# THE GURNEY FLAP (PowerPoint)

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```					GURNEY FLAP
By:
KASYAP T V
S7 M2
27222
Introduction
 Principle behind gurney flap
 Experimental setup
 Results of experiment
 Hysterisis effect
 Applications
 Research areas
What is a Gurney Flap?

 A gurney flap is nothing
but a vertical tab attached
to the pressure side of
trailing edge of an
aerofoil.
 It is used as a high lift
device      intended     to
perform at low speeds.
 This has been proposed by
American aero dynamist
DAN GURNEY as a
spoiler in the rear of
racing cars.
Need for high lift devices
 The lift developed by an airfoil is directly
proportional to the velocity of flow.
 A high lift device can produce higher lift for
the same velocity.
 A high lift device reduces the stalling
speed(minimum speed) of aircrafts.
Principle of gurney flap
 Due to the sharp corner flap two counter rotating
vortices are formed.
 Total circulation around the aerofoil gets increased
Pressure distribution with
Gurney flap
Experimental Setup
 Rectangular plan form wing with
span=0.457m.
 Chord=0.154m
 Maximum thickness=10mm at 15% chord.
 Thickness chord ratio=0.065.
 Open jet low speed wind tunnel.
 Velocity range 4.1m/s to 15m/s.
Experimental Results
Effect on lift coefficient
 Increase in the lift is
proportional to the
flap height.
 Even after stall gurney
flap produces lift
greater than plain
aerofoil.
 maximum              lift
coefficient is increased
by 25%.
Effect on drag coefficient
 Coefficient   of drag
increases with the flap
height.
 Coefficient    of lift
increases faster then
drag coefficient till a
particular height of
flap.
Overall performance
 For Re=110,000 the
maximum
performance is
obtained at 5.5mm.
 Performance curve
shoes a negative trend
thereafter.
Height optimization
 From the overall performance curve the
optimum height is found to be 90% of the
boundary layer thickness.
 Hopt=0.9*t       where t=boundary layer
thickness
 Hopt=0.9*0.383x/(Re^0.2)
 Hopt=37.155*(c^0.8)*(u^-0.2)
Hysteresis Effect
 Causes the lift curve slopes to be different for
increasing and decreasing angle of attacks.
 It is caused by separation bubble effect.
What is a separation bubble?

to be separated in the laminar region itself.
 Flow reattaches in the turbulent region.
 Space between detachment and attachment
points is called a SEPARATION BUBBLE.
 If the flow is unable to reattach full
separation or stalling occurs
Short bubble hysterisis
 Occurs at the stall angle
 After the stall,in the while
decreasing the angle of
attack(downstroke)flow
reattaches at a lower angle
than the stall angle.
 A clockwise hysterisis
loop is formed in the lift
curve.
Long bubble hysterisis
 Occurs below the stall angle
 As angle of incidence is increased (upstroke) long
bubble grows larger.
 Just below the stall angle long bubble bursts to a
short bubble and lift drag ratio is improved.
 In the down stroke short bubble is transformed to
a long bubble only at lower angles
 hence improved glide ratio at during down stroke.
Glide ratio curves with
hysterisis

Clean aerofoil                 Gurney flap 5.5mm

Re = 65,000
Clean aerofoil                Gurney flap 5.5mm

Re=110,000
 Up to 40% increase in lift
 Improved glide ratio
 No moving parts
 Can easily be fitted
 Cheap
 Hysterisis effects are reduced to some
extend
 Cannot be used for high speed and
supersonic applications
 Gurney flap causes increased vibration on
wings.
Applications
 Rear spoilers for race cars
 Micro air vehicles
 Wind turbines
 Gliders
Research areas include……
 Application to helicopter rotors
 Application to delta wings
 Active gurney flaps for race cars
Conclusion
 The gurney flap is found to be a very useful
element in aerospace and automobile
industry which promises a bright future for
MAVs, race cars.
Bibliography
 The aeronautical journal(sept.2003)
 Aerodynamics
- L J Clancy
 The aerodynamic design of aircraft
- D Kuchemann F R S
 http://aerodyn.org/HighLift/gurney.html
 www.allamericanracers.com
 http://www.as.go.dlr.de/Transsonium4
 http://www.cfd.tu-berlin.de

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 views: 173 posted: 8/3/2011 language: English pages: 28
Kaja Hussain Engineer http://
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