Delft, September 10, 2015

Presenter:

Clyde Warsop (BAE Systems))

FIRST WORKSHOP (2) - Practical Active Flow Control Technologies: Aspirations and Realities

PRACTICAL ACTIVE FLOW CONTROL

TECHNOLOGIES: ASPIRATIONS AND

REALITIES

September 2015 2

Presentation Outline

Flow separation control has been one focus of aerodynamic research

for over a century but particularly within the last couple of decades with

the advent of new technology.

This presentation overviews some of this recent research with a

particular emphasis on my involvement/experiences over the past 2

decades

• Why flow separation control is important

• Overview developments leading to AFLoNext research activities

• Emphasize non-aerodynamic aspects

• Provide some thoughts for future direction

Some Drivers for Flow Control Research

Some Needs For Tomorrow

• Reduced Weight

• Reduced Airframe Noise

• Reduced Field Length

• Increased Payload

• Reduced Fuel Burn

Aero Design Challenges

• Increased Lift

• Simpler High Lift Systems

• More Effective High Lift Systems

• Improved Propulsion Systems

• Intake Separation Control

• Fan/Compressor Surge/Stall

Recent Enablers

Fluid dynamics knowledge

• unsteady/viscous flows - advances in simulation and measurement

Manufacturing

• MEMS, lasers, Direct Write.

• Materials technologies - Piezo & SMA’s

Control systems

• Adaptive control, Neural networks, fuzzy logic

Major European Programmes Having a Flow Separation Control Element

1995 2000 2005 2010 2015

AEROMEMS

AEROMEMS

II

AVERT

Awiator

Clean Sky

AEROMEMS: Feasibility of sub-boundary layer scale actuation

Pulsed excitation of separated shear

layers to excite secondary instability

Streamwise

vorticity

generation

Discrete, micro-scale excitation

of near-wall turbulence generation

Images: tobias.hoell; tu-berlin

Sub-BL Flow Separation

Control (Pulsed jets)

Application to

High Lift,

Intakes, Fans

compressors

High Re Demonstrations

AEROMEMS II Overview – Industrial Scale demonstrations (1998 -200

MEMS

Sensors/Actuators

Pulsed jet, 100 - 200 m/s5-20% duty cycle

200mm dia

PZT cantilever actuator50-80mm displacement

1 - 2 KHz frequency

3mm

Pressurisedsupply (30-80 kPa)

Distortion coeff. DC60 reduced

40% (0.05% engine mass flow)

MThroat =0.6

Unactuated Actuated

Surge margin increased 10% (<1%

engine mass flow)

0

5

10

15

20

0 0.5 1 1.5

Injected mass flow/compressor mass flow (%)

su

rge

Ma

rgin

in

cre

as

e

(%)

Intake Distortion and Compressor Surge

Flow Separation delayed from 30% to 90% off flap chord

Flap TE

Flap LE Separation

Separation

Flap TE

Flap LE

URANS Simulation URANS Simulation

Unactuated Actuated

High Reynolds Number Demonstrations

Key Issues to successful implementation

11

Integration with airframe

• Space often constrained

• Structural integrity/flexibility

• Power and pneumatic supplies

• EM Compatibility

• Maintenance

• Reliability/fail safe

Environmental robustness

• Rain/hail erosion, Icing, Salt water,

Humidity/temperature extremes, Lightning strike,

Fluid contaminants

Certification process is not set up to deal with

flow control systems

• Massively parallel flow control actuation systems

• configuration warning problem

Commercial considerations dictate that dispatch reliability must be very high

For an aircraft designed to use separation control to full advantage, low speed performance will be compromised with flow control inactive

Dispatch reliability must be at least as good as for passive high lift system • Failure will restrict field performance

• Design compromise between achievable dispatch reliability and potential performance improvement benefits?

AFLoNext is making a start but more attention needs to be paid to the engineering integration

Commercial Considerations

Some observations

Trend is for flow separation control to be explored for

application at wing leading edges:

• This appears to be driving requirements for pneumatic devices

towards • Higher blowing momentum coefficients

• Increasingly higher blowing velocities

• larger circular holes or continuous slots

• Increasingly high exist mass flows

• Much of our actuation technology is based around

concepts developed & proven for application in areas

where velocities and mass flow requirements are much

lower

• Synthetic and pulsing jets based on microfabrication and micro-

engineering concepts/active materials • Raises issues for practical implementation for robustness

A Question for Debate

As our focus moves to controlling flow

separation when the underlying flow energies

are increasing should we be looking to exploit

other flow actuation principles and concepts?

• Achieving a requisite blowing momentum by

increasing jet exit Mach number even more and

hence reducing mass flow requirements – better on

engine performance and pneumatic delivery system

• To achieve pulsing of high energy flows using

larger-scale, simpler, more reliable means

With Tangential LE blowing

Without Tangential LE blowing

High Mach Number – Lower Mass flow Actuation Systems

Supercritical tangential jet attachment

• Designed correctly (expansion and wall-

normal skewed velocity profile will work for

any exit Mach number

• Practical slot sizes

• Lower total massflow for given Cµ

• More compatible with engine bleed

pressures and pneumatic distribution

• Steady or pulsed A tangential wall jet designed

for NPR 5.0 operation

Alternative Flow Actuation Technology

• Rotating “siren” valve to generate a

pulsing jet

• Compact/ lightweight

• Robust and reliable • No reciprocating parts

• Efficient/low power consumption

• Can give high fqcy output (KHz)

• Potentially more easily to certify

• Fluidic Oscillators

• Being explored in AFLoNext

Summary

• Technologies for the active control of flow separation offer

commercial benefit and there is a rich programme of

development in the aerospace sector

• To be viable it is essential to focus as much on the

engineering implementation and certification of such

systems

• AFLoNext is taking a sensible approach and looks to be

delivering useful advances in the state of the art

Summary

However,

• We must be aware that as improved understanding

changes system requirements we should always keep an

open mind about adopting new engineering solutions and

embrace them rather than persevering with trying to adapt

solutions that were developed for a different set of

circumstances.

Thank you !

For more information:

Contact :

Clyde Warsop

BAE Systems Military Air and Information

clyde.warsop@baesystems.com

Or Contact@AFLonext.eu

September 2015 19