International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
REDUCTION OF VORTEX USING SLOTTER WINGLET
Karthikayan#1, Padmaseelan
#2
, Rahul Gouse#3
Guide: Mr N. Sivaselva Kumar
Department of Aeronautical Engineering
Park College of Technology, Coimbatore.
#1
[email protected]
#2
[email protected]
#3
[email protected]
ABSTRACT
This work represents the aerodynamic characteristic for aircraft wing with slotted winglet. This is
done by comparing the results of both bare and slotter winglet. It is one way of reducing vortex
caused by lift-induced drag. Slotter winglet being a small structure plays an important role in reducing
the vortex. By reducing vortex, induced drag and fuel consumption is reduced. This increases
operational range, endurance and also achievable speed. An experimental study is accompanied to test
the potentiality of Slotter winglet for the reduction of vortex strength and for the improvement of lift
coefficient without increasing the span of aircraft wing. The model composed of PSU 90-125
winglets. The test conducted in subsonic wind tunnel at various flow velocity and angle of attack from
-5 to +15 deg. The test result shows use of slotted winglet reduces drag coefficient by 20-25% and
increases lift coefficient by 10-20% than other winglets. Finally the percentage of wingtip vortices is
calculated by comparing to the results of bare winglet.
Keywords:
Slotter Winglet; Aerodynamics characteristic; Vortex; induced drag; wingtip vortices; wind tunnel
SYMBOLS
INTRODUCTION
α Angle of attack
It is well known that when a body exposed in a
viscous flow experiences profile drag, whether
it produces lift or not. The induced drag is a
different type of drag. It is caused by the
pressure imbalance at the tip of a finite wing
between its upper and lower surfaces. That
imbalance is necessary in order to produce a
positive lift force.
D Drag force
L Lift force
ρ Air density
Free stream velocity
Pressure coefficient
Drag coefficient
Lift coefficient
Moment coefficient
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However, near the tip the high pressure air from
the lower side tends to move upwards, where
the pressure is lower, causing the streamlines to
curl. This three dimensional motion leads to the
formation of a vortex, which alters the flow
field and induces a velocity component in the
downward direction at the wing. The induced
flow pattern causes the relative velocity to
downward direction of the wing, thus the lift
vector is tilted backward and a force component
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
in the direction of the drag appears, called
induced drag. Reducing the size of this tip
vortex and minimizing the induced drag is more
importance for the modern aircraft. For this
purpose the winglet concept is developed.
The main purpose of winglet is to improve the
aircrafts aerodynamic performance by
reducing the Induced drag. The vortices
produced at the wing –tips are unavoidable
products by the presence of lift and these
vortices are responsible for the appearance of
Induced Drag. In cruise conditions the induced
drag is responsible for approximately 30% on
entire drag and also 50% in high-lift
conditions.
Hence to reduce the induced drag, winglets
have been used and they also act as an
additional lifting surface on an aircraft. By
which fuel consumption goes down and range
is extended, this lead to achieve better lift.
There are several types of wingtip devices, and
although they function in different manners,
the intended effect is always to reduce the
aircraft's drag by partial recovery of the tip
vortex energy. Wingtip devices can also
improve aircraft handling characteristics and
enhance safety. Such devices increase the
effective aspect ratio of a wing without
materially increasing the wingspan.
The wing profile drag is the largest
contributor to the total aircraft drag at
cruise conditions for most aircraft. The
wing profile drag contributes about one
third of the total drag for transport aircraft.
The percentage of the total aircraft drag
due to the wing profile drag generally
increases, primarily because the relative
wing area. To minimize wing profile drag,
the figure of merit FOM applicable to
aircraft having their wing area determined
by a minimum-speed requirement (usually
landing speed) should be maximized:
s
FOM = ------------
Where
is the maximum lift
coefficient and
is the cruise
section profile drag coefficient. The figure
ISSN: 2349 - 9362
of merit is expressed in terms of Airfoil
characteristics, not aircraft characteristics.
The aircraft wetted area, can be reduced if
a higher maximum lift coefficient is
achieved, resulting in lower drag. The
wing profile drag can also be reduced if a
lower section profile-drag coefficient is
achieved. This figure of merit applies to
almost all classes of aircraft.
SLOTTER WINGLET
The new design approach "SLOTTER
WINGLET" is developed from the observation
of essential characteristic of winglet. Those
characteristic were proposed by the Richard T
Whitcomb who developed the concept of
winglet. A winglet should be effective for the
induced drag. Its effectiveness can be shown in
reduction of vortex. Initially a winglet should
consider three things in mean of reducing drag.
The first and foremost thing is strength of the
vortex. This strength is based on the vortex
flow and this strength is also in contact with
shape of the flow. The only way that vortex
can be reduced by affecting in its strength.
When there is an affect in its strength this will
be resulted in the induced drag. This induced
drag occupies a major role in the profile drag.
This profile drag is dominant in total drag in
an aircraft. This shows that when there is a
change in induced drag which is a drag due to
lift will result in change of total drag. The
shape, flow and strength are the three things
that to be considered while designing a winglet
All these three are in contact with each other,
so if there is a change in any one then that will
be resulted in other stuff. From this we can
have a clear note that the winglet should be
designed based on these characteristic. It
means that they should effective in reduction
of those parameters. The strength of vortex is
based on its continuity of the flow. If the
continuity is disturbed that will be hardly
reflected in strength of the vortex. From this
we come to know that the fore most thing to be
done to reduce the strength of the flow is to
create discontinuity in the flow. And the shape
of the vortex is also as important as flow of the
vortex. The flow of the vortex should be
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elliptical to reduce the strength of the flow. If
this is done the vortex will be reduced
effectively.
Slotter Winglet is a method for altering the
trailing tip vortex from an aircraft wing and
thus improves the aircraft performance. This
winglet is a device used to improve the
efficiency of aircraft by lowering the liftinduced drag caused by wingtip vortices. This
winglet provides an innovative method of
achieving the vortex arrangement described
above.
This slotter winglet is designed from the basic
model of winglet, the base model is nothing
but which is commercially being used in
aircraft. The Blended winglet is widely used in
aircraft because they are effective in reduction
of drag which is used nowadays and they are
economically friendly. Hence by doing an
optimization in the structure to achieve the
better efficiency a new type of winglet is
designed by introducing a slot in the winglet
called to be SLOTTER WINGLET.
The hand draft of designed slotter winglet is
shown below and the dimension’s mentioned
here all in feet. (Fig: 1)
Figure 1: side view of slotter winglet
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Figure 2: side and top view of wing
with slotter winglet.
An aircraft model’s wing with a set of
slotter winglet have been designed
and fabricated using plastic for testing
aerodynamic characteristic in subsonic
wind
tunnel
in
Aerodynamic
Laboratory. The NACA 0012 airfoil
has been used in root of the wing and
NACA 64008A airfoil has been used
in tip of the wing. PSU 90-125 WL
airfoil has been used in both root and
tip of the winglet. The winglet design
is shown in Figure 1. The aircraft
model has a span of 93.50ft.in.
The tests were carried out with freestream velocities of 28.36 m/s, and
40m/s respectively with bare winglet
and slotter winglet of different
configurations. The ambient pressure,
temperature and humidity were
recorded
using
barometer,
thermometer,
and
hygrometer
respectively for the evaluation of air
density in the laboratory environment.
The pitching moment, lift and drag
forces were measured by varying
angle of attack ranging from 0 degree
to 14 degree using the six-component
external balance. The coefficients of
lift, drag and moment are obtained
using the coefficient of lift equation:
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Coefficient of drag equation
Coefficient of moment equation
DESIGN
OF
WINGLET
WING
AND
An airfoil was designed to satisfy the set of
requirements using the Eppler Airfoil Design.
The result of this design effort is the NACA
0012 airfoil which is used at the root chord of
the wing because of its Pressure distribution is
along span wise at
and
Reduces the
total
combined with angle of inclination
( ) for the winglet. And NACA 64008A
airfoil is used at the tip of the wing due to its
Increases in the critical Mach number.
Allows low drag at high flight speed easier
takeoff is achieved. Considering winglet PSU
90-125 airfoil is used due to Operates at low
Reynolds number and Conservative design for
long range flight. Reduce span wise
aerodynamic loading. Induced drag is reduced
in wetted area. Avoid stall during climb due to
Narrow chord. The first two digits of winglet
in the design indicate the year the airfoil was
designed, 1990, and the last three are the
thickness ratio in per cent of chord, 12.5 per
cent. The desired lower lift coefficient limit of
the low-drag range was specified to be 0.5
which is higher than the actual design value
that is 0.2.
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At 4 degree angle of attack, the pressure
distribution has a nearly neutral gradient over
much of the lower surface. This distribution is
sufficient to maintain transition aft of the
50-percent chord location over most of the
operational Reynolds number range. As the
Reynolds number increases, the transition
location gradually moves forward due to the
boundary layer becoming less stable.
For angles of attack less than 4.0°, transition is
predicted to move quickly forward on the
lower surface. This rapid movement is
responsible for the sharp corner at the lower
limit of the low-drag range. The upper limit
of the low-drag range depends on the uppersurface pressure distribution at the lift
coefficient that corresponds to a = 4.0°.
At the low operational Reynolds numbers of
this airfoil, the proper management of laminar
separation bubbles is essential to a successful
design. This is accomplished on both surfaces
through the use of transition ramps that cause
transition to occur through shallow pressure
rises such that the separation bubble is
prevented. While transition ramps are typically
much less extensive, the long ramps employed
here are necessitated by the low Reynolds
numbers at which this airfoil operates.
WING AIRFOIL
Root chord- NACA 0012
Tip chord – NACA 64008A
WINGLET AIRFOIL
Root and tip chord- PSU 90-125
Specifications of the Wing
SL
NO
1
2
3
4
5
6
parameters
Sweep Angle
Span
Taper Ratio
Aspect Ratio
Area
Maximum root
chord
7
Minimum root
chord
8
Maximum tip
Chord
Tabulation 1: wing parameter
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Values
0
27
93.5
0.26
7.35
1135ft
18.5ft
1.5ft
5.13ft
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Specifications of the Winglet
SL
NO
1
2
3
4
5
6
parameter
Values
Span
Area
Sweep Angle
Taper Ratio
Maximum
Chord
Minimum
Chord
8.6ft
260
.26
1.5ft
1ft
Tabulation 2: winglet parameter
Results & Discussions
Without slot
Fig 12: Contours of absolute pressure (upper surface)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 13: Contours of turbulence intensity (upper surface)
Fig 14: Contours of turbulence intensity (lower surface)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 15: Contours of absolute pressure (wing airfoil)
fig 16: Contours of velocity magnitude (wing airfoil)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 16: Vector plot (wing airfoil)
Fig 17: Contours of absolute pressure (winglet airfoil)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 18: Contours of velocity magnitude (winglet airfoil)
Fig 18: Vector plot (winglet airfoil)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 19: Contours of absolute pressure (winglet
sFig 20: Path lines
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
WITH SLOT
Fig 3: Contours of absolute pressure (winglet airfoil)
Fig 4: Contours of velocity magnitude (winglet airfoil)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 5: Vector plot (winglet airfoil)
Fig 6: Contours of absolute pressure (winglet)
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 7: Contours of absolute pressure (winglet)
Fig 8: Contours of turbulent intensity
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 9: Contours of turbulent intensity
Fig 10: Path lines
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
Fig 11: Path lines
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
0.12
0.1
0.08
0.06
0.04
0.02
0
0
2
4
6
8
10
Fig 21: Angle of attack vs CD for bare winglet
1.37
1.36
1.35
1.34
1.33
1.32
1.31
1.3
1.29
0
2
4
6
8
10
Fig 22: Angle of attack vs CL for bare winglet
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
0.052
0.051
0.05
0.049
0.048
0.047
0.046
0.045
0.044
0
2
4
6
8
10
Fig 23: Angle of attack vs CD for slotter winglet
1.44
1.43
1.42
1.41
1.4
1.39
1.38
1.37
1.36
1.35
1.34
1.33
0
2
4
6
8
10
Fig 24: Angle of attack vs CL for slotter winglet
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International Conference on Explorations and Innovations in Engineering & Technology (ICEIET - 2016)
CONCLUSION
From the drag coefficient and lift coefficient graph it clearly shows that this slotted winglet will
increase lift force and reduce drag force. This winglet design is capable to reduce induced drag force
and also delays in wing stall.Slotted tips reduce drag because of the upwash at the wing tip. Winglet
increases the performance at low operational Reynolds number.
REFERENCE
[1] R. T. Whitcomb, Methods for Reducing Aerodynamic Drag, NASA Conference Publication 2211,
Proceedings of Dryden Symposium, Edwards, California, 1981.
[2] R.T.Whitcomb, A Design Approach and Selected Wind-Tunnel Results at High Subsonic Speeds
for Wing-Tip Mounted Winglets, 1976
[3] Chandrasekharan, M. Reuben, Murphy, R. William, Taverna, P. Frank, and B. W. Charles,
Computational Aerodynamic Design of the Gulfstream IV Wing, AIAA-85-0427, 1985..
[4] J. J. Spillman, The use of wing tip sails to reduce vortex drag, Aeronautical Journal, September,
pp.387-395,1978.
[5] Maughmer, M. D., The Design of Winglets for High-Performance Sailplanes", AIAA Paper 20012406-CP, 2001.
[6] Nazarinia, M., Soltani, M. R., Ghorbanian, K., Experimental Study of Vortex Shapes behind a
Wing Equipped with Different Winglets", Journal of Aerospace Science and Technology, Vol. 3,
[7] Spalart, P. R., Allmaras, S. R., A One-Equation Turbulence Model for Aerodynamic Flows",
AIAA Paper 92-0439-CP, 1992. Spillman, J., The use of Wing Tip Sails to Reduce Vortex Drag",
Aeronaut. J., 82, 1978, pp. 387-395.
[8] J. E.Yates, and C. Donaldson, Fundamental Study of drag and an Assessment of Conventional
Drag-Due-To-Lift Reduction Devices, NASA Contract Rep 4004, 1986.
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