Title: Computational Analysis of Stall and Separation Control in Compressors
1Computational 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
2Overview
- Recap of Last Presentation
- NASA Axial Rotor 67 Results
- Design Conditions
- Off-Design Conditions
- DLR Centrifugal Results
- Conclusions
- Future Work
3Recap 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
4 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
5Relative Mach Number at 10 Span (Design
Conditions)
6Relative Mach Contours at Mid-Span (Design
Conditions)
Spatially uniform flow at design conditions
7Shock-Boundary Layer Interaction (Design
Conditions)
8Shock-Boundary Layer Interaction (Design
Conditions)
9Velocity Profile at Mid-Passage (Design
Conditions)
- Flow is well aligned.
- Very small regions of separation observed in the
tip clearance gap(Enlarged view)
10Enlarged 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
11Performance Map (NASA Rotor 67)
- measured mass flow rate at choke 34.96 kg/s
- CFD choke mass flow rate 34.76
kg/s
12Transient of Massflow Rate Fluctuations
13NASA Rotor 67 Results (surge Conditions)
f76.4 Hz 1/3.5 of Rotors frequency
14Location 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
15Onset of the Stall (Clean Inlet)
Probes show same fluctuations and flow is
symmetric
16Onset 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
17DLR 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
18Surge Phenomenon
Animation of stagnation pressure contours shows
unsteady leading edge vortex shedding just before
boundary layer separation
19Air-Injection ResultsAngle of Attack
No Injection
Yaw angle directly affects local angle of attack.
3.2 Injection
20Parametric Air-Injection Study
21Conclusion
- 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.
22Future 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
23Outflow BC (GTTURBO3D)
Conservation of mass
24Massflow Rate at the Onset of the Stall
Iterations
25Bleed Control