a ph.d. proposal saeid niazi advisor:lakshmi n. sankar school of aerospace engineering

School of Aerospace Engineering

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A Ph.D. Proposal Saeid Niazi

Advisor:Lakshmi N. Sankar

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

Numerical Monitoring of Rotating Numerical Monitoring of Rotating Stall and Separation Control in Axial Stall and Separation Control in Axial

CompressorsCompressors


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OverviewOverview Objectives and Motivation Surge and Rotating Stall Mathematical and Numerical Formulation NASA Axial Rotor 67 Results

• Background• Peak Efficiency Conditions• Off-design Conditions

Bleed Valve Control Conclusions Proposed Work


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Objectives and MotivationObjectives and Motivation

• Use CFD to explore and understand compressor stall and surge

• Develop and test control strategies (bleed valve) for axial compressors

Ch

oke

Lim

it

Flow Rate

To

tal P

ress

ure

Ris

e

Lines of ConstantRotational Speed

Lines of ConstantEfficiency

Surg

e L

imit

Desired Extension of Operating Range

Safety Margin


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What is Rotating Stall?What is Rotating Stall?

• Rotating stall is a 2-D unsteady local phenomenon

• Types of rotating stall:

•Part-span•Full-span


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What is Surge?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

MeanOperating Point

Limit CycleOscillations

Pressure Rise

Flow Rate

Deep Surge

Mild SurgePressure Rise

Flow Rate

Modified Surge

Flow is not symmetric


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• 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 StallComputational Background on Rotating Stall


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• 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 StallHow to Control Stall

Bleed Valves

Air Injection

Guide Vanes

Movable Plenum Walls


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MATHEMATICAL FORMULATION MATHEMATICAL FORMULATION

t

qdV Eˆ i Fˆ j G ˆ k n dS Rˆ i Sˆ j T ˆ k

n dS

Reynolds Averaged Navier-Stokes Equations in FiniteVolume 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’sscheme is used for the present simulations.


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MATHEMATICAL FORMULATIONMATHEMATICAL 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.


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Boundary ConditionsBoundary Conditions

Inlet:p0,T0,v,w specified;Riemann-Invariant extrapolated from Interior

Exit:.mt specified;all other quantities extrapolated from Interior

Solid Walls:no-slip velocity conditions;dp/dn=ddn = 0

Zonal Boundaries:Properties are averaged on either side of the boundary

Periodic Boundaries:Properties are averaged on either side of the boundary


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mc

. )mm(V

a

dt

dptc

p

2pp

Conservation of mass:

Outflow Boundary ConditionsOutflow Boundary Conditions

Outflow Boundary

Plenum Chamberu(x,y,z) = 0 •pp(x,y,z) = CT.•isentropic

mt

.

ap, Vp

Actual mass flow rate:cmDesired mass flow rate:tm

All other quantities extrapolated from interior


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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• 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


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Literature Survey of NASA Rotor 67Literature 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)


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Axial Compressor (NASA Rotor 67)Axial Compressor (NASA Rotor 67)

4 Blocks73X32X21Total of 196224 cells

Meridional Plane

Plane Normal to Streamwise

Hub

LE TE


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Relative Mach Contours at Mid-SpanRelative Mach Contours at Mid-Span (Peak Efficiency)(Peak Efficiency)

Spatially uniform flow at design conditions

IV

III

II

I

LETE


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0.8

1

1.2

1.4

1.6

-125 -50 25 100 175 250% C h o r d

M

CFD

Experiment

% 30 Pitch

Relative Mach Number at %90 Radius (Peak Efficiency)

TELE

0.8

1

1.2

1.4

1.6

-125 -50 25 100 175 250% C h o r d

M

CFD

Experiment

% 50 Pitch

TELE


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Shock-Boundary Layer InteractionShock-Boundary Layer Interaction (Peak Efficiency) (Peak Efficiency)

LE

TE

Shock

Near Suction Side


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LE

TE

Shock

Velocity Profile at Mid-PassageVelocity Profile at Mid-Passage (Peak efficiency) (Peak efficiency)

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

-50

-30

-10

10

30

50

-40 -30 -20 -10 0 10 20 30 40

% Mass Flow rate Fluctuations

% P

ress

ure

Flu

ctua

tion

s

Fluctuations are very small (2%)


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LE

TE

Clearance Gap

Enlarged View of Velocity Profile in Enlarged View of Velocity Profile in the Clearance Gap (Peak efficiency)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


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Adiabatic Efficiency (NASA Rotor 67)Adiabatic Efficiency (NASA Rotor 67)Choke m

m

VdA

VdAp

p

p

p

01

02

01

02

VdA

VdATT

T

T

01

02

01

02

1

1

01

02

1

01

02

TT

pp

ad

0.84

0.86

0.88

0.9

0.92

0.94

0.88 0.9 0.92 0.94 0.96 0.98 1

Eff

icie

ncy

Experiment

CFD

Peak Efficiency

Near Stall


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1.3

1.4

1.5

1.6

1.7

1.8

0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1

Tot

al P

ress

ure

rat

io

TurbExperimentlaminar3% Bleed Air

Peak Efficiency

Near Stall

Unstable Conditions

Controlled

A

BC

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

Choke m

m

D


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Transient of Massflow Rate FluctuationsTransient of Massflow Rate Fluctuations

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 4 8 12 16 20 24 28 32

Ma

ssfl

ow

Ra

te F

luct

ua

tio

ns

(kg

/s)

(A)Peak Efficiency

(C)Modified Surge

(B) Mild Surge

Rotor Revolutions (


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IIIIIIIVLE

TE

I

II

III

IV

Location of the Probes for Observing Location of the Probes for Observing the Pressure and Velocity Fluctuationsthe Pressure and Velocity Fluctuations

The probes are located at 30% chord upstream of the rotor and 90% span. They are fixed in space.


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Onset of the Stall (Clean Inlet)Onset of the Stall (Clean Inlet)

•Probes show identical fluctuations.

•Flow while unsteady, is still symmetric from blade to blade.

IIIIII

IV

0.5

0.8

1.1

1.4

1.7

0.00 0.36 0.73 1.09 1.45 1.82

Pre

ssur

e

Time (Rotor Revolution)

I

II

III

IV


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NASA Rotor 67 ResultsNASA Rotor 67 Results (surge Conditions) (surge Conditions)

f= 1/80 of blade passing frequency


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NASA Rotor 67 ResultsNASA Rotor 67 Results (Rotating Stall) (Rotating Stall)


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0.4

0.7

1

1.3

1.6

0.00 0.36 0.73 1.09 1.45 1.82 2.18 Time (Rotor Revolution)

Pre

ssur

e

Onset of the Stall (Disturbed Inlet)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


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Bleed Valve ControlBleed Valve Control

Bleed Area

Hub

Shroud

• Pressure, density and tangential velocities are extrapolated from interior. .• Un = mb/(Ab)


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Bleed Valve ControlBleed Valve Control3% Bleeding nearly eliminates reversed flow near LE


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Bleed Valve ControlBleed Valve Control

-50

-30

-10

10

30

50

-40 -20 0 20 40

-50

-30

-10

10

30

50

-40 -20 0 20 40

% Mass Flow Rate Fluctuations

% Total Pressure

Fluctuations

Without Control

With Bleed Valve

3% bleed air reduces the total pressure fluctuations by 75%


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Bleed Valve ControlBleed Valve ControlAxial Velocity Near LEAxial Velocity Near LE

% F

rom

Hub

After 1.5 Rev.

After 0.5 Rev.

Bleed Valve.


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ConclusionsConclusions•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.


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•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…)Conclusions (Continued…)


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Proposed WorkProposed 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

tm

)sin()( 10 tABmm nbleed

A : Rotating stall amplitudeRotating stall frequencyn : 1 (linear control) 2 (quadratic control)

a ph.d. proposal saeid niazi advisor:lakshmi n. sankar school of aerospace engineering

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