1. GURNEY FLAP
By:
KASYAP T V
S7 M2
27222

2. Introduction Principle behind gurney flap Experimental setup
Results of experiment
Hysterisis effect
Advantages & Disadvantages
Applications
Research areas

3. 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.

4. 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.

5. 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.

7. Pressure distribution with Gurney flap

8. 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.

9. Experimental Results

10. 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%.

11. 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.

12. Overall performance
For Re=110,000 the maximum performance is obtained at 5.5mm.
Performance curve shoes a negative trend thereafter.

13. 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)

14. Hysteresis Effect
Causes the lift curve slopes to be different for increasing and decreasing angle of attacks.
It is caused by separation bubble effect.

15. 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.

16. Space between detachment and attachment points is called a SEPARATION BUBBLE.
If the flow is unable to reattach full separation or stalling occurs

17. 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.

18. 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.

20. Features of hysteresis effects
Strongly depends on the geometry of aerofoil
Reynolds number has pronounced effect on them
Generally unfavorable to aircrafts

21. Glide ratio curves with hysterisis
Clean aerofoil
Gurney flap 5.5mm
Re = 65,000

22. Gurney flap 5.5mm
Clean aerofoil
Re=110,000

23. 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

24. Disadvantages
Cannot be used for high speed and supersonic applications
Gurney flap causes increased vibration on wings.

25. Applications Rear spoilers for race cars Micro air vehicles
Wind turbines
Gliders

26. Research areas include……
Application to helicopter rotors
Application to delta wings
Active gurney flaps for race cars

27. 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.

28. Bibliography The aeronautical journal(sept.2003) Aerodynamics
- L J Clancy
The aerodynamic design of aircraft
- D Kuchemann F R S

29. THANK YOU