Internship ReportOn

Conceptual Aerodynamic

Frontal Design of a Vehicle

(May-June 2013)

AMITY SCHOOL OF ENGINEERING & TECHNOLOGY

Submitted by: Submitted to:

Akshay Mistri Mr. Sonu Sharma

Abhishek Thakur (Faculty Guide)

Sarthak Anand

Tushar Rastogi

Prog. /Section: B.Tech 5MAE3 (2011-15)

ACKNOWLEDGEMENT

The special thanks goes to Mr.Sonu Sharma. The supervision and support that he gave truly

helped the progression and smoothness of the internship program. The co-operation

is highly appreciated.

Topics studied during the project were highly educative and interesting. This internship

program has made us realize the value of working together as a team and gave us a new

experience of working in aerodynamics field.

This training program gave us opportunity to work in different fields and exposed us to topics

of great interest.

We are also thankful to all the aerodynamics faculties who supported us to complete this

project successfully.

Last but not the least, we would also like to thank lab assistant faculties for their kind

support. It would have been very difficult for us to complete the experiment on our models

without their assistance.

ABSTRACT

The objective of this project is to modify the frontal design of existing vehicles

aerodynamically. Every vehicle in motion has some air drag associated with it. Hence it is

required to streamline the shape of the vehicles to produce minimum air drag which in return

can increase the efficiency of vehicles.

The above objective of modifying the shape of vehicles for a better aerodynamic shape was

accomplished by making few models with different front shape which can be practically

manufactured with least amount of changes in the present situation. All the models were

tested for drag force under similar conditions for comparison.

After the test a model with least drag force is chosen as the final model which is the final

result of our prime objective.

The final model so obtained is far better aerodynamic than present shapes of currently

running transportation buses and trucks. Also the model obtained is technically feasible to

manufacture with current technology.

Thus the better aerodynamic shape will ensure less amount of drag force and will increase the

efficiency of existing vehicles.

Contents

Title Page

1.Introduction 01

2.Material 02-052.1 Adjusting vehicle shape to reduce drag

03

3.Methodology 05-073.1. Drag force equation 063.2 Dimensions 073.3 Force on a real bus 07

4.Results 07-124.1 Drag force table 084.2 Newton’s Sine Square law 094.3 Coefficient of Drag 104.4 Drag force on actual bus 114.5 Increase in fuel efficiency 11-12

5.Conclusion 12

6.References 13

1. Introduction

Aerodynamics deals with all the processes that can be observed in flows around or through a

body. The drag co-efficient Cw is determined in a wind tunnel. The lower the Cw value the

higher the final speed results in lower fuel consumption. In the light of increasing fuel prices,

it has become important for all commercial vehicle manufacturers to have favorable

aerodynamic design to improve the Cw value. The recent trend is to have fully paneled

commercial vehicles. Aerodynamics is used in many fields. It is also used in road cars and

mainly it is applied in designing an Aeroplane. The frictional force of aerodynamic drag

increases significantly with vehicle speed. This concept of increasing and decreasing drag

force has a great effect on the speed of vehicle. The front design of the vehicle is always

taken into consideration, it is mainly the frontal design of the racing cars which makes it run

faster as the air is not restricted but it is allowed to flow smoothly. As in Automobile shape

plays an important role in reducing drag at higher speed. The frontal design model of the

vehicle is made at different angles and it is tested in the wind tunnel so as to get the reduced

drag. The shape of a car, as the aerodynamic suggests, is largely responsible for how much

drag the car has. Ideally, the car body should have a small grill, to minimize frontal pressure,

minimal ground clearance below the grill, to minimize air flow under the car. It should also

have a converging "Tail" to keep the air flow attached. Apart from Rolling resistance, the

Aerodynamic Drag also represent the largest proportion of the overall resistance. It increases

in the same way as that of rolling resistance on movement of the vehicle and arises with

increase in driving speed.

2. Materials

This project “conceptual Aerodynamics of frontal design of the vehicle” is mainly

associated in finding the drag force when the vehicle moves with great speed. To find the

drag force four models were made, inclined at different angles so as to reduce the drag

force, 60 degree, 90 degree, 120degree, 180 degree where tested on the wind tunnel with

the help of the apparatus “3 component balance”. The models were made of hard

cardboard, it was assembled strongly so that it can resist the force of the air in the wind

tunnel. The cardboard made was varnished and was made smooth and it was painted so as

to avoid errors while finding the drag.

Fig.1 A Test Model [90 deg.] mounted in Wind Tunnel

In order to optimise the vehicle design with regard to aerodynamic the front section of the

driver’s cabin is rounded off in conjunction with the air deflection elements and the use of

front apron. An aerodynamically designed drivers cabin alone, however leads to

reinforced air flow to the non optimised superstructure. The total Cw value then reached

is even higher than that of the commercial vehicles with a squared drivers cab and non

optimised superstructure. The reason for this is that with squared drivers cab the front

section of the superstructure is located in a separation zone and hence exposed to lower

aerodynamic drag. Fully panelled commercial vehicles achieve best consumption values

and hence increase the benefit to the fleet operators. In order to significantly reduce the

aerodynamic drag of the commercial vehicle with superstructure, a roof spoiler on the

drivers cab with side flaps and roof attachment is incorporated

2.1 Adjusting vehicle shape to reduce drag

The process of reducing the drag coefficient of a vehicle by altering the vehicle shape is

called streamlining. It was determined during the middle of the 20th century that the most

streamlined shape is a teardrop

Fig.2 Teardrop-shaped profiles are very aerodynamic and yield little drag

Although this design was emulated in various streamlined concept car models, the shape was

found to be impractical when designing an actual car, mainly due to the long and narrow end.

In case of buses teardrop shape is not given due to its large and heavy size. However, the air

that flows around the car swirls around the rear much more for the actual vehicle profile as

compared with the teardrop profile. These swirls are called vortices, and they represent a low-

pressure area behind the car. The low pressure behind the car creates a suction effect that tries

to pull the vehicle backwards. Therefore, reducing the size of the separation zone, which is

the area behind the car containing the vortices behind the car, is one of the predominant

methods of decreasing aerodynamic drag. This can be done by slightly tapering the rear end

of a car to reduce the size of the separation zone. As counterintuitive as it may seem, the rear

section of the car is the cause of the most drag on a vehicle. This is the same reason why the

example of holding a traffic cone outside of a car window has less drag when pointed away

from the direction a vehicle is moving.

There is a difference in the aerodynamics on the bus and truck. However the physics are

essentially the same. However, the aerodynamics of the bus is considerably better than those

of the truck. There are two reasons for this. On the one hand, the bus is an enclosed body and

its aerodynamic development is the responsibility of the manufacturer. On the other hand, the

focus with transportation of persons is not so much on maximum interior volume, rather on

maximum comfort. We can therefore optimise the bus aerodynamically from the front to the

rear. With the truck on the other hand, there is a towing vehicle and a separate semitrailer or

body designed by an independent body manufacturer who places utmost importance on

maximum load capacity within legal limits. We, as a towing vehicle manufacturer, also

devote attention to the needs of the driver and attempt to design the cab to be as spacious as

possible. This causes it be relatively square, which is not aerodynamically optimal. With the

bus we have more design freedom and can realise aerodynamic shapes easier, that means

design the front to be rounder. Taperings at the rear are also possible. The smaller the Cw

(drag coefficient) value, the more streamlined is the vehicle. Through good aerodynamics we

can save up to 2.0 litres fuel per 100 kilometres for coaches, depending on how good the

initial state is. The following graph depicts the amount of fuel used for upcoming different

types of forces.

Fig.3 Fuel Consumption in Various Situations

3.Methodology

We constructed four scaled down models of a standard size urban bus whose specifications

were taken from Urban Bus specifications- II, Ministry of Urban Development, Government

of India. The only difference in the scaled down models were the front faces as can be seen

from the pictures below.

Fig.4 Models with 60, 90, 120, 180 degree face respectively

It must be noted that the overall length, width, height and as a result the frontal area of all the

models is kept same. This kind of similarities makes the models comparable.

All the models were tested for aerodynamic drag force in wind tunnel with identical fluid

(air) velocity of about 26 m/sec [93.6 km/hr]. The mounting in the wind tunnel had an

electronic setup to which a “3 Component Balance” was connected.

This 3 Component Balance gives us values of lift, drag and pitching moment in Kg-f in two

modes i.e. Wind off and Wind on modes. Actual values of drag, lift and pitching moment can

be obtained by subtracting Wind off mode values from Wind on mode values. But as our

prime concern was drag force, we kept a check only on that.

The Drag force coefficient can be found out from the equation,

F=12

DV 2CD A .… Eq-1 [1]

where F is Drag Force

D is Fluid Density

V is Fluid Velocity

CD is Drag Coefficient

A is Frontal Area

3.1 Dimensions

Standard bus specifications: - Scaled down model specifications: -

Overall Length 12 metre

Overall Width 2.6 metre

Overall Height 3.8 metre

Scaling ratio for scaled down model: - [28:1]

3.2 Force on a real bus

Since the dimensions of model are scaled down by a factor of 28, area will be scaled by a

factor of (28)2. …. {Since area= (dimension) 2}

Overall Length 20 cm

Overall Width 9.3 cm

Overall Height 13.5 cm

From equation F=12

DV 2CD A ,

we can say that F (drag) is directly proportional to A (frontal area)

So, Drag force on a real bus FR will also scaled up by a factor of (28)2.

Therefore,

FR = (28)2 F ….Eq-2

4.Results

Several values of drag force were taken to reduce error and hence to obtain a more precise

result. These values are obtained by considering 5 second intervals and noting them from the

display of 3 component balance. With several values an average drag force can be found.

Multiplying the drag force by acceleration due to gravity “g” gives the drag force in Newton

which is the S.I unit of force.

The values of drag force are as follows -:

4.1 Table-1

S.No Model

(According to degree of face)

Drag Force (Kg-f)

(5 sec interval of run)

Drag Force

(Average)

(Kg-f)

Drag Force

(Newton)

1 60 0.268 0.384 3.767

0.419

0.424

0.426

2 90 0.504 0.498 4.885

0.493

0.502

0.495

3 120 0.608 0.616 6.042

0.620

0.625

0.614

4 180 0.750 0.757 7.426

0.760

0.755

0.765

It’s essential to take several values of drag force to obtain an accurate value. Several values

which were taken with interval of 5 seconds are depicted below in a graph. The bottom most

profile is of model with 60 deg. face angle. Red profile represents model with 90 deg. face

angle then green profile represents model with 120 deg. face angle with a purple profile

representing model with 180 deg. face angle on top.

5 10 15 200.2

0.3

0.4

0.5

0.6

0.7

0.8

0.268

0.419 0.424 0.426

0.504 0.493 0.502 0.495

0.608 0.62 0.625 0.614

0.75 0.76 0.755 0.765

60 Degree90 Degree120 Degree180 Degree

Graph 1

Drag Force (Kg-f) v/s Time of run

4.2 Newton’s Sine Square Law

It can be seen from table-1 that drag force increases as angle at the face increases. This can

also said theoretically using Newton’s Sine Square law which states that hydrodynamic force

Drag Force (Kg-f)

Time of run (seconds)

on surface is directly proportional to angle Q, where angle Q (theta) is shown in the picture

given below.

Fig.5

Rectilinear stream of discrete particles in our case is flow of air and body shown is the front

face of the bus. Comparison of drag force for the four models is shown below.

60 Degree 90 Degree 120 Degree 180 Degree0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.384

0.498

0.616

0.757

Drag Force for different Models

Graph 2

Fig.6 Drag Force (Kg-f) v/s Models

Drag Force (Kg-f)

Different Models

4.3 Coefficient of Drag

Drag coefficient can be found using the equation,

F= 0.5[D][V2][CD][A]

Where F (drag force) = 3.769 N (60 deg.) D (fluid density) =1.225Kg/m3

= 4.89 N (90 deg.) V (fluid velocity) = 26 m/sec

= 6.05 N (120 deg.)

= 7.431 N (180 deg.)

A (frontal area) = 0.135 X 0.0928 m2

= 0.012528 m2

Substituting the values mentioned above in the equation, drag coefficient can be found easily.

Model (According to Face angle) Drag Coefficient

60 deg. 0.72

90 deg. 0.94

120 deg. 1.17

180 deg. 1.43

4.4 Drag force on an actual bus

Drag force on a real bus can be calculated using equation,

FR = (28)2 (F) where FR is real drag force

F is model drag force

Model (according to face angle) Force (Newton)

60 deg. 2954.89

90 deg. 3833.76

120 deg. 4743.20

180 deg. 5825.90

4.5 Increase in fuel efficiency

We know that least amount of drag is experienced is model with 60 deg. face angle. So, we

will compare that model with 180 deg face model which represents the current condition of

buses and trucks.

Increase in fuel efficiency is derived by comparing the energy contents of drag force and the

fuel used to overcome that drag force. Generally the fuel used in buses and trucks is diesel, so

we will assume our fuel as diesel only and speed 26 m/sec.

4.5.1 Reduction in drag force when 60 deg face model is used in place of 180 deg

face model = 5825.90 – 2954.89 N

= 2871.01 N

4.5.2 Amount of energy associated with this reduction in drag force

= (Reduction in drag force) X (Distance moved by bus per second)

= (2871.01 N) X (26 m/sec)

= 74646.26 Joules

4.5.3 Latent heat of diesel[2] = 34.92 Mega Joule/ litre

4.5.4 Amount of diesel which can be saved if 60 deg face model is used

= (Amount of energy associated) / (Latent heat of diesel)

= (74646.26 Joule) / (34.92 X 106 Joule/litre)

= 2.14 X 10-3 Litre/second

= 7.6 Litre/hour

4.5.5 Amount of fuel saved per km = (Diesel saved) / (Speed)

= (7.6 litre/hour) / (93.6 km/hour)

= 0.0899 litre/km

= 0.09 litre/km

Therefore 0.09 litres of fuel can be saved every kilometre the vehicle moves if we use a 60

deg faced model for real buses and trucks.

5. Conclusion

Thus, it can be finally concluded that we can save 0.09 litres of diesel if we manufacture a 60

degree faced bus or truck every km it moves with an average speed of 26 m/sec [93.6 km/hr].

A 60 degree faced automobile is quite feasible to manufacture with existing technology.

6. References

6.1 Anderson John D Jr, Fundamentals of Aerodynamics, Volume 3, McGraw Hill,

New York, 2001 : 6-9

6.2 Hypertextbook.com

<http://hypertextbook.com/facts/2006/TatyanaNektalova.shtml> : 12