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
September 2015 19