ABSTRACT
Numerical
Simulation of incompressible flow has been performed on the ABU CAR 11
model moving at a speed of 40m/s. Solid Works was used to create the 3D
CAD model of the car. ANSYS Fluent, the computational fluid dynamics
software was used to perform the computation. All the analysis have been
carried out computationally in the CFD software
―ANSYS
Fluent 15‖ and the CAD modeling in ―Solid Works 2014‖.The analysis was
performed to study the flow behavior of air over the car body. The final
values of the coefficients of drag, lift and momentum were found to be
3.41e-01, 3.55e-01,-5.47e-01 respectively. The analysis also included
the studies of contours of pressure and velocity that impact the car
body and it was found the drag could be reduced by streamlining the car
body, creating perforations in the front of the car and introducing a
diffuser.
Table of Contents
Declaration.......................................................................................................................................... 2
Dedication........................................................................................................................................... 3
Certification........................................................................................................................................ 4
Acknowledgement.............................................................................................................................. 5
Abstract............................................................................................................................................... 6
List
Of
Figures.................................................................................................................................... 9
Nomenclature.................................................................................................................................... 10
1 Chapter One.............................................................................................................. 11
1.0
Introduction........................................................................................................................... 11
1.1
Background Of
Study............................................................................................................ 11
1.2
Problem
Statement................................................................................................................. 13
1.3
Present
Work.......................................................................................................................... 13
1.4
Aim And
Objective................................................................................................................ 13
1.5
Justification............................................................................................................................ 14
1.6
Scope...................................................................................................................................... 14
2 Chapter Two................................................................................................................................. 16
2.0
Literature
Review.................................................................................................................... 16
2.1
Fluid
Mechanics..................................................................................................................... 16
2.1.1
Fluid
Dynamics................................................................................................................ 16
2.1.2
Pressure............................................................................................................................ 16
2.1.3
Temperature..................................................................................................................... 17
2.1.4
Density............................................................................................................................. 18
2.1.5
Viscosity.......................................................................................................................... 19
2.1.6
Specific
Heat................................................................................................................... 21
2.1.7 Law Of Conservation Of Mass....................................................................................... 21
2.1.8 Law Of Conservation Of Linear Momentum.................................................................. 21
2.1.9 Law Of Conservation Of Energy.................................................................................... 22
2.1.10
Aerodynamics................................................................................................................ 22
2.2
Flow Around A
Car............................................................................................................... 22
2.2.1
Drag................................................................................................................................. 23
2.2.2
The Drag
Coefficient....................................................................................................... 25
2.2.3
Lift................................................................................................................................... 25
2.2.4
The Drag
Coefficient....................................................................................................... 26
2.2.5
Dynamic
Pressure............................................................................................................ 26
2.2.6
Pressure
Coefficient......................................................................................................... 26
2.2.7
Boundary
Layer............................................................................................................... 27
2.2.8 Flow Separation On A Car And Wake Creation............................................................. 27
2.3
What Is
CFD?........................................................................................................................ 28
2.3.1 Outline Of Computational Fluid Dynamic Process......................................................... 28
2.3.2 Meshing And Pre-Processing........................................................................................... 29
2.3.3
Numerical
Solver............................................................................................................. 30
2.3.4
Post
Processor.................................................................................................................. 30
2.4
Past
Work............................................................................................................................... 32
3 Chapter Three................................................................................................................................ 37
3.0
Methodology.......................................................................................................................... 37
3.1
Wind Tunnel
Validation......................................................................................................... 37
3.2
Model
Generation................................................................................................................... 38
3.3
Virtual Wind Tunnel
Creation................................................................................................ 39
3.4 Discretisation (Or Meshing) Setup......................................................................................... 40
3.5
Fluent Solver
Settings............................................................................................................ 43
3.6
Turbulence
Modeling.............................................................................................................. 45
3.7
Simulation
Results.................................................................................................................. 45
4 Chapter Four................................................................................................................................. 48
4.0
Discussion............................................................................................................................... 48
4.1
Pressure
Contours................................................................................................................... 48
4.2
Velocity
Contours.................................................................................................................. 50
4.3
Turbulence Intensity
Contours............................................................................................... 51
5 Chapter Five.................................................................................................................................. 53
5.1
Conclusion.............................................................................................................................. 53
5.2
Recommendation..................................................................................................................... 54
References......................................................................................................................................... 55
LIST OF FIGURES
Figure 1-1 Crude oil prices since 1975 [Schmidt 1938] ............................................................... 12
Figure
2-1 (edinburg 1996)
...........................................................................................................
19
Figure 2-2 Forces acting on a vehicle moving on an inclined plane ............................................ 22
Figure 2-3 Vehicle in its natural environment .............................................................................. 32
Figure 2-4 The four main categories of vehicle aerodynamics ..................................................... 33
Figure 3-1 ABU CAR II Model made using solid works ............................................................. 38
Figure 3-2 ABU CAR II Model refined using ANSYS Design Modeler ..................................... 38
Figure 3-3 Virtual wind tunnel around the ABU CAR II model .................................................. 39
Figure 3-4 Triangular Mesh element Around the ABU Car II Model .......................................... 41
Figure 3-5 Shows the dense mesh close to the model and the coarse mesh away from the model
.......................................................................................................................................................
42
Figure 3-6 A section of the prismatic layer (boundary Layer) ..................................................... 43
Figure
3-7
......................................................................................................................................
44
Figure
3-8
......................................................................................................................................
44
Figure
3-9
......................................................................................................................................
44
Figure
3-10
....................................................................................................................................
44
Figure
3-11 Drag Convergence
.....................................................................................................
46
Figure
3-12 Lift Convergence
.......................................................................................................
46
Figure 3-13 Momentum Convergence .......................................................................................... 47
Figure 3-14 Coefficient of Pressure around the Car ..................................................................... 47
Figure 4-1 Pressure Contours of the Car Front ............................................................................. 48
Figure 4-2 Small negative pressure on the front wheel fender ..................................................... 48
Figure 4-3 Pressure Contours of the Car side ............................................................................... 49
Figure 4-4 Pressure Contours of the rear of the car ...................................................................... 49
Figure 4-5 Velocity Contours of airflow over the car................................................................... 50
Figure 4-6 Stream line of airflow over the car .............................................................................. 51
Figure 4-7 Turbulence Intensity Contours of airflow over the car ............................................... 51
NOMENCLATURE
L = Length of the vehicle
W = width of the vehicle
H = Height of the vehicle
A = Frontal area of the vehicle
ρ = Density of the surrounding air
= Coefficient of rolling resistance
= Coefficient of friction
= Coefficient of friction of brake lining
V = Velocity of the vehicle
= Coefficient of drag
M = Mass of the vehicle
g = Acceleration due to gravity
t = time
p = pressure
μ = static viscosity
cp = specific heat capacity
T = temperature
k = coefficient of thermal conductivity
Φ =viscous dissipation f unction
U = free stream velocity
F D = drag force
= static pressure
p = pressure at specific point
This
chapter gives a brief introduction on the project. It includes the
background, the problem statement, the aims and objectives and the
methodology of the project.
1.1 BACKGROUND OF STUDY
The
presence of greenhouse gases in the atmosphere is a natural component
of the climate system and helps to maintain the Earth as a habitable
planet. Greenhouse gases are relatively transparent to incoming solar
radiation, allowing the sun‘s energy to pass through the atmosphere to
the surface of the Earth. The energy is then absorbed by the Earth‘s
surface, used in processes like photosynthesis, or emitted back to space
as infrared radiation. Some of the emitted radiation passes through the
atmosphere and travels back to space, but some is absorbed by
greenhouse gas molecules and then re-emitted in all directions. The
effect of this is to warm the Earth‘s surface and the lower atmosphere.
(Shmidt, 1938)
Water vapor (H2O) and carbon dioxide (CO2) are the two largest contributors to the greenhouse effect. Methane (CH4), nitrous oxide (N2O),
chlorofluorocarbons (CFCs) and other greenhouse gases are present only
in trace amounts, but can still have a powerful warming effect due to
their heat-trapping abilities and their long residence time in the
atmosphere. (Shmidt, 1938)
Without
the greenhouse effect, Earth‘s aver- age temperature would be -0.4°F
(-18°C), rather than the present 59°F (15°C). Concentrations of
greenhouse gases especially carbon dioxide have risen over the past two
hundred and fifty years, largely due to the combustion of fossil fuels
for energy production which has resulted in excessive warming of our
planet, a phenomenon known as Global Warming. This brings about the need
for fuel efficient vehicle that minimize emissions into the atmosphere
(Schmidt 1938).
Figure 1-1 Crude oil prices since 1975 [Schmidt 1938]
The
energy crisis has also generated strong public interest in the fuel
economy of cars. In those countries, where fuel prices were high, even
before the oil embargo of 1973/74 as shown in figure 1.1, good
mileage always has been an important quality of road vehicles.
However the current world energy situation has caused increased
effort in all countries to improve the efficiency of ground
transportation, hence the need for fuel efficient cars.(Shmidt, 1938)
The
above two challenges are the main reasons why the Shell Eco Marathon
competition was founded. Every year, more than 200 teams from over 30
different countries gather, with one unique challenge: design, build,
test and drive the most efficient vehicle. The ultimate goal of the
competition is to produce the most fuel efficient car: That is the one
that travels the longest distance using the least amount of fuel. In
order to be successful in the competition, large effort must be put in
reducing fuel consumption and increasing the overall efficiency of the
car. (Norman, 2015)
1.2 PROBLEM STATEMENT
Traditionally,
aerodynamics is related to airplanes and some (high performance)
automotive applications, where most applications are esthetically
driven. The general interest in Vehicle aerodynamics has mainly been
driven by the Sudden spike in fuel prices and concern of
greenhouse gas emissions hence the need for fuel efficient vehicles,
the same reason why the
Shell
Eco Marathon competition was created. Hence, any team hoping to be
successful in the Shell Eco Marathon competition should pay good
attention to the aerodynamics of their vehicle to achieve good fuel
efficiency. This brings about the need to carry out aerodynamic analysis
of any vehicle design they come up with.
1.3 PRESENT WORK
In
this work, the numerical simulation of incompressible flow was carried
out over the ABU CAR 11 model moving at a speed of 40m/s. Solid Works
was used to create the 3D CAD model of the car. ANSYS Fluent, the
computational fluid dynamics software was used to perform the
computation. All the analysis have been carried out computationally
in the CFD software
―ANSYS
Fluent 15‖ and the CAD modeling in ―Solid Works 2014‖.The analysis was
performed to study the flow behavior of air over the car body. The
analysis incudes the study of pressure and velocity contours that impact
the car body followed by an evaluation of coefficient of drag and lift
in order to analyze possible was to reduce drag.
1.4 AIM AND OBJECTIVE
The
aim of this project is to investigate the flow analysis around the body
the ABU CAR 11 model in order to understand how to minimize the drag
coefficient in real life vehicle problem thereby increasing fuel
efficiency.
The specific objectives are;
i. Produce a CAD model of the ABU CAR 11
ii. Carry out the flow simulation.
iii. Obtain the coefficients of drag, lift and moment.
iv. Obtain pressure and velocity contours
v. Make recommendations on how to reduce drag based on results obtained
1.5 JUSTIFICATION
The three primary factors that influence fuel efficiency are:
• The mass of the vehicle,
• The efficiency of the engine and
• The aerodynamic drag.
The
participants in Shell Eco marathon have little control over the
efficiency of the engine as they are likely to buy from a manufacturer.
This is because the facilities to produce one are not easily available
to them. This leaves them with two major factors within their control:
the mass of the vehicle and the aerodynamic drag. The shape of the
vehicle determines the aerodynamic drag. The shape of the vehicle
determines the shape of the chassis which in turn determines the
heaviest weight of the car. These reasons make the aerodynamic
optimization of vehicle shape a number one priority for any team
participating in shell eco marathon.
1.6 SCOPE
This
should be borne in mind that the scope of the aerodynamic
characteristics being considered is limited to the influence of
aerodynamic drag. However, attention must be drawn to the fact
that drag is not the only aerodynamic phenomenon a car
experiences. This emphasis on drag is timely because of the present day
concern about energy conservation. From a technological point of view,
this focusing of attention also permits depth of treatment, and
increases the possibility of significant technical progress being
made.
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