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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.