Computational Analysis of Stall and Separation Control in Compressors

22
School of Aerospace Engineering MITE Computational Analysis of Computational Analysis of Stall and Separation Stall and Separation Control in Control in Compressors 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

description

Computational Analysis of Stall and Separation Control in Compressors. Lakshmi Sankar Saeid Niazi, Alexander Stein School of Aerospace Engineering Georgia Institute of Technology - PowerPoint PPT Presentation

Transcript of Computational Analysis of Stall and Separation Control in Compressors

Page 1: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Computational Analysis of Stall and Computational Analysis of Stall and Separation Control in Separation Control in

CompressorsCompressors

Lakshmi SankarSaeid Niazi, Alexander Stein

School of Aerospace EngineeringGeorgia Institute of Technology

Supported by the U.S. Army Research Office Under the Multidisciplinary University Research Initiative (MURI) on Intelligent Turbine Engines

Page 2: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Motivation and ObjectivesMotivation and Objectives• Use CFD to explore and

understand compressor stall and surge

• Develop and test flow control strategies (air-injection, bleeding) for compressors

• Apply CFD to compare low-speed and high-speed configurations

Compressor instabilities can cause fatigue and damage to entire engine

Page 3: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Summary of Earlier AccomplishmentsSummary of Earlier Accomplishments

• 2-D rotating stall was numerically modeled, and the underlying physical phenomena studied

• A 3-D flow solver capable of modeling unsteady viscous flow through axial and centrifugal compressors was developed and validated

• The mechanisms behind the onset and growth of surge in NASA Low Speed Centrifugal Compressor was studied

• Control of Surge through diffuser bleed was simulated

Page 4: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

• Diffuser bleed valves•Pinsley, Greitzer, Epstein (MIT)•Prasad, Neumeier, Haddad (GT)

• Movable plenum wall•Gysling, Greitzer, Epstein (MIT)

• Guide vanes•Dussourd (Ingersoll-Rand Research Inc.)

• Air-injection•Murray (Cal Tech)•Fleeter, Lawless (Purdue)•Weigl, Paduano, Bright (MIT & NASA Lewis)

How to Control Surge (Passive Control)How to Control Surge (Passive Control)

Bleed Valves

Movable Plenum Walls

Guide Vanes

Air-Injection

Page 5: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Boundary Conditions (GTTURBO3D)Boundary Conditions (GTTURBO3D)

Outflow boundary(coupling with plenum)

Periodic Boundaryat compressor inlet

Solid Wall Boundaryat compressor casing

Periodic Boundaryat diffuser

Solid Wall Boundaryat impeller blades

Periodic Boundaryat clearance gap

Solid Wall Boundaryat compressor hub

Inflow Boundary

Page 6: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Outflow BC (GTTURBO3D)Outflow BC (GTTURBO3D)

Plenum Chamber•u(x,y,z) = 0 •pp(x,y,z) = const.•isentropic

ap, Vp

mc

.

mt

.

Outflow Boundary

)mm(Va

dtdp

tcp

2pp

Conservation of mass:

Page 7: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLR High-Speed Centrifugal CompressorDLR High-Speed Centrifugal CompressorAGARD Test CaseAGARD Test Case

•24 main blades•30 backsweep•CFD-grid 141 x 49 x 33 (230,000 grid-points)

Design Conditions:•22360 RPM•Mass flow = 4.0 kg/s•Total pressure ratio = 4.7•Adiab. efficiency = 83%•Exit tip speed = 468 m/s•Inlet Mrel = 0.92

Page 8: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Off-Design Conditions)DLRCC-Results (Off-Design Conditions) Performance Characteristic MapPerformance Characteristic Map

Unsteady fluctuations are denoted by size of circles

Fluctuations at 3.1 kg/sec are 30 times larger than at 4.6 kg/sec

33.23.43.63.8

44.24.44.64.8

55.2

2 2.5 3 3.5 4 4.5 5

Mass Flow (kg/s)

Experiment

CFDTota

l Pre

ssur

e R

atio

Page 9: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Surge Conditions)DLRCC-Results (Surge Conditions)

Mild surge develops.

Surge amplitude grows to 60% of mean flow rate.

Surge frequency = 94 Hz (1/100 of blade passing frequency)

Page 10: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Surge Conditions)DLRCC-Results (Surge Conditions)

Flow field vectors show two separation zones:• near leading edge• in the diffuser

Mild surge cycle colored by Mrel

Page 11: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Surge Conditions)DLRCC-Results (Surge Conditions) Stagnation pressure contoursStagnation pressure contours

•Vortex shedding causes reversed flow•Origin of separation occurs at leading edge pressure side

Direction of rotation

Page 12: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

LSCC-Results (Air-Injection)LSCC-Results (Air-Injection)

Injection angle, = 5º3 to 10% injected mass flow rate

0.04RInletCasing

Rotation Axis

Impeller

RInlet

Page 13: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Air-Injection)DLRCC-Results (Air-Injection) Different yaw angles, 3% injected mass flow rateDifferent yaw angles, 3% injected mass flow rate

Yaw angle directly affects the unsteady leading edge vortex shedding

Positive yaw angle is measured in positive direction of impeller rotation

Page 14: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Air-Injection)DLRCC-Results (Air-Injection)

Leading edge separation suppressed due to injection

Velocity vectors colored by Mrel

Page 15: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Air-Injection)DLRCC-Results (Air-Injection) Different yaw angles, 3% injected mass flow rateDifferent yaw angles, 3% injected mass flow rate

-25

0

25

50

75

100-20 0 20 40 60

Yaw Angle (in Degrees)

Red

uctio

n in

Sur

ge A

mpl

itude

(in

%)

Page 16: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Axial Compressor (NASA Rotor 67)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– 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

Page 17: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Performance Map (NASA Rotor 67)Performance Map (NASA Rotor 67) measured

mass flow rate at choke: 34.96 kg/s

CFD choke mass flow rate: 34.76 kg/s

1.3

1.4

1.5

1.6

1.7

1.8

0.88 0.9 0.92 0.94 0.96 0.98 1

Tota

l Pre

ssur

e ra

tio

Turb

Experiment

laminar

Choke mm

Page 18: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Mach Contours at MidspanMach Contours at Midspan

Spatially uniform flow at design conditions

Page 19: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Summary of Current Year WorkSummary of Current Year Work• The CFD compressor modeling capability was extended to:

• Higher speed, higher pressure compression systems• Turbulence model• Shock capturing capability • Boundary conditions

• Development of surge mechanism in centrifugal compressors was studied. Surge Control through upstream injection was optimized

• In preparation for rotating stall simulations, a multi-blade passage version of the solver was developed and validated

Page 20: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Future and Planned ActivitiesFuture 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

Page 21: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

Technology Transition• The suite of codes may be used by industry partners for pilot studies of promising concepts:

• Compact size of the code• Optimized for turbomachinery applications• Advanced analysis features (fifth order Roe solver, implicit

time marching algorithm, Spalart-Allmaras model) • Documentation is available

• Optimized injection control scheme may be implemented in real engines:

• Injection location• Injection rates• Injection angles

Page 22: Computational Analysis of Stall and Separation Control in  Compressors

School of Aerospace Engineering

MITE

DLRCC-Results (Design Conditions)DLRCC-Results (Design Conditions) Static Pressure Along ShroudStatic Pressure Along Shroud

Excellent agreement between CFD and experiment

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1Meridional Chord, S/Smax

Experiment

CFD

Loca

l Sta

tic P

ress

ure,

p/p

std