves Air InjectionGuide Vanes Movable Plenum Walls

8. School of Aerospace Engineering MITE MATHEMATICAL FORMULATION    t q  dV  E ˆ i  F ˆ j  G ˆ k     ndS  R ˆ i  S ˆ j  T ˆ k     ndS Reynolds Averaged Navier-Stokes Equations in Finite Volume Representation: where, q is the state vector. E, F, and G are the inviscid fluxes, and R, S, and T are the viscous fluxes. A cell-vertex finite volume formulation using Roe’s scheme is used for the present simulations.

9. School of Aerospace Engineering MITE MATHEMATICAL FORMULATION The viscous fluxes are computed to second order spatial accuracy. A three-factor ADI scheme with second- order artificial damping on the LHS is used to advance the solution in time. The Spalart-Allmaras turbulence model is used in the present simulations.

10. School of Aerospace Engineering MITE Boundary Conditions Inlet: p 0,T 0,v,w specified; Riemann- Invariant extrapolated from Interior Exit:. m t specified; all other quantities extrapolated from Interior Solid Walls: no-slip velocity conditions; dp/dn=d  dn = 0 Zonal Boundaries: Properties are averaged on either side of the boundary Periodic Boundaries: Properties are averaged on either side of the boundary

11. School of Aerospace Engineering MITE mcmc. Conservation of mass: Outflow Boundary Conditions Outflow Boundary Plenum Chamber u(x,y,z) = 0 p p (x,y,z) = CT. isentropic mtmt. a p, V p Actual mass flow rate Desired mass flow rate All other quantities extrapolated from interior

12. School of Aerospace Engineering MITE Axial Compressor (NASA Rotor 67) 22 Full Blades Inlet Tip Diameter 0.514 m Exit Tip Diameter 0.485 m Tip Clearance 0.61 mm Design Conditions: –Mass Flow Rate 33.25 kg/sec –Rotational Speed 16043 RPM (267.4 Hz) –Rotor Tip Speed 429 m/sec –Inlet Tip Relative Mach Number 1.38 –Total Pressure Ratio 1.63 –Adiabatic Efficiency 0.93 514 mm

13. School of Aerospace Engineering MITE Literature Survey of NASA Rotor 67 Computation of the stable part of the design speed operating line: NASA Glenn Research Center (Chima, Wood, Adamczyk, Reid, and Hah) MIT (Greitzer, and Tan) U.S. Army Propulsion Laboratory (Pierzga) Alison Gas Turbine Division (Crook) University of Florence, Italy (Arnone ) Honda R&D Co., Japan (Arima) Effects of tip clearance gap: NASA Glenn Research Center (Chima and Adamczyk) MIT (Greitzer) Shock boundary layer interaction and wake development: NASA Glenn Research Center (Hah and Reid). End-wall and casing treatment: NASA Glenn Research Center (Adamczyk) MIT (Greitzer)

14. School of Aerospace Engineering MITE Axial Compressor (NASA Rotor 67) 4 Blocks 73X32X21 Total of 196224 cells Meridional Plane Plane Normal to Streamwise Hub LE TE

15. School of Aerospace Engineering MITE Relative Mach Contours at Mid-Span (Peak Efficiency) Spatially uniform flow at design conditions  IV III II I LE TE

16. School of Aerospace Engineering MITE % 30 Pitch Relative Mach Number at %90 Radius (Peak Efficiency) TELE % 50 Pitch TELE

17. School of Aerospace Engineering MITE Shock-Boundary Layer Interaction (Peak Efficiency) LE TE Shock Near Suction Side

18. School of Aerospace Engineering MITE LE TE Shock Velocity Profile at Mid-Passage (Peak efficiency) Flow is well aligned. Very small regions of separation observed in the tip clearance gap(Enlarged view) % Mass Flow rate Fluctuations % Pressure Fluctuations Fluctuations are very small (2%)

19. School of Aerospace Engineering MITE LE TE Clearance Gap Enlarged View of Velocity Profile in the Clearance Gap (Peak efficiency) The reversed flow in the gap and the leading edge vorticity grow in size and magnitude as the compressor operates at off- design conditions

20. School of Aerospace Engineering MITE Adiabatic Efficiency (NASA Rotor 67) Peak Efficiency Near Stall

21. School of Aerospace Engineering MITE Peak Efficiency Near Stall Unstable Conditions Controlled A BC Performance Map (NASA Rotor 67) measured mass flow rate at choke: 34.96 kg/s CFD choke mass flow rate: 34.76 kg/s D

22. School of Aerospace Engineering MITE Transient of Massflow Rate Fluctuations (A) Peak Efficiency (C) Modified Surge (B) Mild Surge Rotor Revolutions ( 

23. School of Aerospace Engineering MITE I IIIII IV LE TE  I II III IV Location of the Probes for Observing the Pressure and Velocity Fluctuations The probes are located at 30% chord upstream of the rotor and 90% span. They are fixed in space.

24. School of Aerospace Engineering MITE Onset of the Stall (Clean Inlet) Probes show identical fluctuations. Flow while unsteady, is still symmetric from blade to blade. I IIIII IV  Time (Rotor Revolution ) I II III IV

25. School of Aerospace Engineering MITE NASA Rotor 67 Results (surge Conditions) f= 1/80 of blade passing frequency

26. School of Aerospace Engineering MITE NASA Rotor 67 Results (Rotating Stall) 

27. School of Aerospace Engineering MITE NASA Rotor 67 Results (Rotating Stall)

28. School of Aerospace Engineering MITE Onset of the Stall (Disturbed Inlet) Inlet distortion simulated by dropping the stagnation pressure in one block by 20% Flow is no longer symmetric from blade to blade. Frequency of rotating stall is N , where  : blade passing frequency 

29. School of Aerospace Engineering MITE Bleed Valve Control Bleed Area  Hub Shroud Pressure, density and tangential velocities are extrapolated from interior.. U n = m b /(  A b )

30. School of Aerospace Engineering MITE Bleed Valve Control 3% Bleeding nearly eliminates reversed flow near LE

31. School of Aerospace Engineering MITE Bleed Valve Control % Mass Flow Rate Fluctuations % Total Pressure Fluctuations Without Control With Bleed Valve 3% bleed air reduces the total pressure fluctuations by 75%

32. School of Aerospace Engineering MITE Bleed Valve Control Axial Velocity Near LE % From Hub After 1.5 Rev. After 0.5 Rev. Bleed Valve.

33. School of Aerospace Engineering MITE Conclusions The CFD compressor modeling was applied to the NASA Rotor 67 axial compressor. The calculated shock strength and location at the peak efficiency are in good agreement with experimental results. For the axial compressor, tip leakage vortex is stronger under off-design conditions compared to peak efficiency conditions.

34. School of Aerospace Engineering MITE Results revealed that instabilities during the onset of stall in NASA Rotor67 is of mild surge type. The mild surge was followed by a modified surge. (Surge and rotating stall interaction) When flow in the inlet at the onset of the stall was disturbed, flow-field became asymmetric and rotating stall was triggered. Stall and surge can be eliminated by the use of small amounts of bleeding from the diffuser. Conclusions (Continued…)

35. School of Aerospace Engineering MITE Proposed Work Should recent Rotor 37 rotating stall data become publicly available (Contact: Dr. Michelle Bright, NASA Glenn), rotating stall control of Rotor 37 will be attempted. Two additional types of bleed control will be studied. Bleed A : Rotating stall amplitude    Rotating stall frequency n : 1 (linear control) 2 (quadratic control) 