passive flow control on civil aircraft flaps using sub-boundary layer

KATnet II Separation Control Workshop - 01-03 April 2008

AWIATOR Project Perspectives:Passive Flow Control on Civil Aircraft Flaps using

Sub-Boundary Layer Vortex GeneratorsDavid Sawyers

Aerodynamics R&T Co-ordinatorAirbus UK Limited

No SBVGs With SBVGs

KATnet II Separation Control Workshop - 01-03 April 2008 © A

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Presentation Overview

• Background�Passive Flow Control for High Lift Applications �What are SBVGs and how do they work?�Potential Benefits of using SBVGs on Trailing Edge Flaps �Previous Work on SBVG design

• SBVGs in the AWIATOR Programme�SBVG Design�Wind Tunnel Testing�Flight Testing�Concluding Remarks

KA

Tnet II Separation C

ontrol Workshop -01-03 A

pril 2008P

age 3

© AIRBUS UK LTD. All rights reserved. Confidential and proprietary document. Background


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Passive Flow Control for High Lift Applications

• Motivation�Extended ranges for civil aircraft means that the take-off and

landing performance (low speed) is a critical factor in design.• Conventional ways to Improve Low Speed Performance

�Increase the wing area (potentially increased drag & reduced range).

�Design a more mechanically complex high-lift system (increased weight).


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Passive Flow Control for High Lift Applications

• The use of Simple (Passive) Flow Control Devices�Increases the efficiency of high lift systems whilst maintaining

simplicity.

• High lift performance is limited by boundary layer separations. �Two approaches to reduce separation:

– (1) careful optimisation of flap gap (� increased gap sensitivity, more difficult to manufacture within tolerances)

– (2) limit flap angle (� loss in potential performance CLmax)

�Sub Boundary-layer Vortex Generators (SBVGs):– (1) Reduce flow sensitivity to flap gap.– (2) Re-attach separated flow for high flap angles without incurring a

large drag penalty at cruise and take-off.


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SBVGs

• What are they?�Surface mounted vortex generators where the VG height < BL height

• How they work?�These SBVG’s control the flap boundary layer by adding momentum to the

boundary layer, at the flap surface. �By doing so SBVG’s control (delay) the boundary layer separation. �These SBVGs are mounted on the flap upper surface so that they delay

flap boundary layer separation only when the flap is deployed. – When the flap is stowed, the SBVG’s are contained in the cove region, under

the shroud.

Vortex Influence Paths

SBVG on Flap

Direction of onset flow

h


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Potential Benefits of SBVGs on Flaps

• Existing Aircraft Application (i.e. as a retrofit)�Increase CL

– At high flap angles the flap becomes separated but SBVGs can re-attach the flap and allow the a/c to cash in the benefit of increased lift from the increased flap angle.

• potential to decrease approach speed and hence approach noise

�Decrease Sensitivity to Gap (risk mitigation)– Can be used at take-off or landing to reduce

separations due to flap gap geometry sensitivity.

�Increase Drag at Landing– Increasing the flap angle will have a drag

increase without any loss in CL max which may be favourable in cases where the option of a steep approach would be beneficial.

Higher flap angle

With SBVGs

CL

D

CL

D


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Potential Benefits of SBVGs on Flaps

• New Aircraft Design �New a/c variant that requires higher CL, can use SBVGs to achieve

higher flap angles without having to go to a complex system�Design a simplified high lift system with a smaller flap at higher

angles (reduce weight and complexity) but give the same landing and take-off performance.


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Previous Work

• National High-Lift research programmes with Airbus & QinetiQexamined SBVG designs (shape, size, angle) in a simple 2D BL test. (CARAD)

• Looked at different SBVG designs and their effectiveness for more complex applications. (NEXUS)

Full complex configuration, at high Re No. (6m) (2001)

0

5

10

15

x/h

-2000.00 -1595.96 -1191.92 -787.88 -383.84 20.20

Boundary-layer Testing


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SBVGs in AWIATOR


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SBVGs in AWIATOR

• AWIATOR (Aircraft WIng with Advanced Technology OpeRation) �The aim of this project was to contribute to new future aircraft designs by

applying and integrating new technologies. (CEC FP5)�Demonstration by various flight tests on an A340 after having first been

simulated using a number of computational methods and validated in wind tunnel and other aircraft ground tests.

• Objectives of SBVG task (T3.4)�To demonstrate technologies for improving the performance of trailing

edge flap systems using simple flow control devices.�To demonstrate if SBVGs can be used to:

– increase the trailing edge flap angle 32° to 35°– by doing this increase CL throughout the incidence range without incurring a

loss in L/D for take-off.• Phases

�Phase 1: SBVG Design�Phase 2: Wind Tunnel Testing�Phase 3: Flight Testing


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SBVG Design

• CFD study (ONERA)�Structured mesh �Navier-Stokes calculations (elsA code) �Data on the sensitivity of the flap boundary layer to

Reynolds Number. �Experimental pressure data was used to validate

the CFD for the baseline and finally complex CFD calculations with SBVG representation was also used to refine the final SBVG design.

• BL Calc (QQ)�Using the CFD calculations as an input boundary

layer calculations were performed �CALLISTO code �Scaled SBVGs for the boundary layer of the

aircraft. • Output

�The output of this collaborated design work was a baseline array of SBVGs, which was taken forward to be optimised and demonstrated in a series of wind tunnel tests.

CFD

F1 Wind Tunnel Test

CFDCFD

F1 Wind Tunnel Test


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Wind Tunnel Testing


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Wind Tunnel Testing Overview

• Model�A340 high-lift half model

– Model scale 1:14.4

• Tunnel Entries�Entry 1: Airbus LS Tunnel, Filton

– June 2004– Atmospheric (Re=2.2m)– ID optimum SBVG arrangement

�Entry 2: ONERA F1 Tunnel– July 2004– Pressurised to 3bar (Re=6.6m)– Examine Re effects

• Measurements�Forces & Oil flow visualisations


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Wind Tunnel Testing – Airbus FLSWT Test

• Objective: �To assist in determining the optimum SBVG arrangement to be

fitted to the flaps for the AWIATOR test flight to allow an increased trailing edge flap deflection angle with acceptable flow quality.

• Main Observations:�The optimised SBVG array significantly reduced the extent of

boundary layer separation of the flap at an increased flap deflection of Gf = 35°.

�The addition of SBVGs to the flap at Gf = 35° deflection increased the lift coefficient by up to 2.2% over a wide incidence range compared to the baseline configuration of Gf = 32° without SBVGs.

�The effect of SBVGs at a fixed landing flap deflection increased the lift coefficient by 'CL = 0.01 to 0.04 over part of the incidence range indicating, as expected, that the vast majority of the lift increase is due to increase in flap angle.

�A trend to a small increase in drag of 4 counts (Cd=0.0004) in take-off configuration is within the repeatability of the wind tunnelbalance and therefore deemed not significant.


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Wind Tunnel Testing – Airbus FLSWT Results

No SBVGsNo SBVGs No SBVGs

With SBVGsWith SBVGs

With SBVGs


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Wind Tunnel Testing – ONERA F1 Test

• Objective:�To investigate Reynolds number effects on the optimised SBVG array as defined in

the Airbus LSWT test (Filton). • Main Observations:

�Good correspondence of CL-alpha curves and drag increments was observed between FLSWT and F1.

�At high Reynolds number (Re=6.6m) the optimised SBVG array from the Filton test (ref height of h1) significantly reduced the extent of boundary layer separation of the flap at an increased flap deflection of Gf = 35°, see Figure.

�With an increase in Re the incidence range of CL improvements due to higher flap deflection and SBVG application is extended, see Figure.

�At Re=6.6 the level of CL improvement at a reference alpha (approx 0.8 CLmax SBVGs off) is slightly larger (2.25%) than at atmospheric conditions (Re=2.2m)

�SBVGs of smaller heights (h2 and h3) could not cure flap flow separation at the highest Reynolds number.

�With higher Reynolds numbers a drag increase in take-off configuration due to SBVGs installation at atmospheric pressure is not observed outside the tolerance of the balance.


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Wind Tunnel Testing – ONERA F1 Results

No SBVGs

With SBVGs

No SBVGs

With SBVGs

No SBVGs

With SBVGs

No SBVGs

With SBVGs


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Wind Tunnel Testing – ONERA F1 Results

AWIATOR 3.4 SBVG LSWT TestModell 419B, G s =19.6°/23°/23°, G f=32°, 35°

Ma=0.2, Re=2.2x10 6 , 6.6x10 6

X:\A erodynamic s\B61\HLWD\K arsten\AWIATOR\Onera F1\OneraF1_FLSWT_forces_prel_datasorted_0721z.exy SB VG Improvement Po tenti al DCLa V2

Run 865, df=35°, Re=2.2E6, SR1optRun 591, df=35°, Re=6.6E6, SR1opt

Reference DataRun 524, df=32°, Re=2.2E6, no SBVGsRun 702, df=32°, Re=6.6E6, no SBVGs

Increase in CL of 2.25% at ref alpha

Gf=32q no SBVGs

Del

ta C

L

Gf=35q with SBVGs (Re=6.6m)

Gf=35q with SBVGs (Re=2.2m)

Alpha


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Flight Testing


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Flight Testing - Overview

• Main Objective:�To demonstrate, on a full scale-aircraft, that SBVGs can be used to increase the

trailing edge flap angle beyond the current maximum whilst maintaining attached flow.�This would release an additional lift increment whilst minimising any increase in

buffeting. • Tests Completed:

�The optimised SBVG arrangement as identified from wind tunnel testing was tested at aircraft scale on the A340-300 MSN 1 flight test aircraft.

�The aircraft was tested at stall and climb performance conditions with and without SBVGs installed to allow a full comparison of results.


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Flight Testing – Aircraft Modifications

• Modification of the flap kinematics • Mechanism changes to allow flaps to

deploy to 35°�New rear links as detailed Flap

System�Adaptor wire installed on MSN1 �Spoiler extension on spoilers 3-5

• Mounting of SBVGs on the flaps�Design & Manufacture

– SBVGs cut out of aluminium strips

�Mounting of SBVGs – Strips mounted across full span of

I/B & O/B flap– Mounted using speed tape


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Flight Testing – Flight Test Instrumentation

• Flight Test Instrumentation• Lift and drag measurements (Onboard)

• Pressure measurements�Slat-wing-flap (1 station)�Flap (additional station)

• Flap deformation measurements (EDT)�2 stations with stereo arrangement

(DLR)

• Flow cones & cameras�On the slats 3/4, wing & flap

• Indication of Tail Plane buffeting �Accelerometer mounted on HTP

wing pressure measurement

flap deformation measurement (EDT)

wing pressure measurement

flap deformation measurement (EDT)flap deformation measurement (EDT)


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Flight Testing – Main Observations

• Flap Flow Behaviour�Flow cones indicated improvement in flap flow

with SBVGs on at 35°.�Flap flow at 35° without SBVGs was not as

separated in 2005 as expected from previous experience.

�The flow behaviour observed on the wing with the SBVGs installed was more noticeably improved for the flap at 35° than with the flap at 32°.

�At 35° there is no clear improvement on the inboard flap as it remains largely separated. On the outboard flap there is improvement whatever alpha.

• CL-Alpha Plots�32-35 CL-alpha trend is as expected, increase in

CL of approx 2.5% at reference alpha.�CL increase across the range but 35° stall is 0.3

degree early.


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Concluding Remarks

• This work has demonstrated, at aircraft scale, that by reducing flap flow separation SBVGs can be used to enable low speed improvements associated with increased flap angle to be exploited on civil aircraft.

• The increase in flap angle leads to an increase in lift that can be exploited in landing across the CL range without incurring a significant drag penalty in take-off.

• SBVGs provide a simple, effective, innovative means of enabling the increase of the performance of an existing under-performing flap system with imposing any significant weight, complexity, cost penalty.

• SBVGs have the future potential to adopt a simpler, lighter, cheaper flap system to give a similar performance by exploiting the following characteristics: �Same lift despite non-optimum flap gap geometry �Allow an increase in the maximum flap deployment angle


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…any Questions?

Thanks…


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4/5/2008 Page 27

© AIRBUS UK LTD. All rights reserved. Confidential and proprietary document.

This document and all information contained herein is the sole property of AIRBUS UK LTD. No intellectual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS UK LTD. This document and its content shall not be used for any purpose other than that for which it is supplied.

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passive flow control on civil aircraft flaps using sub-boundary layer

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