What is aerodynamics?Aerodynamics, from Greek aer (air) + (dynamics), is a

branch of dynamics concerned with studying the motion of air , particularly when it interacts with a solid object.

AERODYNAMIC CHARACTERISTICSDragThrustWeightLift

DRAG

Aerodynamic force that resists the motion of an object moving through a fluid.

Force caused by turbulent airflow around an object that opposes the forward motion of the object through a gas or fluid.

THRUST

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.

• Cars create thrust using engines. • If drag increases and/or thrust decreases the car will

slow down.

Thrust Continued….

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.

LIFT

A fluid flowing past the surface of a body exerts a force on it. 

Lift is the component of this force that is perpendicular to the oncoming flow direction.

Drag coefficient

Drag coefficient (commonly denoted as: cd) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water.

lower drag coefficient indicates the object will have less aerodynamic  or hydrodynamic drag.

The drag coefficient is always associated with a particular surface area.

Drag coefficient Continued…Fd is the drag force, which is by definition the force

component in the direction of the flow velocityρ is the mass density of the fluidv is the speed of the object relative to the fluid andA is the reference area.

Influence of flow characteristics on the operation of vehicles

Reduction of fuel consumption

More favorable comfort characteristics (noise, ventilating and cooling of passenger compartment)

Improvement of driving characteristics (stability, handling, traffic safety).

Aerodynamics In Cars

Drag on front endFrontal pressure is caused by the air

attempting to flow around the front of the carAs 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

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

FRONT END

Drag force v-s frontal area

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

REAR END

Rear vacuum is caused by the "hole“ left in the air as the car passes through it, the space directly behind the bus is "empty" or like a vacuum.

The air molecules attempt to fill in to this area but the car 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 .

REAR END

Tapering the rear in plan view‟, usually from the rear wheel arch backwards, „can produce a significant reduction in drag‟.

Approaches in vehicle aerodynamics

LIFT OR DOWNFORCE

Down force is the same as the lift, only it acts to press down, instead of lifting up.

SOFTWARES

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

commonly used software’s are ANSYS,CATIA.

ANALYSIS IN GAMBIENT AND FLUENT

Preparing geometry of domain and bodyMeshing of the body and DomainApplying edge boundary condition to body

and domainExport the mesh file to the fluentContours of static pressure Contours of velocity magnitude

Preparing geometry of domain and body

Meshing of the body and domain

Applying edge boundary condition to body and domain

Contours of static pressure

Contours of velocity magnitude

ANALYSIS A CAR BODY IN GAMBIENT AND FLUENTPreparing geometry of domain and bodyMeshing of the body and DomainApplying edge boundary condition to body

and domainExport the mesh file to the fluentContours of static pressure Contours of velocity magnitude

Meshing of the body and domain

Contours of static pressure

Contours of velocity magnitude

GRAPH FRONT PRESSURE VS DISTANCE

GRAPH REAR END PRESSURE VS DISTANCE

CONCLUSIONFrom the contour map of the static pressure

it is observed that the body experience high positive pressure at front end while negative pressure at rear end.