A Seminar Report on

AERODYNAMICS IN CARS
Submitted in partial fulfillment of the requirements
FOR THE DEGREE OF
BACHELOR OF TECHNOLOGY
IN
MECHANICAL ENGINEERING

Under the Guidance of: Submitted by:

Dr. B.L. Salvi Name: Hitesh Kumar Saini
Assistant Professor Enrollment no: 2016/CTAE/143
Department of Mechanical Subject Code: ME-427
Engineering B.Tech Final Year ME

Session 2019-2020
DEPARTMENT OF MECHANICAL ENGINEERING
COLLEGE OF TECHNOLOGY AND ENGINEERING
MAHARANA PRATAP UNIVERSITY OF AGRICULTURE AND TECHNOLOGY, UDAIPUR, RAJASTHAN
 ACKNOWLEDGMENT

It gives me great pleasure to present my seminar report on “Aerodynamics in

cars”. No work, however big or small, has ever been done without the contributions of
others.

It would be a great pleasure to write a few words, which would although not
suffice as the acknowledgment of this long-cherished effort, but in the absence of
which this report would necessarily be incomplete. So these words of acknowledgment
come as a small gesture of gratitude towards all those people, without whom the
successful completion of this project would not have been possible.

I would like to express deep gratitude towards Dr. S. Jindal, Head. Department
of Mechanical Engineering CTAE Udaipur & Dr. B. L. Salvi, Assistant Professor,
Department of Mechanical Engineering CTAE Udaipur who gave me their valuable
suggestions, motivation and the direction to proceed at every stage. They are like a
beam of light for us. Their kind guidance showed us the path of life and is
unforgettable. I extended towards their valuable guidance, indispensable help, and
inspiration at times in appreciation I offer them my sincere gratitude.

Last but not least I would like to thank the Department of Mechanical
Engineering, CTAE, Udaipur for providing me with the facilities to the lab, and all staff
members of the communication lab, it would have been impossible for me to complete
my report without their valuable guidance & prompt cooperation.

Hitesh Kumar Saini

B.Tech Final Year
Mechanical Engineering

i
 ABSTRACT

When objects move through air, forces are generated by the relative motion
between the air and surfaces of the object. Aerodynamics is the study of these forces,
generated by the motion of air, usually aerodynamics are categorized according to the
type of flow as subsonic, hypersonic, supersonic etc.

It is essential that aerodynamics be taken in to account during the design of cars

as an improved aerodynamics in car would attain higher speeds and more fuel
efficiency. For attaining this aerodynamic design the cars are designed lower to the
ground and are usually sleek in design and almost all corners are rounded off, to ensure
smooth passage of air through the body, in addition to it a number of enhancements
like spoilers, wings are also attached to the cars for improving aerodynamics. Wind
tunnels are used for analyzing the aerodynamics of cars, besides this a number of
software‟s are also available now days to ensure the optimal aerodynamic design.

ii
 CONTENTS

Acknowledgement……….………………………….………………….……….i
Abstract………………………………………………………………………...ii
Contents………………………………………………………………….…….iii
1. Introduction…………………………………………………………………...1
2. History And Evolution Of Aerodynamics……………………………….…...3
3. Aerodynamic Forces On A Body………………………………………….....6
4. Study Of Aerodynamic Forces On Cars………………………………….......9
5. Aerodynamic Devices…………………………………………………….…..16
6. Methods For Evaluating Aerodynamics In Cars……………………………...27
7. Aerodynamic Design Tips………………………………………………….…31
8. Conclusions……………………………………………………………………32
References………………………………………………………………….....33

iii
Chapter 1:

INTRODUCTION

Aerodynamics is the study of how gases interact with moving object. Two basic
aerodynamics forces are drag and lift, drag is the force air exerts against a car as it
moves while lift is the perpendicular force. Lift includes both positive lift that‟s the
flying kind and negative lift and that‟s downforce.

Air moves in a very similar way to liquid, we just can‟t see it. If we think about it
every time we drive, we are practically swimming though an endless air ocean. Air
obliviously is not as dense as liquid but it‟s still touching stuff so there‟s friction when
something moves through it and that makes the drag probably the most important
aerodynamic factor that we have to consider.

Drag is basically a thing velocity squared multiplied by its drag coefficient and
its frontal area. Drag coefficient depends on a lot of factors some of which are an object
overall shape, surface roughness and speed. Brick has an awful of drag coefficient of 1
while a drop, the most aerodynamic shape there is, has a drag coefficient of about 0.05.

In very early days of automobile manufacturer really didn‟t have to care about its
shape because cruising speed barely got up to 45km/h, early racer quickly realized
stream lining their car going to make it a way better to going fast. Because of that
velocity squared part of the equation drag increases significantly, the faster we go.

Fast moving non aerodynamic car, air going to pile up in front of it and create a
area of high pressure and at the back a low pressure air pocket forms and create a
pressure differential so not only there is frictional drag now there is another force trying
to drag the car backwards. All this makes drag a really big factor in determining fuel
efficiencies and top speed. A reduction in drag coefficient from 0.30 to 0.25 would
increase fuel economy by about a mile a gallon. By the same reason electric car go
further on charge the more aerodynamic it is.

Now that we are regularly cruising at speed 100km/h we got a new focus on fuel
efficiency or battery range.

Production car designers try to get the lowest drag coefficient possible. Most

1
modern cars have a drag coefficient somewhere between 0.25 and 0.35 and with SUVs‟
and trucks somewhere around 0.30 and 0.40. The electrical tesla model-x is super sleek
cross over with one of the lowest drag coefficient of any production car, i.e. 0.24.

F1 cars got a drag coefficient of about 0.7 that‟s more than a minivan. F1 cars
and most race cars are designed mostly with lift in mind. Traction and grip are just as
important to fast lap times as speed and power. Turns out keeping a car from flying off
the ground helps improve grip and pressing down on tires with negative lift; downforce,
improves grips even more, downforce alone creates a ton of drag but the trade-off is
worth it because without all that downforce F1 cares would still be spinning their tire at
160km/h and with extra force pressing toward tires they get increased lateral grip for
better cornering speed. A heavy car could achieve the same result but it wouldn‟t able to
accelerate or corner as the light ones.

Aerodynamics have wide range of applications mainly in aerospace engineering,

then in the design of automobiles, prediction of forces and moments in ships and sails, in
the field of civil engineering as in the design of bridges and other buildings, where they
help to calculate wind loads in design of large buildings.

Fig.1.1-Interaction of moving air with car.

(https://mechanixillustrated.technicacuriosa.com/2017/03/04/an-introduction-to-
automobile-aerodynamics/)

2
Chapter 2:

HISTORY & EVOLUTION OF AERODYNAMICS

Ever since the first car was manufactured in early 20th century the attempt has
been to travel at faster speeds, in the earlier times aerodynamics was not a factor as the
cars were traveling at very slow speeds there were not any aerodynamic problems but
with increase of speeds the necessity for cars to become more streamlined resulted in
structural invention such as the introduction of the windscreen, incorporation of wheels
into the body and the insetting of the headlamps into the front of the car. This was
probably the fastest developing time in automobiles history as the majority of the work
was to try and reduce the aerodynamic drag. This happened up to the early 1950‟s,
where by this time the aerodynamic dray had been cut by about 45% from the early cars
such as the Silver Ghost. However, after this the levels of drag found on cars began to
slowly increase. This was due to the way that the designing was thought about. Before
1950, designers were trying to make cars as streamlined as possible to make it easier for
the engine, yet they were restricting the layout of the interior for the car. After 1950, the
levels of aerodynamic drag went up because cars were becoming more family friendly
and so as a consequence the shapes available to choose were more limited and so it was
not possible to keep the low level of aerodynamic drag (Fig2.1). The rectangular shape
made cars more purposeful for the family and so it is fair to say that after 1950 the
designing of cars was to aid the lifestyle of larger families.

Fig.2.1-Evolution of shape of the cars.

(https://www.pakwheels.com/blog/history-drag-coefficients-cars/)

3
 Graph 2.1-Falctuation of fuel price from 1930 to 2010.
(https://www.youtube.com/watch?v=IVjmIovOPek)

Although this was a good thing for families, it didn‟t take long before the issue of
aerodynamics came back into the picture in the form of fuel economy. During the 1970‟s
there was a fuel crisis as shown in graph 2.1 and so the demand for more economical
cars became greater, which led to changes in car aerodynamics. During the 1970‟s there
was a fuel crisis and so the demand for more economical cars became greater, which led
to changes in car aerodynamics. If a car has poor aerodynamics then the engine has to do
more work to go the same distance as a car with better aerodynamics, so if the engine is
working harder it is going to need more fuel to allow the engine to do the work, and
therefore the car with the better aerodynamics uses less fuel than the other car. This
quickly led to a public demand for cars with a lower aerodynamic drag in order to be
more economical for the family.

4
This diagram 2.2 below shows the typical use of cars energy that it gets,

Fig 2.2-Use of car energy.

(https://www.utc.edu/college-engineering-computer-science/research/cete/hybrid.php)

Only about 15% of the energy from the fuel you put in your tank gets used to
move your car down the road or run useful accessories, such as air conditioning. The rest
of the energy is lost to engine and driveline inefficiencies and idling. Therefore, the
potential to improve fuel efficiency with advanced technologies is enormous.

Now a day‟s almost all cars are manufactured aerodynamically, one

misconception that everyone has is aerodynamics is all about going faster, in a way it is
true but it is not all about speed, by designing the car aerodynamically we can reduce the
friction that it encounters and there by power needed to overcome would be less thus
fuel can be saved; In the modern era where our fuel resources are fast depleting all the
efforts are to find alternate sources of energy or to save our current resources or
minimize the use of current resources like fuels, so now a day‟s aerodynamics are given
very much importance as everyone like to have a good looking , stylish and fuel efficient
car.

5
Chapter 3:

AERODYNAMIC FORCES ON A BODY

Fig 3.1-Aerodynamics forces on a body.

(https://www.researchgate.net/figure/Forces-acting-on-a-moving-vehicle-Himme-and-
OHanlon-nd_fig1_327237107)

3.1 LIFT
It is the sum of all fluid dynamic forces on a body normal to the direction of
external flow around the body. Lift is caused by Bernoulli’s effect which states that air
must flow over a long path in order to cover the same displacement in the same amount
of time. This creates a low pressure area over the long edge of object as a result a low
pressure region is formed over the aerofoil and a high pressure region is formed below
the aerofoil, it is this difference in pressure that creates the object to rise
F=(1/2)CLdV2A
Where :
CL= Coefficient of Lift, dependent on the specific geometry of the object, determined
experimentally,
d= Density of air,
V=Velocity of object relative to air,
A=Cross-sectional area of object, parallel to wind.

6
3.2 DRAG
It is the sum of all external forces in the direction of fluid flow, so it acts opposite
to the direction of the object. In other words drag can be explained as the force caused by
turbulent airflow around an object that opposes the forward motion of the object through
a gas or fluid.

F=(1/2)CDdV2A

where:
CD= Coefficient of Drag, dependent on the specific geometry of the object, determined
experimentally,
d= Density of air,
V=Velocity of object relative to air,
A= cross section of frontal area.
Since drag is dependent on square of velocity it is most predominant when object
is traveling at very high speeds. It is the most important aerodynamic force to study
because it limits both fuel economy of a vehicle and the maximum speed at which a
vehicle can travel.

3.2.1 DRAG COEFFICIANT

To calculate the aerodynamic drag force on an object, the following formula can
be used:

Where:
F - Aerodynamic
drag force
F=½ C - Coefficient of
CDAV² drag
D - Density of air
A - Frontal area
V - Velocity of object

In this system, D as air density is expressed in kg/m³. The frontal area is the
surface of the object viewed from a point that objects is going to. It's expressed in m³.
The better (lower) the number is the easier it is for air to pass around a car.

7
 Fig 3.2-Drag coefficient of some shapes.

(https://en.wikipedia.org/wiki/Drag_coefficient)

It is the measure of the aerodynamic efficiency of the car.

3.3 WEIGHT
It is actually just the weight of the object that is in motion .i.e. the mass of the
object multiplied by the magnitude of gravitational field. This weight has a significant
effect on the acceleration of the object.
3.4 THRUST
When a body is in motion a drag force is created which opposes the motion of
the object so thrust can be the force produce in opposite direction to drag that is higher
than that of drag so that the body can move through the fluid. Thrust is a reaction force
explained by Newton‟s second and third laws, The total force experienced by a system
accelerating in mass “m” is equal and opposite to mass “m” times the acceleration
experienced by that mass

8
Chapter 4:

STUDY OF AERODYNAMICS OF CARS

In order to improve the aerodynamics we must first know how the flow of air
past a car, if we visualize a car moving through the air. As we all know, it takes some
energy to move the car through the air, and this energy is used to overcome a force
called Drag.

4.1 DRAG

A simple definition of aerodynamics is the study of the flow of air around and
through a vehicle, primarily if it is in motion. To understand this flow, you can visualize
a car moving through the air. As we all know, it takes some energy to move the car
through the air, and this energy is used to overcome a force called Drag.

Drag, in vehicle aerodynamics, is comprised primarily of two forces. Frontal

pressure and rear vacuum.

4.2 DRAG FORCE AT LOW SPEEDS

The total drag force decreases, meaning that a car with a low drag force will be
able to accelerate and travel faster than one with a high drag force. This means a smaller
engine is required to drive such a car, which means less consumption of fuel.

4.3 CAR WEIGHT

As with the parts inside the engine, when the entire car is made lighter, through
the use of lighter materials or better designs, less force is required to move the car. This
is based on F=MA or more accurately, A=F/M, so as mass of the car decreases, the
acceleration increases, or less force is required to accelerate the lighter car.

9
4.4 FRONT END

Fig 4.1-Frontal pressure.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

Frontal pressure is caused by the air attempting to flow around the front of the car
(Fig.4.1). As millions of air molecules approach the front grill of the car, they begin to
compress, and in doing so raise the air pressure in front of the car. At the same time, the
air molecules traveling along the sides of the car are at atmospheric pressure, a lower
pressure compared to the molecules at the front of the car. The compressed molecules of
air naturally seek a way out of the high pressure zone in front of the car, and they find it
around the sides, top and bottom of the car. Improvements at the front can be made by
ensuring the „front end is made as a smooth, continuous curve originating from the line
of the front bumper‟. Making the screen more raked (i.e. not as upright) „tends to reduce
the pressure at the base of the screen to lower the drag‟. However, much of this
improvement arrives because a more sloped screen means a softer angle at the top where
it meets the roof, keeping flow attached. Similar results can be achieved through suitably
curved roofs.

10
Graph 4.1 clearly shows that drag force is directly proportional to frontal area.(results of
wind tunnel tests)

Graph 4.1-Froce vs Frontal area.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

4.5 REAR END

Rear vacuum (a non-technical term, but very descriptive) is caused by the "hole"
left in the air as the car passes through it as shown in fig.4.2. To visualize this, imagine a
bus driving down a road. The blocky shape of the bus punches a big hole in the air, with
the air rushing around the body, as mentioned above. At speeds above a crawl, the space
directly behind the bus is "empty" or like a vacuum. This empty area is a result of the air
molecules not being able to fill the hole as quickly as the bus can make it. The air
molecules attempt to fill in to this area, but the bus is always one step ahead, and as a
result, a continuous vacuum sucks in the opposite direction of the bus. This inability to
fill the hole left by the bus is technically called Flow detachment .At the rear of
vehicles, the ideal format is a long and gradual slope. As this is not practical, it has been
found that „raising and/or lengthening the boot generally reduce the drag”.

11
 In plan view, rounding corners and „all foreward facing elements‟ will reduce
drag. Increases in curvature of the entire vehicle in plan will usually decrease drag
provided that frontal area is not increased. „Tapering the rear in plan view‟, usually from
the rear wheel arch backwards, „can produce a significant reduction in drag‟. Under the
vehicle, a smooth surface is desirable as it can reduce both vehicle drag and surface
friction drag. „For a body in moderate proximity to the ground, the ideal shape would
have some curvature on the underside.‟

Fig 4.2-Rear vacuum.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

Flow detachment applies only to the "rear vacuum" portion of the drag equation,
and it is really about giving the air molecules time to follow the contours of a car's
bodywork, and to fill the hole left by the vehicle, The reason keeping flow attachment is
so important is that the force created by the vacuum far exceeds that created by frontal
pressure, and this can be attributed to the Turbulence created by the detachment as
Fig.4.3 shows.

12
 Fig 4.3-Turbulence.
(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

4.6 LIFT OR DOWNFORCE

One term very often heard in race car circles is Down force. Down force is the
same as the lift experienced by airplane wings, only it acts to press down, instead of
lifting up. Every object traveling through air creates either a lifting or down force
situation. Race cars, of course use things like inverted wings to force the car down onto
the track, increasing traction. The average street car however tends to create lift. This is
because the car body shape itself generates a low pressure area above itself.
For a given volume of air, the higher the speed the air molecules are traveling,
the lower the pressure becomes. Likewise, for a given volume of air, the lower the speed
of the air molecules, the higher the pressure becomes. This of course only applies to air
in motion across a still body, or to a vehicle in motion, moving through still air.
When we discussed Frontal Pressure, above that the air pressure was high as the
air rammed into the front grill of the car. What is really happening is that the air slows
down as it approaches the front of the car, and as a result more molecules are packed into
a smaller space. Once the air Stagnates at the point in front of the car, it seeks a lower

13
pressure area, such as the sides, top and bottom of the car.
Now, as the air flows over the hood of the car, it's loses pressure, but when it
reaches the windscreen, it again comes up against a barrier, and briefly reaches a higher
pressure. The lower pressure area above the hood of the car creates a small lifting force
that acts upon the area of the hood (Sort of like trying to suck the hood off the car). The
higher pressure area in front of the windscreen creates a small (or not so small) down
force. This is akin to pressing down on the windshield.
Where most road cars get into trouble is the fact that there is a large surface area
on top of the car's roof. As the higher pressure air in front of the wind screen travels over
the windscreen, it accelerates, causing the pressure to drop. This lower pressure literally
lifts on the car's roof as the air passes over it. Worse still, once the air makes its way to
the rear window, the notch created by the window dropping down to the trunk leaves a
vacuum or low pressure space that the air is not able to fill properly. The flow is said to
detach and the resulting lower pressure creates lift that then acts upon the surface area of
the trunk.

Fig 4.4-Drag, Lift and Downforce from over body flow.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)
Not to be forgotten, the underside of the car is also responsible for creating lift or
down force. If a car's front end is lower than the rear end, then the widening gap between

14
the underside and the road creates a vacuum or low pressure area, and therefore
"suction" that equates to down force. The lower front of the car effectively restricts the
air flow under the car. So, as you can see, the airflow over a car is filled with high and
low pressure areas, the sum of which indicates that the car body either naturally creates
lift or down force.

Fig 4.5-Downforce on raked underbody.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-
design/)

15
Chapter 5:
AERODYNAMIC DEVICES

5.1 WINGS & SPOILERS

What this wings or spoilers do is it prevents the separation of flow and there by
preventing the formation of vortices or helps to fill the vacuums in the rear end more
effectively thus reducing drag. So what actually this wing does is that, The wing works
by differentiating pressure on the top and bottom surface of the wing. As mentioned
previously, the higher the speed of a given volume of air, the lower the pressure of that
air, and vice-versa. What a wing does is make the air passing under it travel a larger
distance than the air passing over it (in race car applications). Because air molecules
approaching the leading edge of the wing are forced to separate, some going over the top
of the wing, and some going under the bottom, they are forced to travel differing
distances in order to "Meet up" again at the trailing edge of the wing. This is part of
Bernoulli's theory. What happens is that the lower pressure area under the wing allows
the higher pressure area above the wing to "push" down on the wing, and hence the car
it‟s mounted to.

The way a real, shaped wing works is essentially the same as an airplane wing,
but it's inverted. An airplane wing produces lift, a car wing produces negative lift or in
other words what we call us, downforce. That lift is generated by a difference in pressure
on both sides of the wing. .

But how is the difference in pressure generated? Well, if you look closely at the
drawings, you'll see that the upper side of the wing is relatively straight, but the bottom
side is curved. This means that the air that goes above the wing travels a relatively
straight path, which is short. The air under the wing has to follow the curve, and hence
travel a greater distance. Now there's Bernoulli's law, which basically states that the total
amount of energy in a volume of fluid has to remain constant. (Unless you heat it or
expose an enclosed volume of it to some form of mechanical work) If you assume the air
doesn't move up and down too much, it boils down to this: if air (or any fluid, for that
matter) speeds up, its pressure drops. From an energetic point of view, this makes sense:
If more energy is needed to maintain the speed of the particles, there's less energy left do

16
work by applying pressure to the surfaces.

In short: on the underside, air has to travel further in the same amount of time,
which means it has to speed up, which means its pressure drops. More pressure on top of
the wing and less on the underside results in a net downward force called downforce.

5.1.1 WINGS

Probably the most popular form of aerodynamic aid is the wing. Wings perform
very efficiently, generating lots of down force for a small penalty in drag. Spoilers are
not nearly as efficient, but because of their practicality and simplicity, spoilers are used a
lot on sedans.

The wing works by differentiating pressure on the top and bottom surface of the
wing. As mentioned previously, the higher the speed of a given volume of air, the lower
the pressure of that air, and vice-versa. What a wing does is make the air passing under it
travel a larger distance than the air passing over it (in race car applications). Because air
molecules approaching the leading edge of the wing are forced to separate, some going
over the top of the wing, and some going under the bottom, they are forced to travel
differing distances in order to "Meet up" again at the trailing edge of the wing. This is
part of Bernoulli's theory.

What happens is that the lower pressure area under the wing allows the higher
pressure area above the wing to "push" down on the wing, and hence the car it's mounted
to. See the diagram 5.1 below:

Fig 5.1-Wing.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

17
 Wings, by their design require that there be no obstruction between the bottom of
the wing and the road surface, for them to be most effective. So mounting a wing above
a trunk lid limits the effectiveness.

5.1.2 SPOILERS

Spoilers spoil the air flow that‟s why they are spoilers. They are used primarily
on sedan-type race cars. They act like barriers to air flow, in order to build up higher air
pressure in front of the spoiler. This is useful, because as mentioned previously, a sedan
car tends to become "Light" in the rear end as the low pressure area above the trunk lifts
the rear end of the car. See the diagram 5.2 below:

Fig 5.2-Spoiler.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

Front air dams are also a form of spoiler, only their purpose is to restrict the air
flow from going under the car.

18
5.2 SCOOPS

Fig 5.3-Scoop in a F1 car.

Scoops, or positive pressure intakes, are useful when high volume air flow is
desirable and almost every type of race car makes use of these devices. They work on
the principle that the air flow compresses inside an "air box", when subjected to a
constant flow of air. The air box has an opening that permits an adequate volume of air
to enter, and the expanding air box itself slows the air flow to increase the pressure
inside the box. See the diagram 5.4 below:

Fig 5.4-Scoop/positive pressure intake.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

19
5.3 NACA DUCTS

NACA stands for "National Advisory Committee for Aeronautics". NACA is one
of the predecessors of NASA. In the early days of aircraft design, NACA would
mathematically define airfoils (example: NACA 071).

Fig 5.5-NACA ducts in a racing car.

The purpose of a NACA duct is to increase the flow rate of air through it while
not disturbing the boundary layer. When the cross-sectional flow area of the duct is
increased, you decrease the static pressure and make the duct into a vacuum cleaner, but
without the drag effects of a plain scoop. The reason why the duct is narrow, then
suddenly widens in a graceful arc is to increase the cross-sectional area slowly so that
airflow does separate and cause turbulence (and drag).

NACA ducts are useful when air needs to be drawn into an area which isn't
exposed to the direct air flow the scoop has access to. Quite often you will see NACA
ducts along the sides of a car. The NACA duct takes advantage of the Boundary layer
(Fig5.6), a layer of slow moving air that "clings" to the bodywork of the car, especially
where the bodywork flattens, or does not accelerate or decelerate the air flow. Areas like
the roof and side body panels are good examples. The longer the roof or body panels, the
thicker the layer becomes (a source of drag that grows as the layer thickens too).
Anyway, the NACA duct scavenges this slower moving area by means of a specially
shaped intake. The intake shape, shown below, drops in toward the inside of the
bodywork, and this draw the slow moving air into the opening at the end of the NACA
duct. Vortices are also generated by the "walls" of the duct shape, aiding in the
Scavenging. The shape and depth change of the duct are critical for proper operation.

20
 Fig 5.6-NACA Duct.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-
design/)

5.4 SPLITTER

A lot of rear downforce itself can cause under steer, to balance is to add
downforce to the front tires using a splitter, see fig5.7.

Fig5.7-Splitter.

(https://allfitautomotive.com/blog/what-is-a-car-lip-splitter-and-what-does-it-do-allfit-
automotive/)

21
 Air stacks up against the car‟s front end and creates a high pressure area before
moving either over or under the body. When more air goes into that tight space under the
car than the amount of air that goes over it, there is lift off. Most production in street cars
generate positive lift at high speed and like the wing it really rather have lower pressure
air go under the car whilst high pressure air goes over the top. When splitter is added, it
increase the amount of area, air can stack up against while helping more of it move over
the car. Now the more pressure on the top and lower pressure underneath so net
downforce on those front tires.

5.5 AIR DAM AND CANARDS

Air dam usually has a couple of jobs, it directs more air over the top of the car
than underneath to reduce lift while also diverting air to the radiator, intake, inter cooler
or oil cooler to keep car from overheating.

Fig5.8-Front air dam.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

Air dam also cut down an overall drag even on a boxy vehicle without it the air
would be tripped up by all the blocky shapes that usually find behind hiding that smooth
bodywork on the front as shown in fig.5.8.

On the corners of race cars air dam there might be canards (Fig.5.9) also called
dive plates. Canards are usually flat, wedge shaped and angled upward toward the back
of the car, they direct the air that moves around the side of the air dam upwards which

22
creates a little it of dowforce, it‟s to that much because they are so small but it‟s enough
to help fine tune the balance between downforce on the front tires and the rear tires.
Canards can also used to deflect air around the front tires because they can be source of
drag or they can be used to direct more air up into the wings past at the back

Fig.5.9-Canards.

(https://indtuning.com/product/indtuning-bmw-m4-front-canards-cf/)

5.6 UNDERTRAY AND DIFFUSER

Underneath the car there‟s a whole lot of nooks and crannies and junk like brake
lines and exhaust pipes they are all meshing up the air flow, adding a smooth under tray
to cover as shown in fig.5.10, all that stuff goes a long way to reducing turbulence and
drag. It lets the air move below the car and much more quickly and that reduces the air
pressure and can enhance the downforce

Fig.5.10-Car underbody aerodynamics.

(http://www.rapid-racer.com/aerodynamic-upgrades.php)

23
 Diffuser is typically a rear under tray shape to make a gradually bigger space at
the back of the car (Fig.5.11) but some race cars have front diffusers too. It activates
what‟s called a venture effect which is when a fluid speeds up as it flows through a
more constricted area like the space under car and Bernoulli‟s principal that says a fast
moving fluid has lower pressure that means even more downforce, as the space at back
of the car gradually increase in size than because of diffuser all the fast moving low
pressure air from underneath the car rushes up to fill that space this helps draw even
more air across the underside of the car.

Fig.5.11 Diffuser.

(https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/)

When it gets to the expansion area it slows down and gains pressure with high
pressure surrounding the car on all sides and a lot less pressure underneath and overall
vacuum effects occurs and it sucks the car down to the road. Now that slowed air can
smoothly join back up with slower higher pressure air flowing all around the car. This
gentle reunion reduces drag at the fact which results in even more downforce keeping the
air flowing effortlessly without turbulence as what males all of this works so well so
vertical dividers called strikes are placed in the diffuser to help keep the air orderly, see
fig.5.12 below.

24
 Fig.5.12-Diffuser.

(http://www.rapid-racer.com/aerodynamic-upgrades.php)

Downforce from splitter and wings usually comes at the expense of a lot more
drag but adding a smooth under tray and a well designed diffuser can reduce drag so
together they are one of the most important ways to increase downforce.

5.7 SIDE SKIRTS

There is an area of higher pressure all around the top and an area of really low
pressure underneath, now all that higher pressure want to rush into the low pressure are
and that is exactly increase lift and that is what side skirts are for. The ideal side skirts
extend as close to the ground as possible to block that higher pressure air from sneaking
back under the car and around the sides that would increase lift and ruin the downforce.

Fig.5.13-Side skirts.

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5.8 VORTEX GENERATORS

Pushing a car through air causes some friction because it‟s got drag. Some air
molecule stuck near the surface and that‟s called boundary layer meanwhile the faster
air tries to follow the curved shape of roof and rear window and that‟s called attached
flow.

It would be perfect if the air smoothly and non dragly followed the window down
then float across the rear wing where it would generate downforce just like it‟s supposed
to but it does not happens. Instead the attached flow peels off eight around the end of the
roofline and becomes a separated flow, dispensing off into the atmosphere where it
cannot be used, that‟s why rain drop don‟t always flow off back window there‟s just a
swirling massive turbulence and that‟s not going to make any downforce when its gets to
the wing. However if vortex generator are placed in the stagnant area around the trailing
edge of the roof where the air starts to separate they generate vortices off their tips
(Fig.5.14) and that helps draw the fast moving air down into the boundary layer which
keeps the air flow attached for longer so vortex generator are to make sure that air passes
over the rear wing and generates downforce.

Fig.5.14-Vortex generators aerodynamics.

(https://www.pinterest.com/pin/749145719241942506/)

26
 Chapter 6:

METHODS FOR EVALUATING AERODYNAMCIS OF CARS

6.1 WIND TUNNELS

A wind tunnel is a research tool developed to assist with studying the effects of
air moving over or around solid objects. Air is blown or sucked through a duct equipped
with a viewing port and instrumentation where models or geometrical shapes are
mounted for study. Various techniques are then used to study the actual airflow around
the geometry and compare it with theoretical results, which must also take into account
the Reynolds number and Mach number for the regime of operation. Threads can be
attached to the surface of study objects to detect flow direction and relative speed of air
flow.

Dye or smoke can be injected upstream into the airstream and the streamlines that
dye particles follow photographed as the experiment proceeds.

Traditionally, wind tunnel testing was a sizeable trial and error process, ongoing
throughout the development of a vehicle. Today, with the high level of CAD prediction
and pre-production evaluation, coupled with a greater human understanding of
aerodynamics, wind tunnel testing often comes into the design process later. The wind
tunnel is the proving ground for the vehicle's form and allows engineers to obtain
considerable amounts of advanced information within a controlled environment.

Fig 6.1-Wind tunnel.

27
 Now days the aerodynamic studies are not constrained to the flow of air past cars
but also a number of other factors like new methods are developed to provide a greater
level of detailed information. Special pressure sensitive paint is now used in the wind
tunnel to graphically show levels of air pressure on a vehicle how it is done is that ,Two
different images are obtained, one at normal room air pressure (wind-off) and a second
in which the wind tunnel is running (wind-on) at a desired test speed. These differences
in color, from wind-off to wind-on, are used to calculate surface pressure.

A bank of blue lights illuminates the car to be tested that has pressure-sensitive
paint applied on the driver's side window. The car and lights are in a wind tunnel at Ford
Motor Company's Dearborn Proving Ground. Ford researchers have developed a
computerized, pressure-sensitive paint technique that measures airflow over cars,
shaving weeks off current testing methods. A digital camera near the blue lights captures
this information and feeds it into a computer, which displays the varying pressure as
dramatically different colors on a monitor.

The images obtained from tests in the wind tunnel are captured on computer.
They can then be used to study air flow patterns across a vehicle, highlighting areas of
possible refinement or improvement. Additionally, actual data from a production ready
model can be compared with pre-production computer predictions which can in turn help
improve the accuracy of the early design stages.

6.2 SOFTWARES FOR EVALUTING AERODYNAMICS OFCARS

Now days a large number of software‟s are developed for the analysis and
optimization of aerodynamics in automobiles. Earlier times the cars were worked
directly on wind tunnels where they prepared different shapes or cross sections and
tested upon the cars, during those times it was not possible to test the for small areas that
is for a small part of front area etc there testing were made for the entire cross sections,
But with the introduction of computational fluid dynamics i.e. the use of computers to
analyze fluid flows where the entire area is divided in to grids and each grid is analyzed
and suitable algorithms are developed to solve the equations of motion based on CFD
large number of software‟s are developed for the design and analyzing aerodynamics the
most commonly used software‟s are ANSYS,CATIA.

28
 Fig.6.2-Hennessey Venom GT aerodynamics at 30 km/s.
(https://www.google.com/url?sa=i&url=https%3A%2F%2Ftwitter.com%2Fgarcfd%2Fst
atus%2F816317514703663105&psig=AOvVaw23CUXpJfPNXfey3LCUQLOl&ust=15
89437611068000&source=images&cd=vfe&ved=0CA0QjhxqFwoTCNCPsOaasOkCFQ
AAAAAdAAAAABAJ )

Here are some of the features of commonly used software Alias surface studio

6.2.1 ALIAS SURFACE AND AUTO STUDIO

Alias Surface Studio is a technical surfacing product designed for the

development surfaces. It offers advanced modeling and reverse engineering tools, real-
time diagnostics and scan data processing technology. Surface Studio is comprised of a
complete suite of tools for creating surface models to meet the high levels of quality,
accuracy and precision required in automotive styling.

29
This software performs all the basics of design right from the sketching to evaluation.
Features:
1) User Interaction
A user interface that enables creativity and efficiency.
2)Sketching
A complete set of tools for 2D design work tightly integrated into a 3D modeling
environment.
3)2D/3DIntegration
Take advantage of your sketching skills throughout the design process. Add details
and explore ideas quickly by sketching over 3D forms before taking the time to model
them.
4)Modeling
Industry-leading, NURBS-based surface modeler.
5)Advanced Automotive Surfacing Tools
Surface creation tools that maintain positional, tangent or curvature continuity
between surfaces - for high quality, manufacturability results.
6) Reverse Engineering
Tools for importing and configuring cloud data sets from scanners for visualizing,
as well as extracting feature lines and building surfaces based on cloud data.
7)EvaluationTools
Tools to analyze and evaluate the styling and physical properties of curves and
surfaces interactively, while creating and editing geometry.
8)Rendering
Create photorealistic images using textures, colors, highlights, shadows,
reflections and backgrounds.
9)Animation
Animations can be used for high quality design presentations, design analysis of
mechanisms, motion and ergonomic studies, manufacturing or assembly simulation.
10) Data Integration
Support for industry-standard data formats and a wide range of peripheral
devices. These software‟s are now commonly in use as wind tunnel testing is an
expensive process as compared to this software‟s where we get more accurate and easily
the test results.

30
 Chapter 7:

AERODYNAMIC DESIGN TIPS

Now almost all cars are tested for getting the optimum aerodynamic configuration, these
are some aerodynamics design tips:-
 Keep the vehicle low to the ground, with a low nose, and pay attention to the angle of
wind shield.
 Cover the wheel wells, Open wheels create a great deal of drag and air flow turbulence
 Enclose the under carriage (avoid open areas-convertibles, etc.)
 Make corners round instead of sharp.
 The underbody should be as smooth and continuous as possible, and should sweep out
slightly at rear.
 There should be no sharp angles (except where it is necessary to avoid crosswind
instability).
 The front end should start at a low stagnation line, and curve up in a continuous line.
 The front screen should be raked as much as is practical.
 All body panels should have a minimal gap.
 Glazing should be flush with the surface as much as possible.
 All details such as door handles should be smoothly integrated within the contours.
 Minor items such as wheel trims and wing mirrors should be optimized using wind
tunnel testing.
 Using spoilers or wings.

7.1 AERODYNAMICS DESIGN TIPS FOR A VEHICLE YOU

ALREADY OWN
 Keep your vehicle washed and waxed. This reduces skin friction.
 Remove mud flaps from behind the wheels.
 Add a spoiler to the front fender or the rear of the car. Having it on the front fender
reduces air flow beneath the car, while having it behind will decrease the low pressure
behind the car and reduce drag.
 Close your windows, put your top up, and close your sun roof. All at once!
 Avoid having roof-racks and carriers on your car.
 For pickups: cover the back, take the gate off, or at least leave the gate open. Air gets
trapped in the bed and causes major drag.
 Place your license plate out of the air flow.

31
 CONCLUSION

Earlier cars were poorly designed with heavy engines, protruding parts and
rectangular Shapes due to which they consumed large quantities of fuel and became
unaffordable. all theses factors lead to the development and need of aerodynamics in the
design of cars now it would be fair to say that almost all cars are tested for getting the
optimum aerodynamic configuration.

32
 REFERENCES

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automobile-aerodynamics/ (accessed on 01/05/2020)
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 https://www.pakwheels.com/blog/history-drag-coefficients-cars/ (accessed on
01/05/2020)
 Edger J. 2019. (Modifying the Aerodynamics of Your Road Car). YouTube
playlist: https://www.youtube.com/playlist?list=PL52-wxMBN-
Egg8v8X6ixIacFtq3Cw5fDz (accessed on 02/05/2020)
 https://en.wikipedia.org/wiki/Drag_coefficient (accessed on 02/05/202)
 https://www.researchgate.net/figure/Forces-acting-on-a-moving-vehicle-
Himme-and-OHanlon-nd_fig1_327237107 (accessed on 02/05/2020)
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03/05/2020)
 https://allfitautomotive.com/blog/what-is-a-car-lip-splitter-and-what-does-it-do-
allfit-automotive/ (accessed on 03/05/2020)
 https://en.wikipedia.org/wiki/Automotive_aerodynamics (accessed on
04/05/2020)
 www.cardesignonline.com (accessed on 05/05/202)
 https://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-
design/ (accessed on 05/05/2020)
 https://carbiketech.com/air-dam-front-splitter/ (accessed on 06/05/2020)
 http://www.rapid-racer.com/aerodynamic-upgrades.php (accessed on
07/05/2020)
 https://www.caranddriver.com/news/a15362503/how-a-wind-tunnel-works/
(accessed on 07/05/2020)
 https://en.wikipedia.org/wiki/Class_A_surface (accessed on 07/05/2020)

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