International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 1- May 2016
Numerical Analysis of Drag Reduction
Method Using Vortex Generator on
Symmetric Aerofoil
1
P Jennifer Vinodhini, 2T Jebin Samuvel, 3 G Samuel Raj
1
Student,2 Assistant Professor3Student
Sri Shakthi Institute of engineering and technology
Chinniyampalayam, Coimbatore,
Tamil Nadu-641062, India
Abstract—Design and analysis of vortex generator
by using Computational Fluid Dynamic on Subsonic
Aircraft model is carried out on this project. One of
the main causes of aerodynamic drag is the
separation of flow near the aircraft’s rear end. To
control the flow separation, various shapes of vortex
generator is tested for application on the roof of
aircraft wing surface. A vortex generator is an
aerodynamic device, consisting of a small vane that
creates a vortex. It modifies the flow around the
surfaces affecting boundary layer and controlling
the flow separation. The objective of the project is
introducing the delta wing shape vortex generator
and determining the percentage of drag reduction,
which is designed by Computer Aided Design in
CATIA V5 software. Vortex generator reduce drag
by preventing flow separation at downstream of the
aircraft wing. Drag Force values can be obtained by
using output of CFX Besides that, CFX simulation
results of streamline flow at the rear end of
symmetric Airfoil model is also obtained.
Comparison of drag coefficient values of the model
with Various Shapes of vortex generator must be
done and the most efficient shape is important to
achieve is the project objectives.
Keywords—External flow, Boundary layer theory,
Flow separation and Drag coefficient.
INTRODUCTION
A vortex generator is an aerodynamic device,
consisting of a small vane usually attached to a
lifting surface (such as an aircraft wing) or a rotor
blade of a wind turbine. When the airfoil or the body
is in motion relative to the air, the vortex generators
creates a vortex, which, by removing some part of
the slow-moving boundary layer in contact with the
airfoil surface, delays local flow separation and
aerodynamic stalling, thereby improving the
effectiveness of wings and control surfaces, such
as flaps, elevators, ailerons, and rudders. The effect
of flow with and without vortex generator is shown
below.
ISSN: 2231-5381
Fig. 1 Function of vortex Generator
A very effective yet simple solution to avoid
separation is to use tabulators/Vortex generators.
Each of these small elements creates a swirling wake
that places an energy in the boundary layer of the
wing. The result is a higher critical angle of attack, a
lower
stall
speed,
and
gentle
stall
characteristics. The
vortex
generators
affect
boundary layer in the flow around the
airfoil. Turbulent boundary layer is more resistant to
separation. In this way it is possible to fly at a slower
speed and higher angles of attack. Vortex Generators
on stabilizers act similarly improving the
effectiveness of control at low speeds and with high
deflections of control surfaces. Proper location of
vortex generators is very important. They should be
positioned precisely in the transition region of the
boundary layer.
Situation is somewhat complicated by the fact
that transition region, depending on the flow
conditions and angle of attack, changes its position.
If Vortex generators will be too close to the leading
edge - will be in the laminar boundary layer and
cause excessive drag during cruise, but if they are
too far from the leading edge -their effectiveness at
high angles of attack and low flight speed may be
affected. The optimal mounting location can be
determined by computer simulations, wind tunnel
testing or during test flights.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 1- May 2016
SELECTION OF AIRFOIL
The primary function of the wing is to generate
lift force. This will be generated by a special wing
cross
section
called
airfoil.The NACAaerofoils are aerofoil shapes
for
aircraft wings developed by the National Advisory
Committee for Aeronautics (NACA). The shape of
the NACA aerofoils is described using a series of
digits following the word “NACA”.
Example: The NACA 0012 airfoil is symmetrical,
the 00 indicating that it has no camber. The 12
indicates that the airfoil has a 12% thickness to
chord length ratio, it is 12% as thick as it is long.
Fig. 2 NACA 0012 airfoil
DESIGN CONSIDERATIONS
A. Determining
Generators
the
Shape
of
the
Vortex
should be placed just in front of the laminar to
turbulent transition of the boundary layer on your
wing. This transition point is located at
approximately 16% back on the wing chord from the
leading edge. The Vortex Generators are placed just
in front of the laminar to turbulent boundary layer
transition.
C. Determining The Working Angle
The airfoil is placed at the angle of the 0°.The
drag force is foundwith various Vortex Generators
on itwhere flow separation creates a large dead air
region of slow moving eddying flow where the
stream lines are broken up and a reverse flow is
observed and the local direction of flow is opposite
to that of the outer flow. The effect of reverse flow
was taken into considerations.
D. Determining The Height Of The Vortex
Generators
Vortex Generators work to control the boundary
layer and thus they are most effective inside the
boundary layer. On larger general aviation aircraft
and airliners, Vortex Generators typically have a
height 80% that of the laminar boundary layer right
before the laminar to turbulent transition point on the
wing. However, on model aircraft that will typically
result in a Vortex Generator with a height well less
than 1/64th of an inch (my model has a boundary
layer height of 0.00097 inches). This makes them
very hard to manufacture and thus we have made the
Vortex Generators have a height of 1/8th of an inch
to make them easier to handle.
There are many types of Vortex Generators being
used on aircrafts today as shown in Fig. 3. Out of
these shapes gothic and rectangular vortex
generators are considered for comparison.
E. Calculate Span Wise Spacing Of Vortex
Generators
Fig. 3 Various Shapes of Vortex Generators.
COMPARISON OF DRAG FOR VARIOUS VORTEX
GENERATOR SHAPES AT 0° ANGLE OF ATTACK.
The vortex generator shapes of rectangular and
gothic are taken for consideration. The cad model of
the rectangular vortex and gothic vortex generator
with symmetric airfoil is shown below.
B. Determining The Length Of Vortex Generator
And Their Location Along The Chord Of The
Wing
After determining the radius of the vortices being
produced by the Vortex Generators, it is recommend
to space the Vortex Generators at least two radius
away from each other and also that Vortex
Generators be placed at a 15° to the flow over the
wing. This will allow the Vortex Generator to work
effectively and produce the largest vortices. The
Vortex Generators can be placed on the 1/3rd to ½
span of the wing. This makes the inboard sections of
the wing will stall first while the outboard section
continues to have smooth airflow.
Next we determined the length of the Vortex
Generators and where along the chord of the wing
the Vortex Generators will be placed. The length of
the Vortex Generator should be around 5-8% of the
chord length of the wing. The Vortex Generator
ISSN: 2231-5381
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 1- May 2016
Domain - Default Domain
Type
Fluid
Location
B754
Materials
Air Ideal Gas
Fig 3 Rectangular Vortex generator on symmetric
airfoil
Fluid Definition
Material Library
Morphology
Continuous Fluid
Settings
Buoyancy Model
Non Buoyant
Domain Motion
Stationary
Reference Pressure
1.0000e+00 [atm]
Heat Transfer Model
Isothermal
Fluid Temperature
Fig 4 Gothic Vortex generator on symmetric
airfoil
The delta wing shape vortex generator is a new
shape that is inspired by the shark fin antenna on
BMW car. The cad image of the delta wing vortex
generator is shown below.
2.5000e+01 [C]
Turbulence Model
k epsilon
Turbulent Wall Functions
Scalable
Table 1 Domain Physics for CFX
Domain
Boundaries
Boundary – inlet
Type
INLET
Location
F760.754
Settings
Flow Regime
Subsonic
Mass And
Momentum
Normal Speed
Fig 5 delta wing Vortex generator on symmetric
airfoil
MESHING
For acquiring accurate CFD results, superior
meshing technology is required.ANSYSMeshing
provides a multitude of meshing technologies in a
single application to allow users to select the best
option on a part by part basis. This ANSYS CFX
results include unlimited mesh editing capabilities as
well as structure hexahedral meshing. In order to
know whether the data entered was feasible or not, a
simple coarse meshing was initially done. Once the
solution was found to converge, we moved on to fine
meshing.
Normal Speed
2.5000e+02 [m s^-1]
Medium Intensity and Eddy
Viscosity Ratio
Turbulence
Boundary – outlet
Default
Domain
Type
OUTLET
Location
F756.754
Settings
Flow Regime
Mass And
Momentum
Subsonic
Average Static Pressure
Pressure Profile
Blend
5.0000e-02
Relative
Pressure
0.0000e+00 [Pa]
Pressure
Averaging
Average Over Whole Outlet
Boundary - Default Domain Default
Settings
The set up for meshing is shown below.
ISSN: 2231-5381
Mass And
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No Slip Wall
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International Journal of Engineering Trends and Technology (IJETT) – Volume 35 Number 1- May 2016
Momentum
Wall Roughness
Smooth Wall
Table 2 Boundary conditions
ANSYS SOLUTION
The ANSYS 14.0 is used here to get the drag
force values. The drag force for various shapes
of vortex generators on symmetric airfoil is
shown below. The image indicates the velocity
distribution and the drag values being indicated
at the left side.
A. Drag Value
Generator
For
Rectangular
Fig.8 Drag Force for delta wing Vortex generator
at 0° (D= 16783.7 N)
RESULT
Vortex
S.NO
Vortex Generator Shapes
Drag
Drag
Force at
Coefficient at
0 (N)
0
2
Rectangular Shapes
21288.9
0.008797
3
Gothic Shapes
16916.1
0.006990
4
Delta Wing Shapes
16783.7
0.006936
The drag force values are taken from the ANSYS
results and the drag coefficient values are derived from
theoretical formula. The formula is shown below:
D = 1/2 v2SCd
CONCLUSION
Fig.6 Drag Force for Rectangular Vortex
generator at 0° (D= 21288.9 N)
B. Drag Value For Gothic Vortex Generator
The drag force values for all shapes of vortex
generators were found and the results were
compared.
According to our analysis, the Delta wing Shape
vortex generator gives minimum amount of drag
force and also delays flow separation through
increasing velocity near the surface.
REFERENCE
1)
2)
3)
Fig.7 Drag Force for gothic Vortex generator at 0°
(D= 16916.1 N)
4)
5)
C. Drag Value For Delta wing Vortex Generator
6)
7)
8)
ISSN: 2231-5381
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The coordinate points of „NACA 0012‟ was taken from
„UIUC Airfoil datasite‟.
D.Anderson, J. R.(1984). „Fundamental of Aerodynamics‟.
David Joseph Ronald Tucker. (2013), „An Experimental
Study of Hemispherical Vortex Generators for Separation
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