7/28/2019 Seminar Em 1

1/29

7/28/2019 Seminar Em 1

2/29

Introduction

Principle behind gurney flap

Experimental setup

Results of experiment

Hysterisis effect

Advantages & Disadvantages

Applications

Research areas

7/28/2019 Seminar Em 1

3/29

TERMINOLOGY

AEROFOILGenerally wing section of the aeroplane which

produces aerodynamic forces when air or any fluid

flows around it

AILERONS

Ailerons are control surfaces at the outer part of the

wing which operate differently to raise the lift on one

side of the wing and to lower the other

FLAPS

Movable surface on the leading edge of the wing to

permit higher lift during take off.

7/28/2019 Seminar Em 1

4/29

AERODYNAMICS OF AN AERO FOIL

Lift

Drag

7/28/2019 Seminar Em 1

5/29

What is a Gurney Flap?

A gurney flap is nothingbut a vertical tab attachedto the pressure side of

trailing edge of anaerofoil.

It is used as a high liftdevice intended to

perform at low speeds.

This has been proposed byAmerican aero dynamistDAN GURNEY as aspoiler in the rear ofracing cars.

7/28/2019 Seminar Em 1

6/29

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 forthe same velocity.

A high lift device reduces the stalling

speed(minimum speed) of aircrafts.

7/28/2019 Seminar Em 1

7/29

Principle of gurney flap

Due to the sharp corner flap two counter rotating

vortices are formed.

Total circulation around the aerofoil gets increasedwhich adds to the lift.

7/28/2019 Seminar Em 1

8/29

7/28/2019 Seminar Em 1

9/29

Pressure distribution with

Gurney flap

7/28/2019 Seminar Em 1

10/29

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.

7/28/2019 Seminar Em 1

11/29

Experimental Results

7/28/2019 Seminar Em 1

12/29

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%.

7/28/2019 Seminar Em 1

13/29

Effect on drag coefficient

Coefficient of drag

increases with the flap

height.

Coefficient of lift

increases faster then

drag coefficient till a

particular height offlap.

7/28/2019 Seminar Em 1

14/29

Overall performance

For Re=110,000 the

maximum

performance is

obtained at 5.5mm.

Performance curve

shows a negative trend

thereafter.

7/28/2019 Seminar Em 1

15/29

Hysteresis Effect

Causes the lift curve slopes to be different for

increasing and decreasing angle of attacks.

It is caused by separation bubble effect.

7/28/2019 Seminar Em 1

16/29

What is a separation bubble?

Strong adverse pressure gradient causes the flowto be separated in the laminar region itself.

Flowreattaches in the turbulent region.

7/28/2019 Seminar Em 1

17/29

Space between detachment and attachment

points is called a SEPARATION BUBBLE.

If the flow is unable to reattach fullseparation or stalling occurs

7/28/2019 Seminar Em 1

18/29

Short bubble hysterisis

Occurs at the stall angle

After the stall,in the while

decreasing the angle of

attack(downstroke)flowreattaches at a lower angle

than the stall angle.

A clockwise hysterisis

loop is formed in the liftcurve.

7/28/2019 Seminar Em 1

19/29

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.

7/28/2019 Seminar Em 1

20/29

7/28/2019 Seminar Em 1

21/29

Glide ratio curves with

hysterisis

Clean aerofoil Gurney flap 5.5mm

Re = 65,000

7/28/2019 Seminar Em 1

22/29

Clean aerofoil Gurney flap 5.5mm

Re=110,000

7/28/2019 Seminar Em 1

23/29

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

7/28/2019 Seminar Em 1

24/29

Disadvantages

Cannot be used for high speed and

supersonic applications

Gurney flap causes increased vibration onwings.

7/28/2019 Seminar Em 1

25/29

Applications

Rear spoilers for race cars

Micro air vehicles

Wind turbines

Gliders

7/28/2019 Seminar Em 1

26/29

Research areas include

Application to helicopter rotors

Application to delta wings

Active gurney flaps for race cars

7/28/2019 Seminar Em 1

27/29

Conclusion

The gurney flap is found to be a very useful

element in aerospace and automobile

industry which promises a bright future forMAVs, race cars.

7/28/2019 Seminar Em 1

28/29

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

http://aerodyn.org/HighLift/gurney.htmlhttp://www.allamericanracers.com/http://www.as.go.dlr.de/Transsonium4http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.cfd.tu-berlin.de/http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.as.go.dlr.de/Transsonium4http://www.allamericanracers.com/http://www.allamericanracers.com/http://aerodyn.org/HighLift/gurney.htmlhttp://aerodyn.org/HighLift/gurney.html

7/28/2019 Seminar Em 1

29/29