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

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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

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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
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Why becomes flow actuation so attractive now?

• First experiments with flow actuation goes back
  in the 40s 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

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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
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Two Major Braches in MEMS Application in
Turbomachinery
Flow Actuation by Microsystems
Micro Turbomachines(Pumps, Gasturbines)
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)
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Vision Smart Compressor

• 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

Active Surge Control
Active Clearance Control

• Attempt
• Active Surge Control
• Active Vibration Control
• Active Clearance Control
• Using Microsystems and smart materials

Active Vibration Control
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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)

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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

Focus on Off-Design Conditions under External
Control
Altitude
Short Range vs. Long Range
Mission Time
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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
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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

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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

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6th Framework Program ADVACT

• 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
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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 Websters 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 MTU Rolls-Royce Snecma Onera IEM
N (Institut dÉlectronique de Microélectronique
et de Nanotechnologie of CNRS)
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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

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Origin Turbomachinery Flow

• 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

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

Simplified to

• 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

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Upsizing of a Compressor Working Line
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
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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

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Time Signals and Spectra _at_ Constant Throttle
Position with ASC
Sensor and Aktuator Signal 66 LPC Speed, 18
Valve Opening (Gear Factor 30, 1st Search Range)
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Time Signals and Spectra _at_ Continuous Throttling
with ASC
Sensor and Aktuator Signal 66 LPC Speed, 18
Valve Opening (Gear Factor 40, 1st Search Range)
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Air Injection Nozzles in front of a Larzac Engine
Injection Channels
Turnable Nozzles
External Air Supply
Injection Casing (view from Rotor 1 forward)
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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 _at_ 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?
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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
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Compressor Rotor Blade near Stall Condition
(simulated oil flow)
Origin of Vortex
Huge Secondary Vortex enhanced by the Tip
Clearance Leakage
High Incidence
Corner Stall
The Key Tip Clearance Flow -gt determine
Efficiency and Stall Margin
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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)
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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

Rossow (DLR)

• Method applicable as a Virtual Inlet Guide Vane
  (VIGV) in turbo machines
• Typical HPC chord 1 in (25 mm) -gt Flap 1 -gt
  0.01 in (250 µm)

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Sub-layer vortex generators
vortex system generated downstream enhances the
energy transport from the outer flow into the
near-wall regions and energises the boundary
layer
Bauer, EADS
AVT-111 Liu (Texas)
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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)
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Whats New within ADVACT?

• 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

• 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

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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
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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
• Whats about DNS / LES / DES?
• Simplification thinkable?

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Simulation Techniques Continuums Mechanics
still valid?

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

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 !
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Characteristic Values
Ratio of mean free path to length scale of the
flowNavier-Stokes with slip or non-slip
conditions at the wall
Knudsen Number
Ratio of mean molecular spacing to diameter of
typical gas moleculesgtgt 1 diluted gas
Ratio of velocity to speed of soundsub- / trans-
/ supersonic flow
Mach Number
Ratio of initial forces to viscous forceslaminar
/ transient / turbulent
Reynolds Number
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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
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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

Mainf0.1 Re 106
measured
Synthetic Jet Detail
k-e
SST
RNG
k-w
BSL
SSG
Jet Slot Width 0.5 Chord Length
Reattachment Point
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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)

Details accurately reproduced
Orkwis
Steady w/ LDSTs
Time-averaged and Steady-StateLDST Solutions
90 SJ
Time-average
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Thank You For Your Attention
Questions?