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.

 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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