drag force analysis of car

Drag Force Analysis of Car

G. H. Raisoni College of Engineering, Nagpur

Department of Mechanical Engineering

B. E. PROJECT

DRAG FORCE ANALYSIS OF CAR

This project is submitted in partial fulfillment of the requirements for the award of

degree of

Bachelor of Engineering in Mechanical Engineering

SUBMITTED BY

Abhishek Kumar Ravishek Kumar Ashwin S Tembhurney Abhishek A Gomase

GUIDEProf. R. M. Metkar


2005-2006

DEPARTMENT OF MECHANICAL ENGINEERING

G. H. RAISONI COLLEGE OF ENGINEERING, NAGPUR


G. H. RAISONI COLLEGE OF ENGINEERING, NAGPUR

DECLARATION

This project titled “Drag Force Analysis of Car” is our own work carried out under

the guidance of Prof. R. M. Metkar at G. H. Raisoni College of Engineering, Nagpur.

This work in the same form or in any other form is not submitted by us or by anyone

else for award of any degree.

Abhishek Kumar Ravishek Kumar

Ashwin S Tembhurney Abhishek A Gomase


CERTIFICATE

This to certify that the project titled “Drag Force Analysis of Car ” is a bonafide

work done by Abhishek Kumar, Ravishek Kumar, Ashwin S Tembhurney and

Abhishek A Gomase and is submitted to the Rashtrasant Tukdoji Maharaj Nagpur

University, Nagpur in partial fulfillment of the requirements for the degree of

Bachelor of Engineering in Mechanical Engineering.

Prof. R. M. MetkarGUIDE


CERTIFICATE

Forwarded herewith the project titled “Drag Force Analysis of Car” by Abhishek

Kumar, Ravishek Kumar, Ashwin S Tembhurney and Abhishek A Gomase student of

this college, in partial fulfillment of the requirements of degree of Bachelor of

Mechanical Engineering

Professor and Head Principal



G. H. RAISONI COLLEGE OF ENGINEERING,

NAGPUR.

ACKNOWLEDGEMENT

It is really a matter of great pleasure to acknowledge the invaluable guidance,

enormous assistance and excelled cooperation which was extended to us for the

smooth completion of our project.

We gladly take the opportunity to regard thanks to our guide Prof. R. M.

METKAR for inspiring us and giving his valuable advice and excellent guidance in

this project work.

We would like to thank Prof. G. R. Boob, lecturer, G. H. Raisoni College of

Engineering, Nagpur, for his kind support and guidance, without which this project

would not have been possible.

We would also like to give our sincere thanks to Mr. Surjeet Singh ,Senior

Manager, Seva Automotives, Nagpur.

We would like to thank all others who have helped us directly or indirectly in

making this project. Last but not the least; we would like to thank our parents for

their never ending support and guidance.

This chapter must be closed with a word of praise and gratitude toward Dr. S.

G. Tarnekar, Principal, G.H.R.C.E., who provided all the necessary facilities and

requirement.

PROJECTEES

Abhishek Kumar Ravishek Kumar

Ashwin S Tembhurney Abhishek A Gomase


ABSTRACT

To save the energy and to protect the Global environment, fuel consumption

reduction is a primary concern of the modern car manufacturers. Drag reduction is

essential for reducing the fuel consumption. Designing a vehicle with a minimized

Drag resistance provides economical and performance advantages. Decreased

resistance to forward motion allows higher speed for the same power output, or lower

power output for the same speed. The shape is an important factor for drag reduction.

To design an efficient shape of the car that will offer a low resistance to the forward

motion, the most important functional requirement today is the low fuel

consumption. The resistance, termed as the drag force (or the drag coefficient in non

dimensional terms), is a strong function of the shape of the car. This suggests it is

important how the fluid particles move about the car and how fast they move along

their path.

The main intention behind this project is to compute the Drag co-efficient,

Drag force and moments on low mass vehicle by using CFD software (computational

fluid dynamics) , CFD Tutor1.1.


INDEX

CHAPTER

1.0 Introduction

2.0 Literature Review

3.0 Aim of The Project

4.0 Regimes of External Flow

5.0 Profile Drag

6.0 Minimizing Drag on a Low Mass Vehicle

6.1 Expression of Drag Force

6.2 Shape of the Vehicle’s Body

7.0 Stream Lined and Bluff Body

8.0 Drag

8.1 Components of Drag

9.0 Thrust vs. Speed of Car

10.0 Computational Fluid Dynamics (CFD)

10.1 Introduction

10.2 Applications of CFD

11.0 Analysis

11.1 Geometry Generation and the

Co-ordinates of Maruti 800 in PRO/E Wildfire

12.0 Analysis in CFD TUTOR 1.1

12.1 Pre-Processing operation

12.2 Processing operation

12.3 Post Processing operation

12.4 Calculations and Result

13.0 Conclusion and Future Scope

14.0 References

15.0 Appendix


List of Tables

List of Figures

Table No. Details

1 CD for various objects

2 Co-ordinates of Maruti 800

3 CD for various Mach numbers

Fig. No. Details

1 Flow Regimes around an immersed body

2 Friction Drag Airflow Orientation

3 Pressure Drag Airflow orientation

4 Shape of Vehicle’s Body

5 Stream-lined Body and Bluff Body

6 CD of drag Vs angle between separating streamlines

7 Components of Drag

8 Cars at Different Speeds

9 2D sketch of Maruti 800

10 Grid Generation for Maruti 800

11 Pressure distribution along the body of car

12 Temperature Distribution along the car

13 Velocity Distribution in X-direction of the Car

14 Velocity Distribution in Y-direction of the Car

15 Pressure Distribution along the shape of the car

16 Velocity Distribution in X-direction


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ABBREV

ABBREVIATION

Symbols Description

CD Co-efficient of Drag

DF Drag Force (N)

A Projected frontal area of the vehicle (mm2)

ρ Density of air (Kg/m3)

V Speed of the vehicle relative to the air (m/s)

Pmax Maximum pressure on the shape of car (Pa)

Pmin Minimum pressure on the shape of car (Pa)

∆P Change in Pressure (Pa)

CFD Computational Fluid Dynamics


1.0 INTRODUCTION Embracing the 21st century in stride, virtually all manufacturers have adopted

some form of computer aided design, Engineering, Manufacturing and Analysis. It is

a common belief that they can stay ahead by continuously introducing new products

that are differentiated by the latest Technology revolution, innovative designs, higher

functionality and superior quality. The best technology to integrate expertise

knowledge and companies unique practice is the CAD/CAM and analysis software

packages; a comprehensive suite of solution to meet the present day demand.

In general term CAD/CAM means computer assistance whilst a designer

converts his ideas and knowledge into a graphical model and graphical model into

physical model. After that he analyses the physical model to meet the Environmental

conditions.

The automotive industry is a large user of commercial CFD packages. The

advantage of CFD results in better designs and reduced time for the automotive

manufacturers. CFD is not only used to improve the aerodynamics of vehicles, but

also for the optimization of domains such as engine cooling, brake cooling, airbags,

lighting and fuel system. During the development of new vehicles, understanding the

flow phenomena and how aerodynamic forces are influenced by changes in body

shape are very important. A large variety of complex flow properties such as three-

dimensional turbulent boundary layer on the body surfaces, longitudinal vertices

induced by three-dimensional separation, recirculation flows caused by separation

and the ground plane boundary layer and their interaction are important to be

understood. However, using CFD is a good way for designers to obtain results in a

shorter time.

The job of the aerodynamics engineer is to create a body shape that

maximizes the force in direction of the ground, the down force, and minimizes the

force that opposes the movement, the drag force.

The CAD software PRO/E Wild Fire is used to design the outer body shape

by finding out the co-ordinates of the body. The mesh generation and analysis to find

the Co-efficient of Drag is done by using the CFD analysis software CFD Tutor 1.1

designed and created by Zeus, Aerospace Department, Indian Institute of

Technology, Mumbai.


Drag Force analysis of car comprises of following steps:

1) Geometric modeling in 2D by importing the image of car in PRO/E Wildfire

and finding out the co-ordinates of the car.

2) The co-ordinates of car are used in CFD Tutor 1.1 to draw the image of car

and then analyze the car to find out the CD by giving boundary conditions i.e.

Pressure, velocity, Density of air and Atmospheric temperature.

3) Calculate the Drag Co-efficient by using the values obtained from analysis.

One of the objectives of this project is to conceive a body which is optimized

to have good performance. The project is focused on the outer body shape of the car.

The CFD tools have been used to assess the quality of the design. The main purpose

behind this project is to analysis the shape of simple car in 2D and find out the drag

co-efficient which will help to modify the car shape or can help in design of new car

aerodynamically.


2.0 LITERATURE REVIEW

The Drag co-efficient of the Vehicle’s body is evaluated by numerical

computations performed with commercial CFD software, Finite Volume based

solver, using the Navier-Stokes Equation.

Indeed, it is worth noticing that the changes on the drag when changing the

shape deal with pressure force. Moreover as only 30% of the Drag Co-efficient

depends on the front of the shape, the slanted surfaces and vertical base surface of the

rear end will contribute strongly to pressure drag.

A way to have a good working definition of what CFD is to break down the

word. “CFD is the acronym of Computational Fluid Dynamics. Computational means

having to do with mathematics, computation and Fluid Dynamics refers to the

dynamics of things that flow.”

So, CFD is a computational technology that enables us to study things that

flow. CFD not only predicts fluid flow behavior, but also the transfer of heat, mass,

phase change, chemical reaction, mechanical movement and stress or deformation of

related solid structures.

“The Drag busters” by R. Hendrickson, Grumman, with Dino Roman

and Dario Rajkovic, has given the importance of drag. Drag is the heart of

aerodynamic design. The subject is fascinatingly complex. All aerodynamicists

secretly hope for negative drag. New design that employ advanced computational

aerodynamics methods are needed to achieve vehicles with less drag than current

vehicles.

“Aerodynamic shape optimization in automotive Industry” by Fredrique

Muyl, Laurent Dumas and Vincent Herbert has given the important aspects of the

aerodynamic shape optimization tool for complex industrial flow. For each

evaluation required by the optimizer, The Navier-Strokes equations are solved with a

commercial CFD code on an unstructured mesh surrounding the shape to optimize.

“Reducing drag forces in future vehicles”, project in the course road

vehicle and aerodynamic design, MTF 235, AUTUMN 2002 by Alexander Diehl,

Jose nuno Lopes, Rui Miranda, Chalmers university of technology, has explained

the relationship between drag force and speed of the car, drag force and change in

drag coefficient and several ways to reduce the drag co-efficient of a vehicle.


The investigators who are working on this project will learn how to modify

car surface to reduce the drag and moment on the car body shape without changing

the original structural frame of the vehicle. In turn, the principal investigator will

include the new information from his research in his lecture material of fluid

mechanics.

Industrial Impact: Aerodynamic forces on low mass vehicles and trucks are

now the subjects of much interest not only to car manufacturers but also to the

government since they strongly affect fuel economy and safety. Thus, it would be

plausible to apply the techniques obtained from this project to other problems such as

drag reduction for trucks.


3.0 AIM OF THE PROJECT

Decreasing the fuel consumption of road vehicles, due to environmental and

selling arguments reasons, concerns car manufacturers. Consequently the

improvement of the aerodynamics of car shapes, more precisely the reduction of their

drag coefficient, becomes one of the main topics of the automotive research sectors.

Designing a vehicle with a minimized Drag resistance provides economical and

performance advantages. Decreased resistance to forward motion allows higher

speeds for the same power output, or lower power output for the same speeds.

The main aim for reducing drag resistance is:

Fuel consumption reduction and

Performance increasing.


4.0 REGIMES OF EXTERNAL FLOW

Consider the external flow of real fluids. The potential flow and boundary

layer theory makes it possible to treat on external flow problem as consisting broadly

of two distinct regimes, that immediately adjacent to the body’s surface, where

viscosity is predominant and where frictional forces are generated, and that outside

the boundary layer, where viscosity is neglected but velocities and pressure are

affected by the physical presence of the body together with its associated boundary

layer. In addition, there is the stagnation point at the front of the body and there is the

flow region behind the body (known as the wake). These flow regimes are shown in

Figure 1.

Fig.1: Flow Regimes around an immersed body

The wake starts from the points ‘S’ at which the boundary layer separation

occurs. Separation occurs due to adverse pressure gradient, which combined with the

viscous forces on the surface produces flow reversal, thus causes the stream to detach

itself from the surface. The same situation exists at the rear edge of a body as it

represents a physical discontinuity of the solid surface.

The flow in the wake is thus highly turbulent and consist of large scale

eddies. High rate energy dissipation takes place there, with the result that the pressure

in the wake is reduced. A situation is created whereby the pressure acting on the

body (stagnation pressure) is in excess of that acting on the rear of the body so that

resultant force acting on the body in the direction of relative fluid motion exerts. The

force acting on the body due to the pressure difference is called pressure drag.


5.0 PROFILE DRAG


Any object that moves through a fluid (water/air) can get a decrease in form

drag by streamlining. Automobiles are streamlined, which translates (allows) better

gas mileage; there is less drag so less fuel is required to "push" the car forward.

Buses, vans, and large trucks are less streamlined, and this is the reason why they use

more fuel than smaller streamlined cars (weight is another reason).

The drag is a resistance force. This force works to slow the forward motion of

an object, including planes. There are mainly two types of drag: Pressure drag and

friction drag. These drag types develop around the shape of the body, the smoothness

of the surfaces, and the velocity of the plane. The total drag on the body, often called

profile drag is therefore, made up of two contributors namely the pressure drag and

the friction drag. The drag forces are the opposite of thrust. If the thrust force is

greater than the drag force, the vehicle goes forward, but if the drag force exceeds the

thrust, the vehicle will slow down and stop.

The friction drag is sometimes also called the skin friction drag. The force on

the body acting in the direction of relative motion due to fluid shear stress is known

as Frictional drag. Thus in external flow the immersed body is subjected to functional

drag over its entire surface. Fig.2 shows the situation where air flowing along a

surface will create lot of friction drag. There is a large fast-moving air next to the

non-moving surface. In contrast, there will be little pressure drag because there is

very little frontal area for anything to push against.

Fig.2: Friction Drag Airflow Orientation

The form drag, or pressure drag as it is sometimes called, is directly related to

the shape of the body of the vehicle. Fig.3 shows the situation where air flowing

along a surface will create lots of friction drag.


Fig.3: Pressure Drag Airflow orientation

Thus,

Total drag = Pressure drag + Friction drag

The relative combination of pressure drag and friction drag to the profile drag

depends upon the shape of the body and its orientation with respect to the flow.


6.0 MINIMIZING DRAG ON A LOW MASS VEHICLE (CAR)

There are several ways to reduce the Drag Coefficient (CD) of a vehicle. The

vehicle’s global shape has the most direct influence in the final value of CD. Still,

improvements in details like the rearview mirrors, underbody, or the use of some

particular devices may contribute to a lower final CD.

6.1 EXPRESSION OF DRAG FORCE

The Drag force (DF) for a moving vehicle is given by the following expression:

DF = 1/2 A ρ CD V2

Where

CD is the drag coefficient

A is the projected frontal area of the vehicle

ρ is the density of air

V is the speed of the vehicle relative to the air

This equation shows that to calculate drag we need to know three things: CD,

the drag coefficient; A, the frontal area of vehicle/car, and V, the speed of air past the

vehicle. This equation shows important point-aerodynamic forces are proportional to

the square of the speed. That means you quadruple the drag or lift when you double

the speed. Since speed is never the item that is pretended to be decreased and the

density of air is not even possible to change, the aerodynamic resistance can only be

reduced or minimized by manipulating the vehicle’s design characteristics, obtaining

lower Drag coefficients (CD), or even reducing the vehicle’s frontal area.


6.2 SHAPE OF THE VEHICLE’S BODY

The vehicle’s global body shape states the average aerodynamic performance,

so it is the most important design feature. The main requirement is that the shape

should maintain attached flow over most of the surface. This is accomplished by

having a streamlined shape. The most efficient shapes are the simple ‘teardrop’ or the

airfoil based one.

Fig.4: Shape of Vehicle’s Body

Unfortunately, these two body shapes are very hard to put in practice because

they have very little or sometimes non acceptance by the customers. Furthermore,

these shapes tend to cause obstacles to some functional aspects of the vehicles, like

storing space, and dynamic stability.


7.0 STREAM LINED BODY AND BLUFF BODY


A bluff body is a body where the boundary layer separates permanently from

the surface. This is in contrast to a streamlined body where the boundary layer either

does not separate, or possibly separates temporarily, and reattaches further

downstream.

A stream lined body is defined as that body whose surface coincides with the

stream lines, when the body is placed in a flow. In this case the separation of flow

will take place only at the trailing edge (or rearmost part of the body). Though the

boundary layer will start at the leading edge, will become turbulent from laminar, yet

it does not separate up to the rearmost part of the body in case of stream-lined body.

Bluff body is defined as that body whose surface does not coincide with the

streamlines, when placed in a flow, then the flow is separated from the surface of the

body much ahead of its trailing edge with the result of a very large wake formation

zone. Then the drag due to pressure will be very large as compared to the drag due to

friction on the body. Thus, the bodies of such a shape in which the pressure drag is

very large as compared to friction drag are called bluff bodies.

Fig.5: Stream-lined Body and Bluff Body

When the drag is dominated by viscous drag, we say the body is streamlined,

and when it is dominated by pressure drag, we say the body is bluff. Whether the

flow is viscous-drag dominated or pressure-drag dominated depends entirely on the

shape of the body. A streamlined body looks like a fish, or an airfoil at small angles

of attack, whereas a bluff body looks like a brick, a cylinder, or airfoil at large angles

of attack. For streamlined bodies, frictional drag is the dominant source of air

resistance. For a bluff body, the dominant source of drag is pressure drag.


Since flow separation depends on many parameters in addition to pressure

gradient, bluff body flows are often somewhat unpredictable. There can be sudden

changes in flow pattern for relatively minor changes in geometry or orientation (or,

as we shall see later, Reynolds number). It is also possible to get flows in which two

relatively stable states exist; the flow can switch between them as a result of minor

external effects, either on a random or a periodic basis. This may sometimes involve

reattachment of flow. After the boundary layers have separated, they are known as

free shear layers, or sometimes dividing or separating streamlines.

The region of flow outside the free shear layers is known as the free stream,

while that between them is the wake. The part of the body upstream of the separation

points, exposed to the free stream flow is known as the forebody. That after them,

exposed to the wake, is the afterbody or base.


8.0 DRAG

For bluff bodies where the drag is mainly due to direct stresses, the drag

coefficient is defined in terms of a dimension normal to the flow. This is in contrast

to streamlined bodies where the drag is mainly due to shear stress, where a dimension

parallel to the flow is used. This is discussed further in the Appendix on drag

coefficients and their definitions.

The drag is sometimes divided into forebody drag, due to the pressure

distribution around the front, and base drag, due to that round the back. This is useful

because, by and large what goes on in the wake does not depend to any extent on the

forebody, provided separation occurs at the same place, and similarly the flow over

the forebody is not influenced much by changes in the base region.

Typical values for drag co-efficient are:

Table 1 shows the CD for various objects

Circular cylinder normal to stream 0.35 to 1.2, depending on

Reynolds number

Flat plate normal to stream 2.0

Rectangular section 0.9 to 3, depending on aspect

ratio

Sphere 0.1 to 0.4 depending on

Reynolds number

Disk normal to stream 1.2

Cube 1.1

Saloon car 0.35

Articulated container truck 0.7

A simple correlation that seems to hold for a variety of two dimensional

shapes is that the drag coefficient increases as the angle between the separating shear

layers increases.


Fig.6: Co-efficient of drag versus angle between separating streamlines

For example, a 90 angle with its apex upstream has a CD of about 1.7, a flat

plate (180) is about 2.0, and an angle with its apex downstream (270) is about 2.1.

Further examples are given in the following graph; a similar relationship seems to

hold for axially symmetric bodies - cones, disks, spheres.

8.1 COMPONENTS OF DRAG

There are mainly four components of drag. These are:

1. Driving Force

2. Resistance Force

3. Weight

4. Lift/Reaction Force

Fig.7: Components of Drag


1. Thrust/Driving Force: - Driving Force is the Force Developed by the motion

of the vehicle in forward Direction.

2. Drag/Resistance Force: - Resistance Force is the resistance developed by the

motion of the air in the opposite direction of the motion of the vehicle.

3. Weight: - Weight is nothing but the weight of the vehicle itself, acting in the

downward direction.

4. Lift/Reaction Force: - Lift is upward force acting on the vehicle. It acts on

both the front and rear wheels of the vehicle. It is induced due to the vortices

created on the back of the vehicle and it is the reason that the lift on the rear

wheel is more than the lift on the front wheel.


9.0 THRUST vs. SPEED OF CAR

When we start moving in a car the resulting force is forward. In the following

figure we assume that the car’s engine will produce constant thrust, no matter what

its speed.

Fig.8: Cars at Different Speeds

Once the drag vector length equals the thrust vector line length, there is no

more acceleration. The car has reached “equilibrium” speed. We’ve just learned a

new term, equilibrium. Equilibrium exists when all force vectors are balanced. They

cancel each other out.

Note that at 30 MPH the drag vector is only 1/4 the length of the drag vector

at 60 MPH. We just want to reinforce the facts that drag increases as the square of

the velocity.


10.0 COMPUTATIONAL FLUID DYNAMICS (CFD)


10.1 INTRODUCTION

A way to have a good working definition of what CFD is to break down the

word. “CFD is the acronym of Computational Fluid Dynamics. Computational means

having to do with mathematics, computation and Fluid Dynamics refers to the

dynamics of things that flow.”

So, CFD is a computational technology that enables you to study things that

flow. CFD not only predicts fluid flow behavior, but also the transfer of heat, mass,

phase change, chemical reaction, mechanical movement and stress or deformation of

related solid structures.

Computational Fluid Dynamics or simply CFD is concerned with obtaining

numerical solution to fluid flow problems by using computers. The advantage of

high-speed and large-memory computers has enabled CFD to obtain solutions to

many flow problems including those that are compressible or incompressible,

laminar or turbulent, chemically reacting or non-reacting. Computational Fluid

Dynamics (CFD) is the science of predicting fluid flow, heat transfer, mass transfer,

chemical reactions, and related phenomena by solving the mathematical equations

which govern these processes using computational methods.

CFD is the art of replacing the differential equation governing the Fluid Flow,

with a set of algebraic equations (the process is called discretization), which in turn

can be solved with the aid of a digital computer to get an approximate solution. The

well known discretization methods used in CFD are Finite Difference Method

(FDM), Finite Volume Method (FVM), Finite Element Method (FEM), and

Boundary Element Method (BEM). FDM is the most commonly used method in CFD

applications.

The benefits of using CFD can be summarized in three points:

Insight: There are many devices and systems that are very difficult to

prototype. Often, CFD analysis shows parts of the system or phenomena happening

within the system that would not otherwise be visible through any other means. CFD

gives a means of visualizing and an enhanced understanding of the various designs.


Foresight: Because CFD is a tool for predicting what will happen under a

given set of circumstances, it can answer many ‘what if?’ questions very quickly. We

give it variables. It gives us outcomes. In a short time, we can predict how the design

will perform, and many variations may be tested until you arrive at an optimal result.

All of this is done before physical prototyping and testing. The foresight we gain

from CFD helps us to design better and faster.

Efficiency: Better and faster design or analysis leads to shorter design

cycles. Time and money are saved. Products get to market faster. Equipment

improvements are built and installed with minimal downtime. CFD is a tool for

compressing the design and development cycle.

10.2 APPLICATIONS OF CFD

CFD is interdisciplinary cutting across fields of aerospace, mechanical, civil,

chemical, electrical engineering as well as physics and chemistry. CFD has been

widely used in industry in the past decade. It is certainly fun for fluids enthusiasts,

but where exactly can CFD be applied - Following are the areas of applications of

CFD.

Automobile and Engine

Aerodynamics, Engines, Turbochargers, Intake/Exhaust Heating/Cooling

Systems, Brakes etc.

Industrial Manufacturing

Aerospace, Aerodynamics. Gas Turbines, Rockets etc.

Mechanical

Pumps, Compressors, Heat Exchangers, Furnaces, Nuclear Reactors etc.

Chemical

Mixers (multiphase), Chemical Reactors, Separators, Boilers, Condensers etc.

Environmental Engineering

Weather prediction, River and Tidal flows, Wind and Water-borne pollution,

Fire and Smoke spread, Wind loading etc.


Physiological

Cardiovascular flows (Heart, major vessels), Flow in Lungs and breathing passages

etc.

Naval Architecture

Ship building etc.

Others

Glass, Steel and Textile manufacturing, Food processing etc.


11.0 GEOMETRY GENERATION USING PRO/E WILDFIRE SOFTWARE

11.1 2D SKETCH OF MARUTI 800 USING PRO/E WILDFIRE

We have made the scaled 2-D model of Maruti 800 with its actual dimensions

by using the CAD software. We have taken the jpg. Image of the Maruti 800 and

imported this image in the Pro/E wildfire software. We know the outer dimensions of

the Maruti 800. After giving the outer dimensions, we have found out the co-

ordinates of the external shape of the Maruti 800. After finding out these co-

ordinates, we can use these co-ordinates in the CFD software to draw the external

shape of the vehicle for the analysis.

The overall dimensions of the Maruti 800 are:-

Overall Length: 3335 mm

Overall Width: 1440 mm

Fig.9: 2D sketch of Maruti 800


CO-ORDINATE GENERATION OF MARUTI 800

Table 2: Co-ordinates of Maruti 800

S. No. Co-ordinate in X direction

Co-ordinate in Y direction

1 102.26 227.272 40.25 389.173 16.12 491.714 102.57 530.915 74.43 644.516 112.40 724.997 327094 807.418 809.75 940.549 878.99 981.7110 1354.43 1348.6311 1400.94 1384.8012 1788.53 1426.1513 2444084 1436.4814 2801.42 1410.6415 2915.12 1322.7916 3194.18 997.2217 3271.70 862.8518 3287.33 661.0719 3297.19 619.6720 3336.62 592.0721 3340.56 542.7922 3310.99 454.0823 3301.13 377.2024 3253.82 341.7125 2991.63 298.3426 2367.53 264.5127 1374.39 233.4828 362.63 227.27


12.0 ANALYSIS IN CFD TUTOR 1.1

12.1 PRE- PROCESSING IN CFD TUTOR 1.1


Fig. 10: Grid Generation for Maruti 800

12.2 PROCESSING OPERATIONS IN CFD TUTOR 1.1

Fig. 11: Pressure distribution along the body of car


Fig.12: Temperature Distribution along the car

Fig.13: Velocity Distribution in X-direction of the Car


Fig.14: Velocity Distribution in Y-direction of the Car


12.3 POST PROCESSING OPERATION IN CFD TUTOR 1.1

Fig.15: Pressure Distribution along the shape of car

Fig .16: Velocity Distribution in X-direction


12.4 CALCULATION

Drag Force, DF = 1/2 A ρ CD V2 ----------------------------------------------------- I

Pressure Drag, P = ∆P * A ------------------------------------------II

Equating Equation I and II, we get

∆P * A = 1/2 A ρ CD V2

Therefore, CD = 2 ∆P/ ρ V2 -------------------------------------------III For Mach No. = 0.05 (60 Km/hr) Pmax = 1.0669 *105

Pa

Pmin = 1.0086* 105 Pa ∆P= 5830 Pa

ρ = 1.125 kg/m3

Vmax = 1.246 m3/ s

Put the values in equation III, we get CD = 0.667

Table 3: CD for various Mach number

S. No. Mach No.

Pmax (Pa) Pmin (Pa) ∆P (Pa) Vmax (m/sec)

CD

1 0.05 1.0669*105 1.0086*105 5830 1.246*102 0.667

2 0.066 1.078* 105 1.009* 105 6900 1.314*102 0.71

3 0.083 1.081*105 1.014*105 6654 1.30*102 0.7

4 0.1 1.0869*105 1.00864*105 7826 1.246*102 0.896

Thus, the Drag Co-efficient are not constant ,but depends on a number of factors, including; Shape of object, the orientation relative to the flow and the fluid’s viscosity, mass, density, flow speed and object size.


13.0 CONCLUSION AND FUTURE SCOPE

The aerodynamic design of vehicles is an area where a lot of improvements

will appear in the near future, in concern of drag reduction. The guidelines pointed

out in the text are of a general nature that can be implemented in most modern road

going vehicles; Smooth vehicle shape, rounded corners, High rake angle for the

windscreen, Tapered rear end, Minimized body seams, Optimized rear view mirrors

and Smooth underbody. Wheel sides, wheel covers kept smooth and minimizing gap

between wheelhouse and wheels.

The aerodynamics of road vehicles have been described in order to get

notions about how to reduce drag resistance, and sometimes even theoretically ideal

techniques have been recommended. However, we design an automobile, have to

deal with a whole lot of other performance, functionality and styling issues which

sometimes, and not so few, still tend to rule when meeting incompatibilities with

aerodynamic ones.

We have completed successfully the analysis of Maruti 800 in 2-D by using

CFD software CFD Tutor 1.1. By taking in account the boundary conditions;

velocity, pressure, density of air and the frontal area of the car, we can design the

new shape of the car in 2D as well as in 3D in the future. Thus we will be able to

produce the vehicle’s body shape with optimum frontal area that will offer less

resistance to the air moving in the opposite direction.

Some of these incompatibilities are very hard to overcome since some of

those non aerodynamic characteristics of a vehicle often have an exceptionally

narrow range of possible alternatives. Styling may be the most flagrant example:

Consumers/buyers always seek for a certain ‘look’. This concept is today very

different from the aerodynamically ‘ideal’ car.

Keeping to these guidelines we should make it possible to have commercial

vehicles with a CD value between 0.20 and 0.25 in the coming future.


14.0 REFERENCES

Paper: Inchul Kim and Xin Geng, [2002], “Optimization of Body Shape

through Computation of Aerodynamic Forces on Low Mass Vehicle

(LMV)”, Department Of Mechanical Engineering, University Of

Michigan-Dearborn, Dearborn, Mi 48128.

Paper: Alexander Diehl, Jose Nuno Lopes, Rui Miranda, Christoffer

Mursu Simu and John Viji, autumn 2002, “Reducing Drag Forces

in Future Vehicles”, Department of Thermo and Fluid Dynamics,

Chalmers, University of Technology.

Paper: Frederque Muyl, Laurent Dumas and Vincent

Herbert, [October

2001], “Hybrid method for Automotive Shape Optimization in

Automotive Industry, PSA Peugeot Citroen, Centre technique,

Veliz Villacoublay, France

Book: Fluid Mechanics By John F Douglas, Janusz M Gasiorek and John

A Swaffield, Published by Pearson Educations.

Websites: www.engin.umd.umich.edu/ceep/tech_day

www.maruti800.marutiudyog.com

www.princeton.edu/~asmits/Bicycle_web/blunt.html

Project Website: www.dragforceanalysis.tk

http://www.dragforceanalysis.tk/

http://www.princeton.edu/~asmits/Bicycle_web/blunt.html

http://www.maruti800.marutiudyog.com/

http://www.engin.umd.umich.edu/ceep/tech_day


15.0 APPENDIX

Participating Certificates during State Level, National Level and International

Level Paper Presentation.

Website of Drag Force Analysis of Car of this Project designed by Mr.

Ravishek Kumar.

http://www.ravishek.tk/

http://www.ravishek.tk/

http://www.dragforceanalysis.tk/

drag force analysis of car

Documents