The aerodynamic shape of the Automobile
Meaning of Aerodynamics- When objects move through
air, forces are generated by the relative motion between air and surfaces of
the body, study of these forces generated by the motion of air is called-
aerodynamics.
The necessity of Aerodynamic Shape of Body:
- As the the demand for efficient and comfortable cars is increasing, the branch of automobile aerodynamics is playing an important role in improving overall performance of the vehicle.
- Due to air resistance, a forward motion of the car gets affected badly and hence it results in higher fuel consumption and lower speed of the vehicle.
- Hence it is the design engineer’s task to make the drag coefficient of the vehicle as small as possible by shaping the body aerodynamically.
Basic terms related to Car Aerodynamics
Lift- The summation of all fluid dynamic forces acting on
a body normal to the direction of external flow around the body. It works on
the principle of Bernoulli’s effect and results in raising the car body by
creating a pressure difference.
Drag- The summation of external forces in the direction
of fluid flow, so it acts opposite to the direction of the object. This force opposes
the forward motion of the body through a fluid.
For calculating drag force following formula is used:
F = ½ C.D.A.V2
Where F = Aerodynamic drag force
C = Coefficient of drag
D =
Density of air
A = Frontal
area
V =
Velocity of object
Thrust- It is the force acting in the opposite direction to
drag force so as to oppose it. To move the body through fluid, this thrust force
should be greater than the drag force.
Coefficient
of drag: It is the ratio of the drag on a body moving
through air to the product of the velocity and the surface area of the
body.
SR.NO
|
SHAPE
|
DRAWING
|
Coefficient
of drag
|
1
|
Sphere
|
 |
0.47
|
2
|
Half
sphere
|
0.42
|
|
3
|
Cone
|
0.5
|
|
4
|
Cube
|
1.05
|
|
5
|
Angled
Cube
|
0.80
|
|
6
|
Long
Cylinder
|
0.82
|
|
7
|
Short
Cylinder
|
1.15
|
|
8
|
Streamlined
Body
|
0.04
|
|
9
|
Streamlined
Half Body
|
0.09
|
Significance of Aerodynamic The shape of Automobile-
In previous days, not so much importance was given to
the aerodynamic shape. Hence as fig below shows, we can see the shape of the old
vehicle on which the negative effect of drag force was more.
 |
Fig. The old car with no aerodynamics |
As cars have become faster over the years, their
aerodynamic efficiency has become more crucial because of the amount of power
needed to propel a car at high speed rises with the cube of the speed. The
faster you are going, the more power it takes to go even faster.
 |
Fig. The car with an aerodynamically designed shape |
i) Air
drag is reduced due to aerodynamic shape.
ii) The aerodynamic
shape makes the driver comfortable by reducing the driver's effort to drive the vehicle.
iii) The speed
of the vehicle gets improved due to aerodynamic shape.
iv) As it
helps vehicles for less fuel consumption, better fuel economy is observed.
v) An aerodynamically
designed car gives better shapes and hence the aesthetic look of the vehicle
improves.
vi) The running
cost of the vehicle reduces.
vii) Aerodynamics
contributes to the environment by reducing noise pollution.
