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School of Aerospace Engineering. Overview. Research Team. Problem Statement. Objectives. List Of Accomplishments. Significant Findings. Future Work. MITE. School of Aerospace Engineering. Research Team. PI’s: Dr. J.V.R. Prasad Dr. Y. Neumeier Post Doctoral Fellows:

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School of Aerospace Engineering

Overview

Research Team

Problem Statement

Objectives

List Of Accomplishments

Significant Findings

Future Work

MITE


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School of Aerospace Engineering

Research Team

PI’s: Dr. J.V.R. Prasad

Dr. Y. Neumeier

Post Doctoral Fellows:

Dr. N. Markopoulos

Dr. M. Lal (Took up a position

in ME School)

Graduate Students:

Mr. A. Krichene, AE, Ph.D. student

Dr. C. Rivera, AE (graduated)

Dr. T-Y. Ziang, AE (graduated)

Mr. R. Swaminathan, AE (graduated)

Mr. S. Bae, AE (graduated)

Mr. A. Meehan, ME (graduated)

MITE


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Problem Statement

Rotating stall and surge limit the operationof modern

day turbine engine compressors due to associated severe

loss of performance, component failure, etc.

Current practice is to limit operation with roughly

20% stall marginand limitations on fuel flow authority

during acceleration and decelerations, representing

loss of opportunity

Active and/or passive control strategiescan result in

reduced stall margin that will correspond to reduced

weight and fuel savings


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School of Aerospace Engineering

Objectives

Improved understanding of compressor stall and

surge phenomena through modeling, simulation and

experimentation

Investigation of Passive and active control mechanisms

for reducing compressor stall and surge

Development of hybrid control methods by combining

control-theoretic and decision-theoretic techniques

MITE


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School of Aerospace Engineering

List of Accomplishments

Using theoretical extensions to Moore-Greitzer model to include

finite duct effects, analytically showed that the inlet shape affects

the stall inception point in axial compressors. This finding has an

important bearing on the design of appropriate inlets for passive

control of rotating stall. (Presented a paper at the 1999 JPC)

Further experimental evaluations of passive control schemes for

suppression of rotating stall. (Presented a paper at the 1999 IEEE

Conference on Control Applications)

Combined the backstepping control method from the literature

with the adaptive neural net/fuzzy logic scheme for improving

robustness of the controller and evaluated the scheme in simulations.

(Presented papers at the 1999 JPC and 1999 AIAA GNC)

MITE


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School of Aerospace Engineering

List of Current Year Accomplishments (Continued)

Implemented the observer scheme for on-line identification of stall

precursor waves and experimentally evaluated a novel active control

scheme based on stall precursors for active surge control in the

centrifugal compressor experimental facility at Georgia Tech.

MITE


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School of Aerospace Engineering

List of Accomplishments

Using theoretical extensions to Moore-Greitzer model to include

finite duct effects, analytically showed that the inlet shape affects

the stall inception point in axial compressors. This finding has an

important bearing on the design of appropriate inlets for passive

control of rotating stall. (Presented a paper at the 1999 JPC)

Experimental evaluations of passive control schemes for

suppression of rotating stall. (Presented a paper at the 1999 IEEE

Conference on Control Applications)

Combined the backstepping control method from the literature

with the adaptive neural net/fuzzy logic scheme for improving

robustness of the controller and evaluated the scheme in simulations.

(Presented papers at the 1999 JPC and 1999 AIAA GNC)

MITE


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School of Aerospace Engineering

MODELING OF COMPRESSOR ROTATING STALL

AND SURGE - RECENT PROGRESS

by

N. Markopoulos

MITE


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School of Aerospace Engineering

  • PREVIOUS WORK…

  • Complete stability analysis of the Moore-Greitzer model under

    stall amplitude feedback

  • REASONS FOR THE MODELING WORK…

  • Moore-Greitzer model highly approximate - does not predict correct

    r.s. frequency, does not include effects of finite compressor length

  • Moore has suggested in a patent that a separator would eliminate rotating

    stall – we showed experimentally that this is not true

  • To our knowledge, there is no model that takes into account at a

    fundamental level of compressibility effects is available in the open

    literature - Mach numbers between 0.4 – 0.6

  • No control oriented models available for centrifugal compressors

  • Bottom line: Develop a basic physical understanding of the phenomena

    that we are trying to control

MITE


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School of Aerospace Engineering

Schematic of a Compressor

MITE


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School of Aerospace Engineering

  • Our model:

  • Moore-Greitzer model:

  • When Q = 0 the two models become qualitatively the same

  • Moore-Greitzer model is obtained as a limiting case from our model

    as the inlet and outlet duct lengths go to infinity

  • For our model stall inception occurs slightly before or beyond the peak –

    depending on the sign of Q, representing the effect of the inlet

MITE


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School of Aerospace Engineering

COMPARISON WITH THE MOORE-GREITZER MODEL…

  • Stall inception point

  • M-G:Ours:

  • Stable operation

  • M-G:Ours:

  • Unstable operation

  • M-G:Ours:

  • Conclude: It is very desirable to have Q > 0 for delaying loss of stability

MITE


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School of Aerospace Engineering

MAIN RESULTS ON MODELING SO FAR…

  • Quantitative account of instability dynamics for axial compressors -

    extends well-known Moore-Greitzer model

  • Chief difference effect of finite inlet and outlet duct lengths

  • What happens at entrance to inlet slightly hastens or delays settling of

    instabilities before or beyond peak of compressor map

  • Predicted r. s. frequency higher than Moore-Greitzer and function of

    compressor inlet length

  • Needed: a more fundamental account of effect of inlet in terms of

    inlet design parameters - future work

  • Brings up practical questions for the design of inlets and control of

    instabilities - transition to industry

MITE


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School of Aerospace Engineering

CURRENT WORK – AXIAL COMPRESSORS…

  • Axial velocity in real compressors varies between 150 to 200m/sec

    corresponding to Mach numbers between 0.4 and 0.6

  • Inclusion of compressibility effects into our model

  • Governing equation isClassical wave eq. rather than Laplace’s eq.

  • Implies two qualitatively different types of disturbances (bound and scattering)

CURRENT WORK – CENTRIFUGAL COMPRESSORS…

  • Disturbance analysis for purely radial flow

  • Disturbance theory and modeling for centrifugal compressors

MITE


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School of Aerospace Engineering

List Accomplishments

Using theoretical extensions to Moore-Greitzer model to include

finite duct effects, analytically showed that the inlet shape affects

the stall inception point in axial compressors. This finding has an

important bearing on the design of appropriate inlets for passive

control of rotating stall. (Presented a paper at the 1999 JPC)

Further experimental evaluations of passive control schemes for

suppression of rotating stall. (Presented a paper at the 1999 IEEE

Conference on Control Applications)

Combined the backstepping control method from the literature

with the adaptive neural net/fuzzy logic scheme for improving

robustness of the controller and evaluated the scheme in simulations.

(Presented papers at the 1999 JPC and 1999 AIAA GNC)

MITE


Schematic of experimental set up flow separators and flow recirculation l.jpg

Schematic of Experimental Set-up(Flow Separators and Flow Recirculation)

Servomotor and bleed

Bleed/recirculation loop

Computer

Main Throttle

Controller

Pressure Measurements


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Flow Separators in the Inlet

  • Moore predicted that one separator in the inlet should eliminate the rotating stall altogether (Patent No. 5,297,930 by Moore F, K. “Rotating Stall Suppression” )


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Pressure Oscillations with and without an Inlet Separator

  • The separator seems to have no apparent effect upon the traveling waves


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Effect of Eight Flow Separators on Rotating Stall Amplitude


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Effect of Flow Recirculation on Rotating Stall


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Effect of Flow Recirculation with Active Control on Rotating Stall


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Compressor Pressure Rise versus Main Throttle Opening for Different Ambient Bleed Openings


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Compressor Pressure Rise versus Normalized Flow Rate for Different Ambient Bleed Openings


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Compressor Pressure Rise versus Normalized Flow Rate for Different Recirculation Bleed Openings


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Model based controller

-

x

+

System

+

Linear

controller

Model

inversion

+

Adaptive

neural net/

fuzzy logic

School of Aerospace Engineering

Adaptive Neuro-fuzzy Controller

xc

MITE


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School of Aerospace Engineering

Adaptive Neuro-fuzzy Controllers

Hybrid control methodology which combines model

inversion with neural nets and fuzzy logic

Parameterization of uncertainty using neural nets and

fuzzy logic and adaptation of parameters based on

Lyapunov stability theory

Rule base adaptation and linear controller gain

adaptation to accommodate actuator limits

MITE


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School of Aerospace Engineering

Response to Initial Disturbance with Model

Uncertainty

Controller is based on fifth order compressor map

Simulation is based on third order compressor map

Model based controller

Hybrid controller with fixed linear controller gain

Hybrid controller with variable linear controller gain

Rotating stall amplitude

Non-dimensional time

MITE


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School of Aerospace Engineering

Related Work

T700 Engine Fuel Control Using Adaptive Neural networks

MITE


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(Feedforward

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:

Q

,

T

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r

2

u

N

PREF

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ad

Neural

1

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,

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,

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School of Aerospace Engineering

T700 Engine Fuel Controller

+

Governor

Rate

Compensation

and Dynamics

HMU

(Nonlinear

State

Feedback)

u

T700

Engine

Np

PI

-

-

+

ECU

MITE


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School of Aerospace Engineering

Performance of the T700 Engine Fuel Controller

Power

Turbine

Speed

(%)

Time (sec)

MITE


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School of Aerospace Engineering

Performance of the T700 Engine Fuel Controller to a Periodic

Load Disturbance with and without adaptive neural networks

MITE


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School of Aerospace Engineering

List of Accomplishments (Continued)

Implemented the observer scheme for on-line identification of stall

precursor waves and experimentally evaluated a novel active control

scheme based on stall precursors for active surge control in the

centrifugal compressor experimental facility at Georgia Tech.

MITE


Centrifugal compressor setup l.jpg

Centrifugal Compressor Setup

Data Acquisition

Computer

Pressure

Transducer

Pressures

Pressure Measurements

Control Variables

Throttle Valve

Inlet pressure readout

Control Computer

Self

entraining

combustor

Frequency/Amplitude Observer

servomotor

Control Law

servomotor

Fuel Valve

Throttle and Fuel

Valve Commands


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Controller Essentials

  • Utilizes real time observer that identifies the frequency and amplitude of the most dominant modes of oscillations in the inlet pressure signal

  • Sets on-off alarm signal when precursors waves are identified with strong enough amplitude

  • Varies the fuel flow rate or other actuators according to the alarm signal


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Controller Essentials (Cont.)

  • Rejecting rather than suppressing stall

  • Provides global stability

  • Does not require high bandwidth actuator

  • Can work with existing fuel injection systems

  • Requires very little information about compressor characteristics


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Real-Time Mode Observation

Low Back Pressure, 15 KRPM


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Real-Time Mode Observation

High Back Pressure Nearing Surge, 15 KRPM


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Real-Time Mode Observation

Uncontrolled Surge, 15 KRPM


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Real-Time Mode Observation

Uncontrolled Surge, 15 KRPM


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Real-Time Mode Observation

Uncontrolled Surge, 30 KRPM


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Real-Time Mode Observation

Uncontrolled Surge, 30 KRPM


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Real-Time Mode Observation

Uncontrolled Surge, 30 KRPM


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Real-Time Mode Observation

Uncontrolled Surge, 30 KRPM


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Control Using Throttle Actuation


Control using throttle actuation cont l.jpg

Control Using Throttle Actuation (Cont.)


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Control Using Fuel Valve Actuation


Control using fuel valve actuation cont l.jpg

Control Using Fuel Valve Actuation (Cont.)


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School of Aerospace Engineering

Future Work

Further theoretical, simulation (using Dr. Sankar’s

CFD models) and experimental evaluations of

control actuation schemes (e.g., bleed valve, fuel flow

modulations, etc.) using the centrifugal compressor

facility.

Experimental evaluation of novel controllers.

Further analysis of the effect of inlet parameterson

rotating stall in axial compressors.

MITE


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