Bridge engineering and aerodynamicsFull description
aerodynamics for gateFull description
Aerodynamics, Aeronautics, And Flight Mechanics - Barnes Warnock McCormick
Vehicle Aerodynamics
This book helps a lot for those who are intrested in AerodynamicsFull description
CFD on urban environment. Aerodynamics. Aerospace, Urban Planning
In this manual We have given the experimental procedure based on Anna university syllabus for all the experiments.Full description
Aero dynamics i university question with answer keyFull description
Solving the 2D case of tapered wingsDescription complète
Fundamentals of AerodynamicsFull description
Aerodynamics Solutions ManualFull description
Descripción: Basic Helicopter Aerodynamics
Marko Rodin - AerodynamicsFull description
Fundamentals of Aerodynamics
Aerodynamics Solutions Manual
AERODYNAMICS
An automobile is a small object submerged amid vast surrounding of air.
The motion of the vehicle takes place through a large mass of either stationary air, or air in motion.
The air exerts force on the auto vehicle.
It is the superstructure (body) ( body) of the vehicle which is mainly exposed to the air.
An arbitrary shaped body will experience a large air resistance which implies that there is more loss of engines power.
Consequently less power will be available to propel the automobile thereby causing less load carrying capacity and slow speed for the same fuel consumption.
Thus, there exists a need to profile aerodynamically suitable body.
The force exerted by air on a moving auto vehicle had two components, one in the direction of motion and the other in a direction perpendicular to the motion.
The force in the direction of motion is called drag F D and that in the perpendicular direction is known as lift F t, Fig.
The body profile of an automobile should be such that the lift force F L is zero or negligible, and then the total force on the body is drag force F D.
The viscosity of air is mainly responsible for drag on the body.
The arbitrary shaped body of an automobile, held stationary in a stream of air moving at a uniform velocity V, experiences shear force along its tangentia1 direction and pressure force in the normal direction Fig.
The shear forces are called frictional drag force F Df and the pressure forces are known as pressure drag force F Dp
Total drag on the body is therefore the sum of friction and pressure drags .
Thus
The magnitudes of friction drag and pressure drag depend on shape of the body. For example, a flat plate portion, Fig. (a) experiences only friction drag (.: F Dp = 0).
While the flat portion perpendicular to the direction of flow, Fig. (b) , feels only pressure drag due to pressure difference on the upstream and downstream sides of the body.
In this case F Df 0.
There can be several body profiles in between the two extreme cases described above.
For those cases the drag and lift may be calculated from
Where C D is coefficient of drag and C L is coefficient of lift, A is characteristic area of
=
the body which is the largest projected area of body on a plane perpendicular to the direction of flow of the air.
Wake : Quite often we see on the downstream side of a fast moving vehicle that the
small and light objects such as papers, pebbles etc. lift-up and move in a haphazard way.
It is due to a phenomenon called wake.
The separation of flow, and the difference of pressure on the upstream and downstream sides of the moving vehicle are responsible far the wake.
Wake is an undesired situation.
It should be avoided or minimized by proper profiling of the body.
The contouring of body should be such that the separation of flow does not occur, and the pressure difference is not much on the upstream and downstream sides.
To achieve it, the modern cars employ a rear spoiler that adds to aerodynamic styling of the body.
The formed wakes can be of different sizes according to shape of the body.
The magnitude of pressure drag depends on the size of the wake.
The size of the wake will be large in a body such as circular disc, in the above figure bluff body profile, having sharp edges than well-rounded bodies.
The wake and therefore the drag force are extremely small in case of streamlined body.
In a well streamlined object, the friction drag is larger than the pressure drag; even though the total drag is about 0.02 to 0.03 only to that of the circular disc.
Flow pattern around a streamlined body is shown in following Fig a. and the pressure distribution in Fig. b.
The term ρv2/2 is called the dynamic pressure of the flowing air.
Racing Car Profiling: The coefficient of drag depends on shape of the body in high
velocity air streams.
As compared to flat headed body in which C D = 0.85 at 300 kmph, this value is only 0.15 in sharp pointed projection of racing cars.
Hence the racing cars are made of the profile as shown in Fig.
The angle of attack α (Fig.) is an important geometrical quantity in streamlining a body profile.
The pressure distribution around such profiles are shown in these figures for a = - 8° to + 36°.
The lift coefficient is related to the angle of attack by
As we desire CL to be a minimum, preferably zero, hence the body should be aligned in front of the upstream air so that α = 0.
The drag coefficient varies little with the angle of attack.
Coefficient of Drag : The aerodynamically streamlined body of Fiat Uno car with an
outstanding drag coefficient of 0.30 is shown in Fig.
This stylish body is a result of intensive studies of fluid dynamics and wind tunnel testings.
In fact, such studies and testings are a continued process in better body profiling to obtain lower coefficient of drag.
Values of CD for different categories of vehicles and also for some specific vehicles are given in Table 3.2.