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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
 Advantages & Disadvantages
 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
  which adds to the lift.
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?




 Strong adverse pressure gradient causes the flow
  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
       Advantages of gurney flaps
 Up to 40% increase in lift
 Improved glide ratio
 No moving parts
 Can easily be fitted
 Cheap
 Hysterisis effects are reduced to some
  extend
       Disadvantages
 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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posted:8/3/2011
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Kaja Hussain Kaja Hussain Engineer http://
About I am a Mechanical Engineering graduate. I am so fond of Cars & Bikes. I also love web designing and Blogging :)