New Flow Actuation Concepts to be Studied Within European Technology Program ADVACT

New Flow Actuation Concepts to be Studied Within European Technology Program ADVACT

AVT - 128

RTO-Meeting

Prague, October 4 – 7, 2004

Dr. Sven-J. Hiller MTU Aero Engine Munich

RTO-AVT-128 Meeting, Prague, Oct 4-7, 2004Dr. Sven-J. Hiller (MTU Aero Engine) 2 - 36

Contents

Status and Motivation for the Link between Fluid Mechanics and Microsystems

6th Framework Program ADVACT

Flow Actuation Concepts – Examples

Numerical Simulation Issues and Examples


Why becomes flow actuation so attractive now?

• First experiments with flow actuation goes back in the 40’s of the last century

Pulsed hot wire triggers instability waves

• Growing interests in flow control due to wider knowledge about the flow physics

• Achievement in e.g. efficiency growth on the traditional design way is limited by the amount of effort necessary (time and costs) and uncertainties (manufacturing)

• Recent achievements in simulation technique, control science (growing computer capabilities, more efficient control algorithm, embedded systems) promise new ways for further efficiency growth and better operability, e.g. control loops with feedback


Comparing Aero Engine Industry with Automotive Industry

• Electronic Microsystems widely used in modern cars

• Premium class cars equipped with ~ 3.5 km (2 miles) wiring

• Minor usage of Microsystems in Aero Engines

• Some of the reasons may be:• Lower number of pieces• Harsh environment• Reliability• less experiences with Microsystems• high level of optimal designs already

achieved (i.e. efficiency, life cycles)

Expecting a change in the Aero Engine Industry in mid-term time frame


Two Major Braches in MEMS Application in Turbomachinery

Micro Turbomachines(Pumps, Gasturbines)

Flow Actuation by Microsystems

Autarkic Energy Supplierdue to their high energy density(replacement of conventional batteries)

Very Local Flow interaction

Active Energy Conversion with the fluid enables the establishing of control loops

Benefits: Size, Weight

Benefits: Size, Weight, Control Loops

Step on the way towards a clever, fully controlled engine

Kang et al. (2003)(Stanford)

Frechette et al. (2000) (MIT)


Active Surge Control

Active Vibration Control

Active Clearance Control

Objectives:• Increase in Efficiency by better use of

design space in aerodynamics • Surge Margin• Blade Vibration

• Increase in efficiency by reduced clearances

• Reduction in cost and weight by reduced number of parts

Attempt:• Active Surge Control • Active Vibration Control • Active Clearance ControlUsing Microsystems and smart materials

Attempt:• Active Surge Control • Active Vibration Control • Active Clearance ControlUsing Microsystems and smart materials

Vision: Smart Compressor


Ambition for modern flow control concepts

• Modern aero engines already achieved a high level of efficiency (based on huge experience basis)

• Further significant increase is a question of benefit / requirements vs. effort

• Regulation and Laws (environmental impact (noise, pollution), taxes)

• Cost (development, manufacturing, maintenance)

• Cost (operation, end-user)

• But: all the statements base on a single “Working / Design / Warranty Point” consideration

• Reality is a broad spectra of “Working Points”, ”Power Settings”, etc.

• Many different “Off-Design” Conditions (e.g. short range air transportation)


Consequences

• The “Time Integral” is the amount of energy used to achieve a certain condition, location etc.

• A better performance outside the “Design Point” has the potential to reduce the total amount of energy required

• Improvement of the so-called “Off-Design Performance” (will also increase the Design Performance as well) promise an energy saving in general

Alti

tude

Mission Time

Short Range vs. Long Range

Focus on “Off-Design” Conditions under External Control


Contents

Status and Motivation for the Link between Fluid Mechanics and Microsystems





Attractiveness of Microsystems for Flow Actuation (locally)

• Laws of the Fluid Mechanics are highly non-linear (sometimes chaotic)

• Small change at one side can causes significant change on the other side

• Urgent need to find the most efficient flow scenarios

• Boundary Layer Flow (see also AVT-111)

• Flow Separation and Reattachment

• Transition (onset and delay)

• Unstable Flow (Bifurcation)

• Buoyancy-driven Flow


Attractiveness of Microsystems for Complex Flow Scenarios

• Sensitive Flow Scenarios

• Shock location

• Shock – Boundary Layer Interaction

• Vortex-dominate Flow

• Wing-Tip Vortex (Delta-Wing, etc.)

• Noise and Acoustics

• Aero acoustics

• Instabilities (burner instabilities, etc.)

• Bifurcation of the Complex Flow Scenarios

• Flow at Adverse Pressure Gradient (Dynamic Stall, etc.)

• Compressor Surge and Stall



• EC launched within the 6th Framework the research project ADVACT “Development of ADVanced ACTuation Concepts to Provide a Step Change in Technology Used in Future Aero-Engine Control Systems”

• Joint Research Program of Industrial Partners and Universities

• Runs 48 month from July 2004 to June 2008

Rolls-Royce plc Industria Birmingham University

MTU Aero Engines VKI Sheffield University

Snecma Moteurs ONERA TU Dresden

Avio CNRS INSA

Turbomeca Cambridge University Politecnico di Torino

DaimlerChrysler AG Cranfield University


Main Objectives

• “… generic study of the benefits of expanded actuation capabilities couples to development of specific technology which will show the capabilities for identified applications. “

• 9 Work Packages (see John Webster’s Presentation)

• Focus on WP 2 “MEMS Development and Cascade Airflow Control” (Lead: MTU)

• Close link to WP 3 “Boundary Layer Control in Intake and Ducts” (Lead: Snecma)

Partners in WP2: MTURolls-RoyceSnecmaOneraIEMN (Institut d’Électronique de Microélectronique et de Nanotechnologie of CNRS)


Compressor Stability

Flow effects involved

• Flow Separation at the blade surface during Off-Design (Airfoil Stall)

• Induced Flow Separation through 3D Tip Clearance Flow

• Boundary Layer-Shock interaction, especially in the tip gap region of the rotor blade

• Unstable Flow Regime when throttled (Stall & Surge)

• Instabilities inside the flow (rotating and non-rotating instabilities)

• Vortex-dominate Flow (Secondary Vortex / Passage Vortex)

• Corner Stall


Origin: Turbomachinery Flow

• Compressor Flow (rotating)• Off-Design Conditions• Compressor Stall & Surge• Tip Clearance Flow

Simplified to• Cascade Flow (non-rotating)• Gap between Blade and (non-moving) Casing• Cold Conditions (Temperature less than any critical temperature for a actuator device)• Size in the order of 0.1% …1% of a typical HPC Blade Chord (20 µm … 200 µm)• Lab-Scale Demo Test

• information about the flow mechanism involved (Lab-Scale)• information concerning reliability, certification, etc.• concepts for possible control loops• adequate numerical simulation techniques• development of MEMS technology for actuators


Upsizing of a Compressor Working Line

Surge Margin

Eff

icie

ncy

PG = -10%

= +2%

Pre

ssur

e R

atio

Mass Flow Rate

Larger Power DensityHigher Thrust-Weight-Ratio

Upsizing of the Working Line toward the Efficiency Optimum

Upsizing of the Working Line enables a significant improvement of the Power Density and Efficiency based on a modified Compressor Design Concept

The compressor runs stabilised with a lower surge margin but higher efficiency


Joint Research Project Between MTU, University of Armed Forces Munich and Engineering Office for Thermoacoustics (IfTA)

• Objective were:

• to identify some precursors of the LP compressor surge

• to stabilize the LP compressor by air injection into the tip region of the Rotor 1

• Development of a controller device which detects the precursors and reacts on them (Active Surge Control)

• Test vehicle: Larzac 04 Engine installed at the University


Time Signals and Spectra @ Constant Throttle Position with ASC

15.65 15.66 15.67 15.68 15.69 15.7 15.71 15.72 15.73 15.74 15.75

-10

-5

0

5

10

LVDTs 1,3,5,7,9 und Kulites 1-5 (von oben nach unten), File352

Time [s]

Akt

uat

or

Sen

sor

Opening of the Valve andStart of the Control Loop

Sensor and Aktuator Signal66% LPC Speed, 18% Valve Opening (Gear Factor = 30, 1st Search Range)


Time Signals and Spectra @ Continuous Throttling with ASC

7.86 7.88 7.9 7.92 7.94 7.96 7.98 8 8.02

LVDTs 1,3,5,7,9 und Kulites 1-5 (von oben nach unten), File356

Time [s]

Akt

uat

or

Sen

sor

Sensor and Aktuator Signal66% LPC Speed, 18% Valve Opening (Gear Factor = 40, 1st Search Range)


Air Injection Nozzles in front of a Larzac Engine

Turnable Nozzles

External Air Supply

Injection Channels

Injection Casing (view from Rotor 1 forward)


Air Injection

• Comparable results from different research groups• all experiments base on discreet air injection equally spaced around the circumference• Typically ~12 air injectors at the circumference used

Injected Air

as % of CoreMass Flow

Reduced Core Mass Flow @ Stall

Scheidler et al.

(Uni Armed Forces, MTU)

Larzac Engine 2 Stage - LPC, High Speed

5 % ~ - 9 %

Weigl et al.(MIT)

Compressor Rig

Single StageHigh Speed

3.6 % ~ - 11%

Nie et al.

(Chinese Academy)

Compressor Rig

3 Stage, Low Speed

0.056% ~ - 5.8 %

Question: Can the Injection Mass Flow further reduced by a huge number of Micro Actuators?


Contents

Status and Motivation for the link between Fluid Mechanics and Microsystems





Compressor Rotor Blade near Stall Condition (simulated oil flow)

High Incidence

Huge Secondary Vortex enhanced by the Tip Clearance Leakage

Corner Stall

Origin of Vortex

The Key: Tip Clearance Flow -> determine Efficiency and Stall Margin


Adaptive Blade Shape

• Control of Curvature means Control of Stall Onset (in certain limits)

• 4 Options (mechanical)• Nose-Dropping Devices (DLR -

Geissler/Trenker)• Actuated Flaps at Suction Side / Trailing Edge

(ONERA, CEDRAT) (e.g. piezoactuators)• Shape Adaptive Airfoil (TU Kassel –

Müller/Lawerenz, segmented airfoil)• Local Thickness Change by surface mounted

devices • “Flexible” Blade Shape (fluidic, e.g. aspirated /

transpired airfoil) in order to delay dynamic stall

AVT-111 Chandrasekhara (NASA Ames)AVT-111 Glezer (Georgia Tec)


MiniTED = Miniature Trailing Edge Devices

• Very small high-lift devices attached at the trailing edge of an airfoil

• Co-operation between DLR (Institute for Aerodynamics Braunschweig) and Airbus

• Transsonic and high Reynolds Number Flow

• Method applicable as a Virtual Inlet Guide Vane (VIGV) in turbo machines

• Typical HPC chord 1 in (~25 mm) -> Flap 1% -> 0.01 in (250 µm)

Rossow (DLR)


Sub-layer vortex generators

Bauer, EADS

vortex system generated downstream enhances the energy transport from the outer flow into the near-wall regions and energises the boundary layer

AVT-111 Liu (Texas)


Aerodynamic Airfoil Shape Change

Controlled Link between Pressure and Suction Side

Synthetic Jets Array used for “virtual” airfoil shape change (aspirated / transpired airfoil)

AVT-111 Glezer (Georgia Tec)


What’s New within ADVACT?

• bring the effects into a turbo machine environment, e.g. internal aerodynamics

• assessment of the various effects in an unsteady rotor-stator environment

• assessment of the additional requirements concerning certification, reliability, aging, design and maintenance of an aero engine

• many effects are known • some are well understood, other partially• mainly developed with the background of external (wing) or pure aerodynamics (flat plate)

Our Objective


Contents

Status and Motivation for the link between Fluid Mechanics and Microsystems





Simulation Techniques Issues

• Domains simulated embodies very different length scales

• because of smooth mesh coarsening from the actuator to the airfoil the mesh sizes tend to be very large

• Some Questions to be answered:

• Continuums Mechanics still valid?

• Role of Turbulence Models (URANS) and Wall Treatments

• What’s about DNS / LES / DES?

• Simplification thinkable?


Simulation Techniques – Continuums Mechanics still valid?

• Stationary statistics (large number of molecules) and continuity of transport quantities (viscosity and diffusivity) must be valid

• Assumption:

meassured cube theofLength Side -

Mass Molecule -

Molecules ofNumber -

Density -

*3

L

m

N

L

mN

For Air: Lgas = 1 µm (10-6 m)

For simulation domains with edges larger then 1 µm the application of Navier-Stokes-based solvers (e.g. standard (U)RANS CFD solvers) are still valid !


Characteristic Values

L

Kn

d

Knudsen NumberRatio of mean free path to length scale of the flowNavier-Stokes with slip or non-slip conditions at the wall

Ratio of mean molecular spacing to diameter of typical gas molecules>> 1 diluted gas

a

cMa

Ratio of velocity to speed of soundsub- / trans- / supersonic flow

Lc *

Re Ratio of initial forces to viscous forceslaminar / transient / turbulent

Mach Number

Reynolds Number


NASA Test Cases (2003)

• NASA Langley initiated and published 3 test cases for flow actuators and flow actuation for CFD validation

• Case 1: Synthetic Jet into Quiescent Air

• Case 2: Synthetic Jet in a Crossflow

• Case 3: Flow over a Hump Model (Actuator Control)

Wall-mounted Glauert-Goldschmied type body

Slot across span

http://cfdval2004.larc.nasa.gov/case1.html




CFD Validation for Case 3 (Förster, Hiller)

• Usage of in-house and commercial solver (in the frame of a diploma thesis)

• Aim: meet the measured re-attachment point of the separated hump flow

• Assessment of the effects of a Synthetic Jet onto the main flow

Synthetic Jet Detail k- k-BSL SST RNG SSGmeasured

Reattachment PointJet Slot Width ~ 0.5% Chord Length

Mainf=0.1Re ~ 106


Simplification (proposed by Orkwis (Connecticut))

• The effect of a Synthetic Jet onto the main flow will be simulated as a special kind of momentum sources rather then the detailed flow interaction between the jet and the main flow

• Pro: still working on the “coarser” main flow mesh with short turn-around times

• Cons: a huge calibration task is necessary in advance (database-like)

Time-averaged and Steady-State+LDST Solutions: 90˚ SJ

Time-average

Steady w/ LDSTs

Details accurately reproduced

Orkwis

New Flow Actuation Concepts to be Studied Within European Technology Program ADVACT

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