TELFONA,Contribution to Laminar Wing Development

for Future Transport Aircraft

K. H. HorstmannAeronautical Days, Vienna, 19th - 21st June 2006

Content

Motivation

Determination of transition

Objectives and structure of TELFONA

Actual status

- Pathfinder model design

- Receptivity test preparation

Outlook

Drag reduction by laminar flow technology

More than half of the aircraft drag is caused by friction

Thus laminar flow technology has a high potential of drag reduction

Example A 340 (HLFC):

Wing: -12%Empenage -3%Nacelles: -1%

Potential of NLF is even higher but- restricted to smaller aircraft- and lower leading edge sweep angle

Problem for A/C development:- Prediction of transition (aircraft performance) not sufficiently reliable- Experimental validation even less reliable

Prediction of laminar-turbulent transition

N

0

eAA

=

0AAlnN =

„N-Faktor“

Transitions-criterion:

• Boundary layer analysis for given pressure distribution

• Stability analysis of boundary layer, Orr-Sommerfeld-eq. (local, incom-pressible, SALLY, COAST, LILO)

• Determination of N-factor envelope from stability analysis

• Use of critical N-factor for TS or CF instability (empirically determined) for transition prediction

Location of neutral stability

Envelope of stability analysis

Predicted transition location

Nlimit

Limit N-Factors for flight and wind tunnel conditions

NLF und HLF in S1Ma

Stability analysis:• local, incompressible

•SALLY, COAST, LILO

•TSI in local flow direction

•CFI for f=0 Hz

NLF and HLF N-Factors substantially lower in wind tunnel than in flight

No critical N-factor data for ETW available

Objective of TELFONA:

ability to reliably predict NLF aircraft performance in flight based on wind tunnel tests and CFD results

by:

• Calibration of the ETW facility for testing laminar flow aircraft- Design and test a pathfinder wing- Determine transition inducing N-factors

• Integration of receptivity modeling into transition prediction methods- Understand and integrate effects of noise and turbulence in transition pred.

• Flight performance prediction methods for a laminar flow aircraft- Investigate scaling methods for flight performance prediction

• Validation of developed methods- Design and test a Performance wing (HARLS-wing)- Evaluate wind tunnel test results and prediction based on pathfinder data- Scale to flight performance

Structure and work flow of TELFONA

Pathfindermodel

Performancewing

WP

0:M

anag

emen

t, di

ssem

inat

ion,

exp

loita

tion Aerodynamic

wing designAerodynamic wing design

WP 1: Design

Development & Manufacture

WP 2: Manufacture Development & Manufacture

Validation ofscaling appr.

Performancescaling meth.

WP 5: performance prediction

ETWTests

ETWTestsWP 3: Tests HLFC

Tests

Testevaluation

N-factorcalculation

WP 4: Testsevaluation

Receptivitymodelling

Stabilitymethods

Design objectives of the Pathfinder wing

• Design Mach number of 0.78

• Total Mach number range to be covered at least from 0.70 to 0.78.

• Design Reynolds number: 20 Million

• Leading-edge sweep angle of 18°

• Taper ratio approximately 0.8

• Upper surface:- should have linear envelope of TS N-factors

at design Mach number

• Lower surface:- should have linear envelope of CF N-factors

at design Mach number

• N-factor envelopes (obtained with linear local stability theory for incompressible media) should have the following extend:

• NTS: 6 to 10• NCF: 5 to 8

• Isobars should be close to constant chord lines between about 30 and 70% of span

N

x/c0.5

10

5

Pathfinder Wing Design

Airfoil design

• CFD infinite swept wing design

• Laminar B/L analysis

• Stability analysis

• Transition criterionCIRA

ONERA

DLR

3D Pathfinder Wing Design

Geometrical Data of Pathfinder Wing Model

3D Pathfinder Wing Design

Parallel isobar design on upper and lower surface of pathfinder wing model (with fuselage and belly fairing)

Upper Surface Lower SurfaceUpper Surface Lower Surface

30% of span

70% of span

Fully inverse Design

3D Pathfinder Wing Design

Pressure distributions of pathfinder wing model between 0.3 and 0.6 of span for different lift coefficients and Mach numbers

x

p

0 0.2 0.4 0.6

-1

-0.8

-0.6

-0.4

-0.2

0

0.300< eta<0.6CL=0.2163

M=0.76

M=0.78

M=0.80

x

cp

0 0.2 0.4 0.6

-1

-0.8

-0.6

-0.4

-0.2

0

0.300< eta<0.6M=0.78

CL=0.099

CL=0.2163

CL=0.3343

M SweepcL Sweep

3D Pathfinder Wing Design

Isobar evolution at upper surface of pathfinder wing model at design conditions with four degree yaw angle

3D Pathfinder Wing Design

Pressure Distributions of Pathfinder Wing at Design Conditions with four Degree Yaw Angle

M= 0.78β=4o

Rec=20 mill.cL= 0.2174

x/c

c p

0 0.2 0.4 0.6

-1

-0.8

-0.6

-0.4

-0.2

0

0.300< η<0.6M=0.78, CL=0.2163 (β=0o)

β=4o (right wing)

β=0o

β=4o (left wing)

3D Pathfinder Wing Design

Pathfinder configuration with wing, fuselage and belly fairing

WP 1.1: 3D Pathfinder Wing Design, DLR

Details of the Pathfinder Configuration

B/L receptivity investigationPreparation of test in PETW with different turbulence and noise levels:

•Modification of turbulence level by additional grids in PETW

•Measurement of free stream turbulence, noise and pressure fluctuations

•NLF airfoil for M=0.78 and Re=8.3 Mio

•Measurement of surface sheer stress fluctuations

- Very high disturbance frequencies of TS waves up to more than 100 kHz

- Very short wave lengths below 2 mm

- Standard sensors not applicable

- Use of Piezo sensors

•Modification of TS waves show B/L receptivity

Outlook (I)

Expected results of TELFONA:

• Experience in the laminar wing design process

• Validation of CFD methods for laminar flow technology

• Validation of wind tunnel testing (ETW) of laminar flow wing (NLF)

• Reliable scaling method(s) for wind tunnel to flight extrapolation

• Knowledge of receptivity of B/L for noise and turbulence

• Knowledge of performance of NLF HARLS wing

• TELFONA results are also applicable on laminar nacelle

Outlook (II)

What is missing for application of NLF for transport A/C:

• Anti-contamination systems:- Only fluid anti-contamination systems successfully tested (HYLTEC)- Fluid systems can not be combined with bleed air anti-icing- Strong need for self-cleaning leading edge surface (Lotus flower-effect)

• Anti-icing system:- Fluid systems work as de-icing systems very reliable (HYLTEC)- For bleed air anti-icing self-cleaning surface necessary

• No operational knowledge for high Reynolds number wing