Computational Analysis of Stall and Separation Control in Compressors

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Computational Analysis of Stall and Separation
Control in Compressors
Lakshmi Sankar Saeid Niazi, Alexander
Stein 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

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Overview

• Recap of Last Presentation
• NASA Axial Rotor 67 Results
• Design Conditions
• Off-Design Conditions
• DLR Centrifugal Results
• Conclusions
• Future Work

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Recap of Last Presentation

• The CFD compressor modeling was applied to higher
  speed, higher pressure compression systems
• Development of surge mechanism in centrifugal
  compressors was studied. Surge Control through
  upstream injection was optimized (Advisory Board)
• For the axial compressor, tip leakage vortex is
  stronger under off-design conditions compared to
  design conditions. This may cause the compressor
  to go into an unstable state

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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
• 22 Full Blades

• 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

Multi-flow-passage-grid for rotating stall
modeling
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Relative Mach Number at 10 Span (Design
Conditions)
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Relative Mach Contours at Mid-Span (Design
Conditions)
Spatially uniform flow at design conditions
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Shock-Boundary Layer Interaction (Design
Conditions)
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Shock-Boundary Layer Interaction (Design
Conditions)
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Velocity Profile at Mid-Passage (Design
Conditions)

• Flow is well aligned.
• Very small regions of separation observed in the
  tip clearance gap(Enlarged view)

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Enlarged View of Velocity Profile in the
Clearance Gap (Design Conditions)

• The reverse flow in the gap and the leading edge
  vorticity are growing as the compressor goes to
  the off-design conditions

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Performance Map (NASA Rotor 67)

• measured mass flow rate at choke 34.96 kg/s
• CFD choke mass flow rate 34.76
  kg/s

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Transient of Massflow Rate Fluctuations
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NASA Rotor 67 Results (surge Conditions)
f76.4 Hz 1/3.5 of Rotors frequency
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Location of the Probes to Calculate the Pressure
and Velocity Fluctuations
The probes are located at 30 chord upstream
of the rotor and 90 span and are fixed
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Onset of the Stall (Clean Inlet)
Probes show same fluctuations and flow is
symmetric
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Onset of the Stall (Disturbed Inlet)
Inlet stagnation pressure in Block II is Reduced
by 20 Flow is asymmetric and the frequency of
rotating stall is 1337 Hz
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DLR Centrifugal Compressor
24 main blades CFD-grid 141 x 49 x 33
(230,000 grid-points) 22360 RPM Mass flow 4.0
kg/s Total pressure ratio 4.7
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Surge Phenomenon
Animation of stagnation pressure contours shows
unsteady leading edge vortex shedding just before
boundary layer separation
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Air-Injection ResultsAngle of Attack
No Injection
Yaw angle directly affects local angle of attack.
3.2 Injection
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Parametric Air-Injection Study
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Conclusion

• The CFD compressor modeling was applied to
  multi-blade passage axial NASA Rotor 67
  compressor.
• The calculated shock strength and location showed
  good agreement with the experimental results
• When the inlet flow at off-design was
  disturbed, a circumferentially non-uniform flow
  pattern evolved.
• Parametric study revealed optimum air injection
  configuration for DLR centrifugal compressor.

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Future and Planned Activities

• 3-D rotating stall phenomenon and efficient stall
  control in axial compressors (bleeding, vortex
  generators) will be modeled
• Develop a criterion for efficient injection
  control of centrifugal compressors
• Examine the effectiveness of control laws
  developed by Drs. Haddad, Prasad and Neumeier
  through CFD-simulations

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Outflow BC (GTTURBO3D)
Conservation of mass
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Massflow Rate at the Onset of the Stall
Iterations
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Bleed Control