Flow Anlaysis on Hal Tejas Aircraft using Computational Fluid Dynamics with Different Angle of Attack

International Journal of Advanced Engineering, Management and Science (IJAEMS) [Vol-3, Issue-5, May- 2017]
https://dx.doi.org/10.24001/ijaems.3.5.31 ISSN: 2454-1311
www.ijaems.com Page | 591
Flow Anlaysis on Hal Tejas Aircraft using
Computational Fluid Dynamics with Different
Angle of Attack
Abhishek Jain1
, S. K. Sharma2
, Comandur Rajasekhar Kaushik3
, Abhishek Gour4
1,2
Assistant Professor
1,2,3,4
Mechanical and Automation Engineering, Amity University Rajasthan, Jaipur, India
Abstract— In the current globalization, we can see many
innovations being introduced or implemented in every
aspect of field that are considered to be existed. Every
country is aiming to develop its power over all the aspects
that considered for comparison with other countries in
order to stand at same level of competition with others.
One such power considered by all countries to develop
every possible way to have a healthy competition is the
military power which involves basically innovations of fast
moving aircraft having a high lift coefficient and low drag
coefficient. Such an aircraft having the high lift and low
drag coefficient is TEJAS (HAL) developed by country India
on which the purpose of paper mainly sustains. The paper
mainly focuses on steady-state flow analysis over aircraft
TEJAS using the computer aided modelling techniques and
also the comparison of the results obtained from the
modelled techniques. The paper also outlines the designing
of the structural model of the TEJAS in a modelling
software, creation of a finite computational domain,
segmentation of this domain into discrete intervals,
applying boundary conditions such as velocity in order to
obtain plots and desired results determining the coefficient
of pressure, lift and drag coefficient, velocity magnitude etc.
This paper also aims in creating awareness to the future
students about the techniques involved and knowledge
required for developing a designed modelled. This paper
also highlights the use of CFD techniques involved for the
purpose of fluid flow simulation of the aircraft especially
performing the meshing techniques, pre and post processing
techniques and finally the evaluation of the simulation.
Finally this paper can be seen as source by future
generation students in gaining knowledge about design,
analysis and simulation of the structured model on various
conditions, about the field of aerospace engineering and
new innovations being developed and also about the career
involved when the above fields were chosen foe
specialization purposes
Keywords— Ansys Fluent, Catia Software.
I. INTRODUCTION
An aircraft is a well designed structured body basically
used for moving in air by gaining the strength from
atmosphere as it moves against the force of gravity. In
earlier days aircraft were seen as transportation medium but
with the increase in new ideas and innovations, aircraft
were introduced into the military power, thus we could see
aircraft flying during the world wars. As development in the
globalization continued, the development in many fields
also enhanced. With these developments we can see many
new innovations in designs of aircraft to make it as
innovative as possible. One such innovation were, the
considerations of properties such as the static and dynamic
lift to counter the gravitational force in order to fly the
aircraft at great heights and also to withstand against the
force of thrust. Thus the present generation aircrafts include
a lot of multidisciplinary designs to achieve critical mission
requirements such as endurances, manoeuvrability, fuel
consumption, payload capacity, noise emission etc when
compared to the older ones. But these critical requirements
can only be achieved with the help of aerodynamic property
of an aircraft such as the drag, vortex, etc. The aerodynamic
force is found to be a central idea behind the design of an
aircraft. An important aspect of this aerodynamic force is
the induced drag that approximates about 33% of the total
aerodynamic force when caused by the lift and during the
low speed movement achieved at the time of landing and
takeoff situation, it accounts for 80%-90% of the total drag.
The streamline present on an aircraft is also important
aspect of design in determining difference in pressure
between upper and lower surface of the aircraft body. The
finite wings present in an aircraft also plays major role in

designing since at the tip of the wing, there is leakage of air
molecules. So these finite wings are provided with the wing
tip sails in order to produce the required thrust during the
generation of lift. However research are still performed in
order to bring new innovations in these designs of aircraft
body and also to increase its efficiency. Apart from these
characteristics some of the other important aspects
considered for an aircraft design are the environmental
factors such as types of pollution, sudden climatic changes
due to increase in global warming and many other factors
that play a vital role for future growth. Nowadays travelling
in air depends mostly on the environment thus making the
power factor in the aircraft design. The figure below shows
the structured model of an aircraft.
Fig.1: Modeling of F-16 HAL TEJAS Aircraft using Solid works 2015
The structured model shown above is designed from the
specifications of the model TEJAS introduced by Hindustan
Aeronautical Limited, India. The aircraft TEJAS is well
developed product which came into light from the Light
Combat Aircraft (LCA) programme in the year 1980. It was
considered as replacement to the single fighter flights since
TEJAS is a multi-role fighter. The design of TEJAS
consists of many disciplinarians out of which some
properties such as the highly supersonic, highly
manoeuvrable and also the lightest body are considered
important. It is made of composite material structures and
the aerodynamic design, is a combination of an intense
design process involving wind tunnel studies and utilization
of extensive Computational Fluid Dynamics, the subject
which basically used for the simulation of structured models
for the analysis of the fluid flow. It has Specific
aerodynamic features that provide excellent aircraft
performance in a wider flight envelope. The dimensions of
TEJAS considered during the design of structured model
are, Wing span which is about 8.20m, while length and
height measures about 13.20m and 4.40m. The weight of
the aircraft while takeoff clean is 9800kg, during empty is
6560kg and about external stores is 3500kg. Its max speed
is supersonic at all altitudes. Its service ceiling is 50,000ft
and ‘g’ limits are +8/-3.5.(12)
. Apart from the consideration
of these specifications for the design of the structured
model, the study about the area Computational Fluid
Dynamics (CFD) was also done for the further proceeding
of the paper.CFD is a branch of study of fluid mechanics
involving algorithms and numerical methods to solve and
analyse the problems of fluid flows. Nowadays CFD is
basically studied for performing advanced calculation
purposes that are achieved by running the software. With
the introduction this software, any complex scenarios
involving turbulent flows or transonic flows can be
calculated with accuracy and speed. Many of the flight tests
involving validation of the properties considered during the
design and simulation analysis of the structural body of
design on the basis of fluid flow can be achieved easily with
this CFD based software. The calculation of Navier–Stokes
equations is easily achieved through this software that is
basically used for calculating the single phase fluid flows.
Apart from these terms another term considered in this
paper is the “Angle of Attack”, on which the whole results
of the paper are been drawn. It is basically defined as the
angle between a reference line on a body (often the chord
line of an airfoil) and the vector representing the relative
motion between the body and the fluid through which it is
moving. The below figure the structured design of the
model TEJAS be shown in terms of measurement of “Angle
of Attack”.

II. ANGLE OF ATTACK
Fig.2: Showing the basic measure of Angle of Attack
III. METHODOLOGY AND BOUNDARY
CONDITIONS
A. Creation of geometry:
The structural model of TEJAS is designed using the
SOLID WORKS 2015 software for the purpose of
simulation and analysis.(11)
B. Mesh generation:
The designed model was imported into ANSYS Work
Bench and meshed appropriately. The meshing tools like
mapping and inflation cannot be employed while meshing
as it is symmetrical in shape and gives a very fine mesh.
Once the process of meshing is completed , it is then
exported to ANSYS Fluent 14, where the simulation of
fluid flow analysis is performed.(11)
C. Simulation of the Continuum:
Here the simulation of structured body is performed in
ANSYS Fluent 14. In this the meshing of the body is
checked and once the software approves it, the models,
materials and boundary conditions are set. (11)
1. Model:
The model used for this kind of simulation is the K-E
model.(11)
2. Materials:
The air is considered as a working fluid for the
purpose of simulation in this paper and is allowed to
act on the aircraft at an altitude of 50,000 ft. Only
density is considered as the material property of the air
and is constant i.e. 1.225 kg/m3. (11)
3. Boundary Conditions:
The important boundary conditions considered for the
purpose of the external flow analysis are the Mach
number which is considered as inner boundary
condition, is taken as Mach2 i.e. the velocity of inlet
taken as 553m/s and speed of sound at this altitude is
334.72 m/s. The outer boundary condition is taken as
pressure and its value taken as 0 Pascal. The rest of the
faces of continuum are considered symmetry which
means that the faces are under no-slip condition i.e.
flow condition does not apply on these faces.(11
4. Solution:
Once the boundary conditions are set, the solution
methods and controls are set for this simulation. The
solution method set for this is the coupled solver. And
as for the solution controls the courant number is set to
0.25 and the under relaxation factors for momentum
and pressure are set as 0.75 and for the turbulent
kinetic energy, turbulent dissipation rate and turbulent
viscosity is set to 0.8. (11)
5. Analysis:
The CFD Analysis and study of results are carried out
in 3 steps: (1) Pre-processing, (2) Solving and (3)
Post-processing by using fluent solver in ANSYS
work bench.(11)
Velocity Inlet: The inlet boundary conditions involve
velocity components for varying angle of attack, turbulence
intensity and turbulent viscosity ratio. (11)
Pressure Outlet: Ambient atmospheric condition is
imposed at outlet. The velocity components are calculated
for each angle attack case as follows. The x-component of

velocity is calculated by x =ucos(x) and the y component
of velocity is calculated by y =usin(x), where (x) is the
angle of attack in degrees.(11)
Symmetry: This is the boundary wall to see the analysis. (11)
Operating condition: The inlet velocity taken for fuselage
533 m/sec, for different angle of attack of air at normal
degree, 4 degree and 8degreee and at STP
(Temperature=300k, Pressure=101325pa) as the fluid
medium.(11)
6. Properties of Air: (11)
Density: ρ = 1.225 kg/m3
Viscosity: μ= 1.7894e-05 kg/m-s
Solvers selection: Pressure based solvers.
Mathematical models: K- ε standard wall function
Solution controls: Gauss-Seidel flow turbulence energy.
Momentum: Second Order Upwind Scheme
Initialization: Inlet Values
Force Monitors: Lift and Drag
Reference values: Inlet Values
Convergence Limit: 1x10-9
IV. RESULTS AND DISCUSSION
The analysis to be performed on all cases is carried out in ANSYS FLUENT software. Results of the analysis are drawn and are
shown below using Analysis Post processor. Velocity, pressure and residual plots are plotted on all cases of study.
Test case I:
Fig.3.1: Velocity contour at a normal degree angle .
Fig.3.2: Pressure contour at normal degree angle.

RESIDUAL PLOT:
Graph I: It shows the iterations of residual results.
Test case II:
Fig.4.1: Velocity contour at 4 degree angle.
Fig.4.2: Pressure contour at 4 degree angle

RESIDUAL PLOT:
Graph II : It shows iterations of residual results.
Test case III:
Fig.5.1: Velocity contour at 8 degree angle.
Fig.5.2: Pressure contour at 8 degree angle

RESIDUAL PLOT:
Graph III : It shows iterations of residual results.
The above figures and graphs show the results being drawn
in case of pressure distribution, velocity of air and density
of the aircraft. During the movement of the aircraft in the
stream of air, the velocity flows along the upper and lower
surface of the aircraft and also along the leading edge of the
aircraft. Further at downstream, the velocity moves along
the tailing edge and this velocity is considered to be high
i.e. approximately 85% of the free stream velocity.
According to Bernoulli’s equation, as velocity increases the
pressure decreases and vice versa. Thus a higher pressure is
observed at lower surface of the body which is more than
the ambient pressure at the upper surface of the aircraft
body that is considered to be low. Further by increasing the
“angle of attack”, the velocity distribution also changes
which can be seen in the above figures, shown at ‘angle of
attack’ of 0 degrees, 4 degrees, 8 degrees respectively.
From the above figures, it is observed that there is an
increase in velocity at the upper surface while a decrease at
the lower surface. Also an increase in pressure difference
will result in an increase in the lift and is found to be same
in case of density also. We can observe from the figures that
for each “angle of attack”, the flow of velocity and the
distribution of pressure vary. The value velocity at the top
and bottom surface of aircraft at normal degree of “angle of
attack” is relatively small. Hence the value of pressure
distribution at this point is also small resulting in a small
lifting force. At this point the flow over the wing still
remains dominant. On the other hand there is large amount
of energy loses during the separation of boundary layer
and this energy loss in most applications adversely affects
the aerodynamic lift and increase in drag. So an increase in
“angle of attack” increases the drag while the reduction in
the drag results in energy and fuel consumption. The above
figures show mostly the positive pressures than the negative
pressures. So an increase in “angle of attack” results an
increase in coefficient of lift, affecting the aerodynamic
characteristics of the body. At this state, the flow separation
tends to act at the bottom edge of the body since the
pressure at the bottom edge is less than the pressure at the
top edge. The resultant pressure is the sum of the top
surface positive pressure and bottom surface negative
pressure. However sometimes due to changes in the design
conditions, the bottom surface is carrying the positive
pressure while the top surface is carrying the negative
pressure. The positive pressure at the bottom edge
determines the shape and thickness of the airfoil. Large
positive values at the bottom edge imply more severe
adverse pressure gradients. Thus due the increase in “angle
of attack”, the pressure increases from the minimum at the
top edge to the value at the bottom edge which is considered
to be maximum at that point. This total region is considered
as the pressure recovery region and this pressure is
associated with the boundary layer transitions. Thus finally
the flow separation occurs when the pressure is too high at
higher “angle of attack”.
V. GRAPHS AND TABLE
After performing required simulation, the values of
Velocity, pressure and density with a different “angle of
attack” were observed. After observing the results, the
following graphs at each degree are drawn in order show
the increase and decrease in the respective values giving an
idea about the performance of the aircraft to analyse

Graph showing the results of the test I:
Graph 1.1: Density graph of the aircraft at normal angle
Graph 1.2: Pressure graph at normal angle
Graph 1.3: Velocity magnitude graph at normal degree

Graphs showing the results of test II:
Graph 2.1: Velocity magnitude graph of the aircraft at 4 degree angle
Graph2.2: Pressure graph at 4 degree angle
Graph2.3: Density graph at 4 degree angle

Graph showing the results of test III:
Graph 3.1: Velocity magnitude graph at 8 degree angle
Graph3.2: Pressure graph at 8 degree angle
Graph 3.3: Density graph at 8 degree angle

VI. CONCLUSSION
This study shows the following conclusion:
After the analysis of the simulated flow over the aircraft on
different properties considered, the following conclusions
were drawn
 As “angle of attack”’ increases, the velocity increases
and centre of pressure difference moves forward. If the
angle of attack decreases the pressure difference
moves rearward i.e. towards the bottom edge. .
 For a normal degree of “angle of attack” with a speed
of 533 m/s, it is observed that the maximum velocity
is 2.405e+004m/s and total pressure acting is
1.003e+008pa.
 At 4degree of “angle of attack” with speed of 533
m/s, it is observed that maximum velocity is
3.592e+005m/s, and total pressure is about
1.942e+011pa.
 At 8degree of “angle of attack’ with speed of 533 m/s,
it is observed that maximum velocity is
3.772e+005m/s and total pressure is about
9.406e+009pa.
 Finally from the values of the result it can concluded
that the drag and lift coefficient of the aircraft depends
on the airfoil shape and also on the velocity
distribution.
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[15] https://en.wikipedia.org/wiki/Angle_of_attack

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