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UNIT 1:

History of Aerodynamic Car Design

These antiques cars demonstrate how little was known about vehicle aerodynamics in the

early part of the 20th century.

While scientists have more or less been aware of what it takes to create aerodynamic

shapes for a long time, it took a while for those principles to be applied to automobile

design.

There was nothing aerodynamic about the earliest cars. Take a look at Ford's seminal

Model T -- it looks more like a horse carriage minus the horses -- a very boxy design,

indeed. Many of these early cars didn't need to worry about aerodynamics because they

were relatively slow. However, some racing cars of the early 1900s incorporated tapering

and aerodynamic features to one degree or another.

In 1921, German inventor Edmund Rumpler created the Rumpler-Tropfenauto, which

translates into "tear-drop car." Based on the most aerodynamic shape in nature, the

teardrop, it had a Cd of just .27, but its unique looks never caught on with the public.

Only about 100 were made [source:Price].

On the American side, one of the biggest leaps ahead in aerodynamic design came in the

1930s with the Chrysler Airflow. Inspired by birds in flight, the Airflow was one of the

first cars designed with aerodynamics in mind. Though it used some unique construction

techniques and had a nearly 50-50-weight distribution (equal weight distribution between

the front and rear axles for improved handling), a Great Depression-weary public never

fell in love with its unconventional looks, and the car was considered a flop. Still, its

streamlined design was far ahead of its time.

As the 1950s and '60s came about, some of the biggest advancements in automobile

aerodynamics came from racing. Originally, engineers experimented with different

designs, knowing that streamlined shapes could help their cars go faster and handle better

at high speeds. That eventually evolved into a very precise science of crafting the most

aerodynamic race car possible. Front and rear spoilers, shovel-shaped noses, and aero kits

http://auto.howstuffworks.com/1908-1927-ford-model-t.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.europeancarweb.com/tech/0610_ec_aerodynamics_tech_buyers_guide/index.htmlhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.europeancarweb.com/tech/0610_ec_aerodynamics_tech_buyers_guide/index.htmlhttp://history.howstuffworks.com/american-history/prosperity-and-depression.htmhttp://auto.howstuffworks.com/1908-1927-ford-model-t.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.europeancarweb.com/tech/0610_ec_aerodynamics_tech_buyers_guide/index.htmlhttp://history.howstuffworks.com/american-history/prosperity-and-depression.htm

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became more and more common to keep air flowing over the top of the car and to create

necessary downforce on the front and rear wheels

On the consumer side, companies like Lotus, Citron and Porsche developed some very

streamlined designs, but these were mostly applied to high-performance sports cars andnot everyday vehicles for the common driver. That began to change in the 1980s with the

Audi 100, a passenger sedan with a then-unheard-of Cd of .30. Today, nearly all cars are

designed with aerodynamics in mind in some way

Fundamentals:

It's unpleasant to think about, but imagine what would happen if you drove your

car into a brick wall at 65 miles per hour (104.6 kilometers per hour). Metal would twist

and tear. Glass would shatter. Airbags would burst forth to protect you. But even with all

the advancements in safety we have on our modern automobiles, this would likely be a

tough accident to walk away from. A car simply isn't designed to go through a brick wall.

But there is another type of "wall" that cars are designed to move through, and have been

for a long time -- the wall of air that pushes against a vehicle at high speeds.

Most of us don't think of air or wind as a wall. At low speeds and on days when it's not

very windy outside, it's hard to notice the way air interacts with our vehicles. But at highspeeds, and on exceptionally windy days, air resistance (the forces acted upon a moving

object by the air -- also defined as drag) has a tremendous effect on the way a car

accelerates, handles and achieves fuel mileage.

This where the science of aerodynamics comes into play. Aerodynamics is the study of

forces and the resulting motion of objects through the air. For several decades, cars have

been designed with aerodynamics in mind, and carmakers have come up with a variety of

innovations that make cutting through that "wall" of air easier and less of an impact on

daily driving.

Essentially, having a car designed with airflow in mind means it has less difficulty

accelerating and can achieve better fuel economy numbers because the engine doesn't

have to work nearly as hard to push the car through the wall of air.

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Engineers have developed several ways of doing this. For instance, more rounded designs

and shapes on the exterior of the vehicle are crafted to channel air in a way so that it

flows around the car with the least resistance possible. Some high-performance cars even

have parts that move air smoothly across the underside of the car. Many also include a

spoiler -- also known as a rear wing -- to keep the air from lifting the car's wheels and

making it unstable at high speeds. Although, as you'll read later, most of the spoilers that

you see on cars are simply for decoration more than anything else.

In this article, we'll look at the physics of aerodynamics and air resistance, the history of

how cars have been designed with these factors in mind and how with the trend toward

"greener" cars, aerodynamics is now more important than ever.

Fundamentals of fluid mechanics:

The foundational axioms of fluid dynamics are the conservation laws,

specifically, conservation of mass, conservation of linear momentum (also known as

Newton's Second Law of Motion), and conservation of energy(also known as First Law

of Thermodynamics). These are based on classical mechanics and are modified in

quantum mechanics and general relativity. They are expressed using the Reynolds

Transport Theorem.

In addition to the above, fluids are assumed to obey the continuum assumption. Fluids are

composed of molecules that collide with one another and solid objects. However, the

continuum assumption considers fluids to be continuous, rather than discrete.

Consequently, properties such as density, pressure, temperature, and velocity are taken to

be well-defined at infinitesimally small points, and are assumed to vary continuously

from one point to another. The fact that the fluid is made up of discrete molecules is

ignored.

For fluids which are sufficiently dense to be a continuum, do not contain ionized species,

and have velocities small in relation to the speed of light, the momentum equations for

Newtonian fluids are theNavier-Stokes equations, which is a non-linearset ofdifferential

equations that describes the flow of a fluid whose stress depends linearly on velocity

http://en.wikipedia.org/wiki/Conservation_lawhttp://en.wikipedia.org/wiki/Conservation_of_masshttp://en.wikipedia.org/wiki/Conservation_of_momentumhttp://en.wikipedia.org/wiki/Newton's_laws_of_motionhttp://en.wikipedia.org/wiki/Conservation_of_energyhttp://en.wikipedia.org/wiki/Conservation_of_energyhttp://en.wikipedia.org/wiki/First_Law_of_Thermodynamicshttp://en.wikipedia.org/wiki/First_Law_of_Thermodynamicshttp://en.wikipedia.org/wiki/Classical_mechanicshttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/General_relativityhttp://en.wikipedia.org/wiki/Reynolds_transport_theoremhttp://en.wikipedia.org/wiki/Reynolds_transport_theoremhttp://en.wikipedia.org/wiki/Newtonian_fluidhttp://en.wikipedia.org/wiki/Navier-Stokes_equationshttp://en.wikipedia.org/wiki/Non-linearhttp://en.wikipedia.org/wiki/Non-linearhttp://en.wikipedia.org/wiki/Differential_equationshttp://en.wikipedia.org/wiki/Differential_equationshttp://en.wikipedia.org/wiki/Differential_equationshttp://en.wikipedia.org/wiki/Conservation_lawhttp://en.wikipedia.org/wiki/Conservation_of_masshttp://en.wikipedia.org/wiki/Conservation_of_momentumhttp://en.wikipedia.org/wiki/Newton's_laws_of_motionhttp://en.wikipedia.org/wiki/Conservation_of_energyhttp://en.wikipedia.org/wiki/First_Law_of_Thermodynamicshttp://en.wikipedia.org/wiki/First_Law_of_Thermodynamicshttp://en.wikipedia.org/wiki/Classical_mechanicshttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/General_relativityhttp://en.wikipedia.org/wiki/Reynolds_transport_theoremhttp://en.wikipedia.org/wiki/Reynolds_transport_theoremhttp://en.wikipedia.org/wiki/Newtonian_fluidhttp://en.wikipedia.org/wiki/Navier-Stokes_equationshttp://en.wikipedia.org/wiki/Non-linearhttp://en.wikipedia.org/wiki/Differential_equationshttp://en.wikipedia.org/wiki/Differential_equations

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gradients and pressure. The unsimplified equations do not have a general closed-form

solution, so they are primarily of use in Computational Fluid Dynamics. The equations

can be simplified in a number of ways, all of which make them easier to solve. Some of

them allow appropriate fluid dynamics problems to be solved in closed form.

In addition to the mass, momentum, and energy conservation equations, a

thermodynamical equation of state giving the pressure as a function of other

thermodynamic variables for the fluid is required to completely specify the problem. An

example of this would be theperfect gas equation of state:

where p is pressure, is density, Ru is the gas constant, M is the molar mass and T is

temperature.

Compressible vs incompressible flow

All fluids are compressible to some extent, that is changes in pressure or temperature will

result in changes in density. However, in many situations the changes in pressure and

temperature are sufficiently small that the changes in density are negligible. In this case

the flow can be modeled as an incompressible flow. Otherwise the more general

compressible flowequations must be used.

Mathematically, incompressibility is expressed by saying that the density of a fluid

parcel does not change as it moves in the flow field, i.e.,

where D / Dt is the substantial derivative, which is the sum of local and convective

derivatives. This additional constraint simplifies the governing equations, especially in

the case when the fluid has a uniform density.

For flow of gases, to determine whether to use compressible or incompressible fluid

dynamics, the Mach number of the flow is to be evaluated. As a rough guide,

compressible effects can be ignored at Mach numbers below approximately 0.3. For

liquids, whether the incompressible assumption is valid depends on the fluid properties

(specifically the critical pressure and temperature of the fluid) and the flow conditions

(how close to the critical pressure the actual flow pressure becomes). Acoustic problems

always require allowing compressibility, since sound waves are compression waves

involving changes in pressure and density of the medium through which they propagate.

http://en.wikipedia.org/wiki/Solution_in_closed_formhttp://en.wikipedia.org/wiki/Solution_in_closed_formhttp://en.wikipedia.org/wiki/Computational_Fluid_Dynamicshttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Ideal_gas_lawhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Gas_constanthttp://en.wikipedia.org/wiki/Molar_masshttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Compressibilityhttp://en.wikipedia.org/wiki/Incompressible_flowhttp://en.wikipedia.org/wiki/Incompressible_flowhttp://en.wikipedia.org/wiki/Compressible_flowhttp://en.wikipedia.org/wiki/Compressible_flowhttp://en.wikipedia.org/wiki/Substantial_derivativehttp://en.wikipedia.org/wiki/Substantial_derivativehttp://en.wikipedia.org/wiki/Convective_derivativehttp://en.wikipedia.org/wiki/Convective_derivativehttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Acousticshttp://en.wikipedia.org/wiki/Sound_waveshttp://en.wikipedia.org/wiki/Solution_in_closed_formhttp://en.wikipedia.org/wiki/Solution_in_closed_formhttp://en.wikipedia.org/wiki/Computational_Fluid_Dynamicshttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Ideal_gas_lawhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Densityhttp://en.wikipedia.org/wiki/Gas_constanthttp://en.wikipedia.org/wiki/Molar_masshttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Compressibilityhttp://en.wikipedia.org/wiki/Incompressible_flowhttp://en.wikipedia.org/wiki/Compressible_flowhttp://en.wikipedia.org/wiki/Substantial_derivativehttp://en.wikipedia.org/wiki/Convective_derivativehttp://en.wikipedia.org/wiki/Convective_derivativehttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Acousticshttp://en.wikipedia.org/wiki/Sound_waves

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Viscous vs inviscid flow

Viscous problems are those in which fluid friction has significant effects on the fluid

motion.

The Reynolds numbercan be used to evaluate whether viscous or inviscid equations areappropriate to the problem.

Stokes flow is flow at very low Reynolds numbers, such that inertial forces can be

neglected compared to viscous forces.

On the contrary, high Reynolds numbers indicate that the inertial forces are more

significant than the viscous (friction) forces. Therefore, we may assume the flow to be an

inviscid flow, an approximation in which we neglect viscosity at all, compared to inertial

terms.

This idea can work fairly well when the Reynolds number is high. However, certain

problems such as those involving solid boundaries, may require that the viscosity be

included. Viscosity often cannot be neglected near solid boundaries because the no-slip

condition can generate a thin region of large strain rate (known as Boundary layer) which

enhances the effect of even a small amount of viscosity, and thus generating vorticity.

Therefore, to calculate net forces on bodies (such as wings) we should use viscous flow

equations. As illustrated by d'Alembert's paradox, a body in an inviscid fluid willexperience no drag force. The standard equations of inviscid flow are the Euler equations.

Another often used model, especially in computational fluid dynamics, is to use the Euler

equations away from the body and the boundary layer equations, which incorporates

viscosity, in a region close to the body.

The Euler equations can be integrated along a streamline to get Bernoulli's equation.

When the flow is everywhere irrotational and inviscid, Bernoulli's equation can be used

throughout the flow field. Such flows are calledpotential flows.

http://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Stokes_flowhttp://en.wikipedia.org/wiki/Inviscid_flowhttp://en.wikipedia.org/wiki/Inviscid_flowhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/No-slip_conditionhttp://en.wikipedia.org/wiki/No-slip_conditionhttp://en.wikipedia.org/wiki/Boundary_layerhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Vorticityhttp://en.wikipedia.org/wiki/D'Alembert's_paradoxhttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Boundary_layerhttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Bernoulli's_equationhttp://en.wikipedia.org/wiki/Lamellar_fieldhttp://en.wikipedia.org/wiki/Potential_flowhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Stokes_flowhttp://en.wikipedia.org/wiki/Inviscid_flowhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/No-slip_conditionhttp://en.wikipedia.org/wiki/No-slip_conditionhttp://en.wikipedia.org/wiki/Boundary_layerhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Vorticityhttp://en.wikipedia.org/wiki/D'Alembert's_paradoxhttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Boundary_layerhttp://en.wikipedia.org/wiki/Euler_equationshttp://en.wikipedia.org/wiki/Bernoulli's_equationhttp://en.wikipedia.org/wiki/Lamellar_fieldhttp://en.wikipedia.org/wiki/Potential_flow

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Steady vs unsteady flow

Hydrodynamics simulation of the RayleighTaylor instability[2]

When all the time derivatives of a flow field vanish, the flow is considered to be a steady

flow. Otherwise, it is called unsteady. Whether a particular flow is steady or unsteady,

can depend on the chosen frame of reference. For instance, laminar flow over a sphere is

steady in the frame of reference that is stationary with respect to the sphere. In a frame of

reference that is stationary than the governing equations of the same problem without

taking advantage of the steadiness of the flow field.

Although strictly unsteady flows, time-periodic problems can often be solved by the same

techniques as steady flows. For this reason, they can be considered to be somewhere

between steady and unsteady.

Laminar versus turbulent flow

Turbulence is flow characterized by recirculation,eddies, and apparent randomness. Flow

in which turbulence is not exhibited is called laminar. It should be noted, however, that

the presence of eddies or recirculation alone does not necessarily indicate turbulent flow

these phenomena may be present in laminar flow as well. Mathematically, turbulent

flow is often represented via a Reynolds decomposition, in which the flow is broken

down into the sum of an average component and a perturbation component.

http://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instabilityhttp://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instabilityhttp://en.wikipedia.org/wiki/Fluid_flow#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Frame_of_referencehttp://en.wikipedia.org/wiki/Spherehttp://en.wikipedia.org/wiki/Turbulencehttp://en.wikipedia.org/wiki/Eddy_(fluid_dynamics)http://en.wikipedia.org/wiki/Eddy_(fluid_dynamics)http://en.wikipedia.org/wiki/Eddy_(fluid_dynamics)http://en.wikipedia.org/wiki/Randomhttp://en.wikipedia.org/wiki/Randomhttp://en.wikipedia.org/wiki/Laminar_flowhttp://en.wikipedia.org/wiki/Reynolds_decompositionhttp://en.wikipedia.org/wiki/Reynolds_decompositionhttp://en.wikipedia.org/wiki/Averagehttp://en.wikipedia.org/wiki/File:HD-Rayleigh-Taylor.gifhttp://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instabilityhttp://en.wikipedia.org/wiki/Fluid_flow#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Frame_of_referencehttp://en.wikipedia.org/wiki/Spherehttp://en.wikipedia.org/wiki/Turbulencehttp://en.wikipedia.org/wiki/Eddy_(fluid_dynamics)http://en.wikipedia.org/wiki/Randomhttp://en.wikipedia.org/wiki/Laminar_flowhttp://en.wikipedia.org/wiki/Reynolds_decompositionhttp://en.wikipedia.org/wiki/Average

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It is believed that turbulent flows can be described well through the use of the Navier

Stokes equations. Direct numerical simulation (DNS), based on the NavierStokes

equations, makes it possible to simulate turbulent flows at moderate Reynolds numbers.

Restrictions depend on the power of the computer used and the efficiency of the solution

algorithm. The results of DNS agree with the experimental data.

Most flows of interest have Reynolds numbers much too high for DNS to be a viable

option[3], given the state of computational power for the next few decades. Any flight

vehicle large enough to carry a human (L > 3 m), moving faster than 72 km/h (20 m/s) is

well beyond the limit of DNS simulation (Re = 4 million). Transport aircraft wings (such

as on anAirbus A300 orBoeing 747) have Reynolds numbers of 40 million (based on the

wing chord). In order to solve these real-life flow problems, turbulence models will be a

necessity for the foreseeable future. Reynolds-averaged NavierStokes equations

(RANS) combined with turbulence modeling provides a model of the effects of the

turbulent flow. Such a modeling mainly provides the additional momentum transfer by

theReynolds stresses, although the turbulence also enhances the heat andmass transfer.

Another promising methodology is large eddy simulation (LES), especially in the guise

of detached eddy simulation (DES)which is a combination of RANS turbulence

modeling and large eddy simulation.

Newtonian vs non-Newtonian fluids

Sir Isaac Newton showed how stress and the rate of strain are very close to linearly

related for many familiar fluids, such as water and air. These Newtonian fluids are

modeled by a coefficient calledviscosity, which depends on the specific fluid.

However, some of the other materials, such as emulsions and slurries and some visco-

elastic materials (eg. blood, some polymers), have more complicated non-Newtonian

stress-strain behaviours. These materials include sticky liquids such as latex,honey, and

lubricants which are studied in the sub-discipline ofrheology.

Subsonic vs transonic, supersonic and hypersonic flows

While many terrestrial flows (e.g. flow of water through a pipe) occur at low mach

numbers, many flows of practical interest (e.g. in aerodynamics) occur at high fractions

http://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Direct_numerical_simulationhttp://en.wikipedia.org/wiki/Fluid_flow#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/Airbus_A300http://en.wikipedia.org/wiki/Airbus_A300http://en.wikipedia.org/wiki/Boeing_747http://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Turbulence_modelinghttp://en.wikipedia.org/wiki/Reynolds_stresseshttp://en.wikipedia.org/wiki/Reynolds_stresseshttp://en.wikipedia.org/wiki/Reynolds_stresseshttp://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Mass_transferhttp://en.wikipedia.org/wiki/Mass_transferhttp://en.wikipedia.org/wiki/Large_eddy_simulationhttp://en.wikipedia.org/wiki/Detached_eddy_simulationhttp://en.wikipedia.org/wiki/Isaac_Newtonhttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Newtonian_fluidhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Non-Newtonian_fluidhttp://en.wikipedia.org/wiki/Latexhttp://en.wikipedia.org/wiki/Honeyhttp://en.wikipedia.org/wiki/Honeyhttp://en.wikipedia.org/wiki/Rheologyhttp://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Direct_numerical_simulationhttp://en.wikipedia.org/wiki/Fluid_flow#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/Airbus_A300http://en.wikipedia.org/wiki/Boeing_747http://en.wikipedia.org/wiki/Reynolds-averaged_Navier%E2%80%93Stokes_equationshttp://en.wikipedia.org/wiki/Turbulence_modelinghttp://en.wikipedia.org/wiki/Reynolds_stresseshttp://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Mass_transferhttp://en.wikipedia.org/wiki/Large_eddy_simulationhttp://en.wikipedia.org/wiki/Detached_eddy_simulationhttp://en.wikipedia.org/wiki/Isaac_Newtonhttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Strain_(materials_science)http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Newtonian_fluidhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Non-Newtonian_fluidhttp://en.wikipedia.org/wiki/Latexhttp://en.wikipedia.org/wiki/Honeyhttp://en.wikipedia.org/wiki/Rheology

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of the Mach Number M=1 or in excess of it (supersonic flows). New phenomena occur at

these Mach number regimes (e.g. shock waves for supersonic flow, transonic instability

in a regime of flows with M nearly equal to 1, non-equilibrium chemical behavior due to

ionization in hypersonic flows) and it is necessary to treat each of these flow regimes

separately.

Non-relativistic vs relativistic flows

Classical fluid dynamics is derived based on Newtonian mechanics, which is adequate for

most applications. However, at speeds comparable to the speed of light, c, Newtonian

mechanics is inaccurate and a relativistic framework has to be used instead.

External flow around a car:

External Flow around a Closed-Cabin Sports Car

The geometry consists of the external surfaces including underbody

components of the Jaguar XK8 sports car in the closed

configuration.

The Harpoon mesh contains 2.26M cells of all four cell types and

required 112 seconds to mesh on an AMD Opteron-based PC.

A steady flow simulation was performed on the same computer,

requiring 2 hours to converge.

The cell skew histogram is shown in figure 1. The plot of solution

residuals is shown in figure 2. Details of the geometry, surface

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pressure and flow streamlines are shown in figures 3 (a)-(d)

(geometry courtesy Jaguar)

External Flow around a Open-Cabin Sports Car

The geometry consists of the external surfaces including underbody

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Engine cooling:

The cooling system in most cars consists of the radiator and water pump. Water circulates

through passages around the cylinders and then travels through the radiator to cool it off.

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In a few cars (most notably Volkswagen Beetles), as well as most motorcycles and lawn

mowers, the engine is air-cooled instead (You can tell an air-cooled engine by the fins

adorning the outside of each cylinder to help dissipate heat.). Air-cooling makes the

engine lighter but hotter, generally decreasing engine life and overall performance. See

How Car Cooling Systems Work for details.

Diagram of a cooling system showing how all the plumbing is connected

So now you know how and why your engine stays cool. But why is air circulation so

important? Most cars are normally aspirated, which means that air flows through an air

filter and directly into the cylinders. High-performance engines are either turbocharged or

supercharged, which means that air coming into the engine is first pressurized (so that

more air/fuel mixture can be squeezed into each cylinder) to increase performance. The

amount of pressurization is called boost. A turbocharger uses a small turbine attached to

the exhaust pipe to spin a compressing turbine in the incoming air stream. A supercharger

is attached directly to the engine to spin the compressor.

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UNIT 2:

In fluid dynamics, drag (sometimes called air resistance or fluid resistance)

refers to forces that oppose the relative motion of an object through a fluid(a liquid or

gas). Drag forces act in a direction opposite to the oncoming flow velocity.[ Unlike other

resistive forces such as dry friction, which is nearly independent of velocity, drag forces

depend on velocity

For a solid object moving through a fluid, the drag is the component of the net

aerodynamic or hydrodynamic force acting opposite to the direction of the movement.

The component perpendicular to this direction is considered lift. Therefore drag opposes

the motion of the object, and in a powered vehicle it is overcome bythrust.

In astrodynamics, depending on the situation, atmospheric drag can be regarded as an

inefficiency requiring expense of additional energy during launch of the space object or

as a bonus simplifying return from orbit.

The drag equation calculates the force experienced by an object moving through a fluidat

relatively large velocity (i.e. high Reynolds number, Re > ~1000), also called quadratic

drag. The equation is attributed to Lord Rayleigh, who originally usedL2 in place ofA (L

being some length). The force on a moving object due to a fluid is:

Lift-induced drag (also called induced drag) is drag which occurs as the result of the

creation oflift on a three-dimensionallifting body, such as the wing or fuselage of an

airplane. Induced drag consists of two primary components, including drag due to the

creation of vortices (vortex drag) and the presence of additional viscous drag (lift-

induced viscous drag). The vortices in the flow-field, present in the wake of a lifting

body, derive from the turbulent mixing of air of varying pressure on the upper and lower

surfaces of the body, which is a necessary condition for the creation oflift.

With other parameters remaining the same, as the lift generated by a body increases, so

does the lift-induced drag. For an aircraft in flight, this means that as the angle of attack,

and therefore the lift, of the lifting body increases to the point of stall, so does the lift-

induced drag. At the onset of stall, lift is abruptly decreased, as is lift-induced drag, but

http://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Flow_velocityhttp://en.wikipedia.org/wiki/Net_forcehttp://en.wikipedia.org/wiki/Aerodynamic_forcehttp://en.wikipedia.org/wiki/Hydrodynamicshttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/wiki/Astrodynamicshttp://en.wikipedia.org/wiki/Space_launchhttp://en.wikipedia.org/wiki/Space_launchhttp://en.wikipedia.org/wiki/Drag_equationhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Lord_Rayleighhttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Lifting_bodyhttp://en.wikipedia.org/wiki/Lifting_bodyhttp://en.wikipedia.org/wiki/Lifting_bodyhttp://en.wikipedia.org/wiki/Winghttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Angle_of_attackhttp://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Flow_velocityhttp://en.wikipedia.org/wiki/Net_forcehttp://en.wikipedia.org/wiki/Aerodynamic_forcehttp://en.wikipedia.org/wiki/Hydrodynamicshttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/wiki/Astrodynamicshttp://en.wikipedia.org/wiki/Space_launchhttp://en.wikipedia.org/wiki/Drag_equationhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Lord_Rayleighhttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Lifting_bodyhttp://en.wikipedia.org/wiki/Winghttp://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Lift_(force)http://en.wikipedia.org/wiki/Angle_of_attack

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viscous pressure drag, a component of parasite drag, increases due to the formation of

turbulent unattached flow on the surface of the body.

The reference area A is often defined as the area of the orthographic projection of the

object on a plane perpendicular to the direction of motion e.g. for objects with a

simple shape, such as a sphere, this is the cross sectional area. Sometimes different

reference areas are given for the same object in which case a drag coefficient

corresponding to each of these different areas must be given.

In case of a wing, comparison of the drag to the lift force is easiest when the reference

areas are the same, since then the ratio of drag to lift force is just the ratio of drag to lift

coefficient.[4]

Therefore, the reference for a wing often is the planform (or wing) arearather than the frontal area.[5]

For an object with a smooth surface, and non-fixed separation points like a sphere or

circular cylinder the drag coefficient may vary with Reynolds numberRe, even up to

very high values (Re of the order 107). [6] [7] For an object with well-defined fixed

separation points, like a circular disk with its plane normal to the flow direction, the drag

coefficient is constant forRe > 3,500.[7] Further the drag coefficient Cd is, in general, a

function of the orientation of the flow with respect to the object (apart from symmetricalobjects like a sphere).

Power

Thepowerrequired to overcome the aerodynamic drag is given by:

Note that the power needed to push an object through a fluid increases as the cube of the

velocity. A car cruising on a highway at 50 mph (80 km/h) may require only

10 horsepower(7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h)

requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the

formula. Exerting four times the force over a fixed distance produces four times as much

work. At twice the speed the work (resulting in displacement over a fixed distance) is

done twice as fast. Since power is the rate of doing work, four times the work done in

half the time requires eight times the power.

http://en.wikipedia.org/wiki/Orthographic_projectionhttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Lift_forcehttp://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Drag_(physics)#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Planformhttp://en.wikipedia.org/wiki/Drag_(physics)#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Flow_separationhttp://en.wikipedia.org/wiki/Order_of_magnitudehttp://en.wikipedia.org/wiki/Drag_(physics)#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Drag_(physics)#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Drag_(physics)#cite_note-Batch341-6%23cite_note-Batch341-6http://en.wikipedia.org/wiki/Drag_(physics)#cite_note-Batch341-6%23cite_note-Batch341-6http://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Mechanical_workhttp://en.wikipedia.org/wiki/Orthographic_projectionhttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Lift_forcehttp://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Lift_coefficienthttp://en.wikipedia.org/wiki/Drag_(physics)#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Planformhttp://en.wikipedia.org/wiki/Drag_(physics)#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Flow_separationhttp://en.wikipedia.org/wiki/Order_of_magnitudehttp://en.wikipedia.org/wiki/Drag_(physics)#cite_note-5%23cite_note-5http://en.wikipedia.org/wiki/Drag_(physics)#cite_note-Batch341-6%23cite_note-Batch341-6http://en.wikipedia.org/wiki/Drag_(physics)#cite_note-Batch341-6%23cite_note-Batch341-6http://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Mechanical_work

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The Science of Aerodynamics

Before we look at how aerodynamics is applied to automobiles, here's a little physics

refresher course so that you can understand the basic idea.

As an object moves through the atmosphere, it displaces the air that surrounds it. The

object is also subjected to gravity and drag. Drag is generated when a solid object moves

through a fluid medium such as wateror air. Drag increases with velocity -- the faster the

object travels, the more drag it experiences.

We measure an object's motion using the factors described in Newton's laws. These

include mass, velocity, weight, external force, and acceleration.

Drag has a direct effect on acceleration. The acceleration (a) of an object is its weight

(W) minus drag (D) divided by its mass (m). Remember, weight is an object's mass times

the force of gravity acting on it. Your weight would change on the moon because of

lesser gravity, but your mass stays the same. To put it more simply:

a = (W - D) / m

(source:NASA)

As an object accelerates, its velocity and drag increase, eventually to the point where drag

becomes equal to weight -- in which case no further acceleration can occur. Let's say our

object in this equation is a car. This means that as the car travels faster and faster, more

and more air pushes against it, limiting how much more it can accelerate and restricting it

to a certain speed.

How does all of this apply to car design? Well, it's useful for figuring out an important

number -- drag coefficient. This is one of the primary factors that determine how easily

an object moves through the air. The drag coefficient (Cd) is equal to the drag (D),

divided by the quantity of the density (r), times half the velocity (V) squared times the

area (A). To make that more readable:

Cd = D / (A * .5 * r * V^2)

http://science.howstuffworks.com/physics-channel.htmhttp://science.howstuffworks.com/what-if-zero-gravity.htmhttp://science.howstuffworks.com/h2o.htmhttp://science.howstuffworks.com/newton-law-of-motion.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.grc.nasa.gov/WWW/K-12/airplane/falling.htmlhttp://science.howstuffworks.com/physics-channel.htmhttp://science.howstuffworks.com/what-if-zero-gravity.htmhttp://science.howstuffworks.com/h2o.htmhttp://science.howstuffworks.com/newton-law-of-motion.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.grc.nasa.gov/WWW/K-12/airplane/falling.html

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The Coefficient of Drag

The Toyota Prius' unique shape is one factor that helps it get incredible fuel economy.

We've just learned that the coefficient of drag (Cd) is a figure that measures the force of

air resistance on an object, such as a car. Now, imagine the force of air pushing against

the car as it moves down the road. At 70 miles per hour (112.7 kilometers per hour),

there's four times more force working against the car than at 35 miles per hour (56.3

kilometers per hour) [source: Elliott-Sink].

The aerodynamic abilities of a car are measured using the vehicle's coefficient of drag.

Essentially, the lower the Cd, the more aerodynamic a car is, and the easier it can move

through the wall of air pushing against it.

Let's look at a few Cd numbers. Remember the boxy old Volvo cars of the 1970s and

'80s? An old Volvo 960 sedan achieves a Cd of .36. The newer Volvos are much more

sleek and curvy, and an S80 sedan achieves a Cd of .28 [source: Elliott-Sink]. This

proves something that you may have been able to guess already -- smoother, more

streamlined shapes are more aerodynamic than boxy ones. Why is that exactly?

Let's look at the most aerodynamic thing in nature -- a teardrop. The teardrop is smooth

and round on all sides and tapers off at the top. Air flows around it smoothly as it falls to

the ground. It's the same with cars -- smooth, rounded surfaces allow the air to flow in a

stream over the vehicle, reducing the "push" of air against the body.

http://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.edmunds.com/advice/fueleconomy/articles/106954/article.htmlhttp://auto.howstuffworks.com/volvo-sports-cars.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.edmunds.com/advice/fueleconomy/articles/106954/article.htmlhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.edmunds.com/advice/fueleconomy/articles/106954/article.htmlhttp://auto.howstuffworks.com/volvo-sports-cars.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.edmunds.com/advice/fueleconomy/articles/106954/article.html

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Today, most cars achieve a Cd of about .30. SUVs, which tend to be more boxy than cars

because they're larger, accommodate more people, and often need bigger grilles to help

cool the engine down, have a Cd of anywhere from .30 to .40 or more. Pickup trucks -- a

purposefully boxy design -- typically get around .40 [source:Siuru].

Many have questioned the "unique" looks of the Toyota Prius hybrid, but it has an

extremely aerodynamic shape for a good reason. Among other efficient characteristics, its

Cd of .26 helps it achieve very high mileage. In fact, reducing the Cd of a car by just 0.01

can result in a 0.2 miles per gallon (.09 kilometers per liter) increase in fuel economy

The drag equation

Fd = cd 1/2 v2 A

is essentially a statement that the dragforce on any object is proportional to the density of

the fluid, and proportional to the square of the relative speed between the object and the

fluid.

Cd is not a constant but varies as a function of speed, flow direction, object shape, fluid

density and fluid viscosity. Speed, kinematic viscosity and a characteristiclength scale of

the object are incorporated into a dimensionless quantity called theReynolds numberor

Re. Cd is thus a function ofRe. In compressible flow, the speed of sound is relevant and

Cd is also a function ofMach numberMa.

For a certain body shape the drag coefficient Cd only depends on the Reynolds number

Re, Mach numberMa and the direction of the flow. For low Mach number Ma, as usual

for automobiles and sports planes, the drag coefficient is independent of Mach number.

Also the variation with Reynolds numberRe within a practical range of interest is usually

small, while for cars at highway speed and aircraft at cruising speed the incoming flow

direction is as well more-or-less the same. So the drag coefficient Cd can often be treated

as a constant. [8]

For a streamlined body to achieve a low drag coefficient the boundary layeraround the

body must remain attached to the surface of the body for as long as possible, causing the

wake to be narrow. A broad wake results in high form drag. The boundary layer will

remain attached longer if it is turbulent than if it is laminar. The boundary layer will

http://auto.howstuffworks.com/auto-parts/towing/towing-capacity/information/half-ton-truck.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.greencar.com/articles/5-facts-vehicle-aerodynamics.phphttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.greencar.com/articles/5-facts-vehicle-aerodynamics.phphttp://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Speedhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Kinematic_viscosityhttp://en.wikipedia.org/wiki/Length_scalehttp://en.wikipedia.org/wiki/Length_scalehttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Sports_planehttp://en.wikipedia.org/wiki/Drag_coefficient#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Boundary_layerhttp://en.wikipedia.org/wiki/Wakehttp://en.wikipedia.org/wiki/Wakehttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Laminarhttp://auto.howstuffworks.com/auto-parts/towing/towing-capacity/information/half-ton-truck.htmhttp://howstuffworks.com/framed.htm?parent=aerodynamics.htm&url=http://www.greencar.com/articles/5-facts-vehicle-aerodynamics.phphttp://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Speedhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Kinematic_viscosityhttp://en.wikipedia.org/wiki/Length_scalehttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Sports_planehttp://en.wikipedia.org/wiki/Drag_coefficient#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Boundary_layerhttp://en.wikipedia.org/wiki/Wakehttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Laminar

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Cd Item

0.9 a typicalbicycle plus cyclist

0.4 rough sphere (Re = 106)

0.1 smooth sphere (Re = 106)

0.001 laminar flat plate parallel to the flow (Re = 106)

0.005 turbulent flat plate parallel to the flow (Re = 106)

0.26 modern car (e.g. Toyota Prius[13])

0.295 bullet (not ogive, at subsonic velocity)

1.01.3 man (upright position)

1.28 flat plate perpendicular to flow

1.01.1 skier

1.01.3 wires and cables

1.1-1.3 ski jumper[13]

1.31.5 Empire State Building

1.82.0 Eiffel Tower

2.1 a smooth brick

>2.5 spacecraft in LEO

http://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Drag_coefficient#cite_note-tool-12%23cite_note-tool-12http://en.wikipedia.org/wiki/Ogivehttp://en.wikipedia.org/wiki/Skiinghttp://en.wikipedia.org/wiki/Drag_coefficient#cite_note-tool-12%23cite_note-tool-12http://en.wikipedia.org/wiki/Empire_State_Buildinghttp://en.wikipedia.org/wiki/Eiffel_Towerhttp://en.wikipedia.org/wiki/Low_Earth_Orbithttp://en.wikipedia.org/wiki/Drag_coefficienthttp://en.wikipedia.org/wiki/Bicyclehttp://en.wikipedia.org/wiki/Reynolds_numberhttp://en.wikipedia.org/wiki/Drag_coefficient#cite_note-tool-12%23cite_note-tool-12http://en.wikipedia.org/wiki/Ogivehttp://en.wikipedia.org/wiki/Skiinghttp://en.wikipedia.org/wiki/Drag_coefficient#cite_note-tool-12%23cite_note-tool-12http://en.wikipedia.org/wiki/Empire_State_Buildinghttp://en.wikipedia.org/wiki/Eiffel_Towerhttp://en.wikipedia.org/wiki/Low_Earth_Orbit

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Production cars

Cd Automobile Year

0.7 to 1.1typical values for a Formula 1 car (downforce settings change for each

circuit)0.74 Legends Car

0.7 Caterham Seven

0.6 + a typicaltruck

0.57 Hummer H2 2003

0.51 Citron 2CV 1948

0.48 Volkswagen Beetle (newer models) [1][2]

0.47 Lancia Aprilia 1937

http://en.wikipedia.org/wiki/Formula_1http://en.wikipedia.org/wiki/Downforcehttp://en.wikipedia.org/w/index.php?title=Legends_Car&action=edit&redlink=1http://en.wikipedia.org/wiki/Caterham_Sevenhttp://en.wikipedia.org/wiki/Truckhttp://en.wikipedia.org/wiki/Truckhttp://en.wikipedia.org/wiki/Hummer_H2http://en.wikipedia.org/wiki/Citro%C3%ABn_2CVhttp://en.wikipedia.org/wiki/Volkswagen_Beetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Lancia_Apriliahttp://en.wikipedia.org/wiki/Automobile_drag_coefficienthttp://en.wikipedia.org/wiki/Automobile_drag_coefficienthttp://en.wikipedia.org/wiki/Automobile_drag_coefficienthttp://en.wikipedia.org/wiki/Formula_1http://en.wikipedia.org/wiki/Downforcehttp://en.wikipedia.org/w/index.php?title=Legends_Car&action=edit&redlink=1http://en.wikipedia.org/wiki/Caterham_Sevenhttp://en.wikipedia.org/wiki/Truckhttp://en.wikipedia.org/wiki/Hummer_H2http://en.wikipedia.org/wiki/Citro%C3%ABn_2CVhttp://en.wikipedia.org/wiki/Volkswagen_Beetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-1%23cite_note-1http://en.wikipedia.org/wiki/Lancia_Aprilia

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0.46 Ford Mustang (coupe) 1979

0.45 Dodge ViperRT/10 1996

0.44 Ford Mustang (fastback) 1979

0.44 Peugeot 305 1978

0.44 Peugeot 504 1968

0.44 Toyota Truck 1990

0.425Duple425 coach(named for its low Cd by coach standards)

c.1985

0.42 Lamborghini Countach 1974

0.42 Triumph Spitfire Mk IV 1971

0.42 Plymouth Duster 1994

0.41 Volvo 740(sedan) 1982

0.40 Ford Escape Hybrid 2005

0.40 Nissan Skyline GT-RR32 1989

0.39 Dodge Durango 2004

0.39 Chevrolet Tahoe 2006

0.39 Triumph Spitfire 1964

0.38 Volkswagen Beetle (original design)[3] 1938

0.38VW NewBeetle[4]

without wing or spoiler 0.39[5]2003

0.385 Nissan 280ZX 1978

0.38 Mazda Miata 1989

0.374 Ford Capri Mk III 1978

0.372 Ferrari F50 1996

0.37 Renault Twingo

0.37 BMW Z3 M coupe 1999

0.37 Volkswagen Tiguan 20080.36 Cadillac Escalade hybrid 2008

0.36 Cadillac Fleetwood 1996

0.36 Citron CX(named after the term for Cd) 1974

0.36 Citron DS 1955

0.36 Chrysler Sebring 1996

0.36 Ferrari Testarossa 1986

0.36 Ford Mustang 1999

0.36 Honda Civic 2001

0.36 Opel GT 1969

0.355 NSU Ro 80 19670.35 Aston Martin Vanquish 2004

0.35 BMW Z4 M coupe 2006

0.35 Dodge Viper GTS 1996

0.35 Jaguar XKR 2005

0.35 Lexus RX 2003-2009

0.35 MINI Cooper 2008

0.35 Tesla Roadster[6] 2008

http://en.wikipedia.org/wiki/Ford_Mustanghttp://en.wikipedia.org/wiki/Dodge_Viperhttp://en.wikipedia.org/wiki/Ford_Mustanghttp://en.wikipedia.org/wiki/Peugeot_305http://en.wikipedia.org/wiki/Peugeot_504http://en.wikipedia.org/wiki/Toyota_Truckhttp://en.wikipedia.org/wiki/Duple_Coachbuildershttp://en.wikipedia.org/wiki/Duple_Coachbuildershttp://en.wikipedia.org/wiki/Lamborghini_Countachhttp://en.wikipedia.org/wiki/Triumph_Spitfirehttp://en.wikipedia.org/wiki/Plymouth_Dusterhttp://en.wikipedia.org/wiki/Volvo_740http://en.wikipedia.org/wiki/Volvo_740http://en.wikipedia.org/wiki/Ford_Escape_Hybridhttp://en.wikipedia.org/wiki/Nissan_Skyline_GT-Rhttp://en.wikipedia.org/wiki/Nissan_Skyline_GT-Rhttp://en.wikipedia.org/wiki/Dodge_Durangohttp://en.wikipedia.org/wiki/Chevrolet_Tahoehttp://en.wikipedia.org/wiki/Triumph_Spitfirehttp://en.wikipedia.org/wiki/Volkswagen_Beetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/VW_NewBeetlehttp://en.wikipedia.org/wiki/VW_NewBeetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Nissan_280ZXhttp://en.wikipedia.org/wiki/Mazda_Miatahttp://en.wikipedia.org/wiki/Ford_Caprihttp://en.wikipedia.org/wiki/Ferrari_F50http://en.wikipedia.org/wiki/Renault_Twingohttp://en.wikipedia.org/wiki/BMW_Z3http://en.wikipedia.org/wiki/Volkswagen_Tiguanhttp://en.wikipedia.org/wiki/Cadillac_Escaladehttp://en.wikipedia.org/wiki/Cadillac_Fleetwoodhttp://en.wikipedia.org/wiki/Citro%C3%ABn_CXhttp://en.wikipedia.org/wiki/Citro%C3%ABn_DShttp://en.wikipedia.org/wiki/Chrysler_Sebringhttp://en.wikipedia.org/wiki/Ferrari_Testarossahttp://en.wikipedia.org/wiki/Ford_Mustanghttp://en.wikipedia.org/wiki/Honda_Civichttp://en.wikipedia.org/wiki/Opel_GThttp://en.wikipedia.org/wiki/NSU_Ro_80http://en.wikipedia.org/wiki/Aston_Martin_Vanquishhttp://en.wikipedia.org/wiki/BMW_Z4http://en.wikipedia.org/wiki/Dodge_Viper_GTShttp://en.wikipedia.org/wiki/Jaguar_XKRhttp://en.wikipedia.org/wiki/Lexus_RXhttp://en.wikipedia.org/wiki/MINI_Cooperhttp://en.wikipedia.org/wiki/Tesla_Roadsterhttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-Ramsey2009-5%23cite_note-Ramsey2009-5http://en.wikipedia.org/wiki/Ford_Mustanghttp://en.wikipedia.org/wiki/Dodge_Viperhttp://en.wikipedia.org/wiki/Ford_Mustanghttp://en.wikipedia.org/wiki/Peugeot_305http://en.wikipedia.org/wiki/Peugeot_504http://en.wikipedia.org/wiki/Toyota_Truckhttp://en.wikipedia.org/wiki/Duple_Coachbuildershttp://en.wikipedia.org/wiki/Lamborghini_Countachhttp://en.wikipedia.org/wiki/Triumph_Spitfirehttp://en.wikipedia.org/wiki/Plymouth_Dusterhttp://en.wikipedia.org/wiki/Volvo_740http://en.wikipedia.org/wiki/Ford_Escape_Hybridhttp://en.wikipedia.org/wiki/Nissan_Skyline_GT-Rhttp://en.wikipedia.org/wiki/Dodge_Durangohttp://en.wikipedia.org/wiki/Chevrolet_Tahoehttp://en.wikipedia.org/wiki/Triumph_Spitfirehttp://en.wikipedia.org/wiki/Volkswagen_Beetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-2%23cite_note-2http://en.wikipedia.org/wiki/VW_NewBeetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-3%23cite_note-3http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-4%23cite_note-4http://en.wikipedia.org/wiki/Nissan_280ZXhttp://en.wikipedia.org/wiki/Mazda_Miatahttp://en.wikipedia.org/wiki/Ford_Caprihttp://en.wikipedia.org/wiki/Ferrari_F50http://en.wikipedia.org/wiki/Renault_Twingohttp://en.wikipedia.org/wiki/BMW_Z3http://en.wikipedia.org/wiki/Volkswagen_Tiguanhttp://en.wikipedia.org/wiki/Cadillac_Escaladehttp://en.wikipedia.org/wiki/Cadillac_Fleetwoodhttp://en.wikipedia.org/wiki/Citro%C3%ABn_CXhttp://en.wikipedia.org/wiki/Citro%C3%ABn_DShttp://en.wikipedia.org/wiki/Chrysler_Sebringhttp://en.wikipedia.org/wiki/Ferrari_Testarossahttp://en.wikipedia.org/wiki/Ford_Mustanghttp://en.wikipedia.org/wiki/Honda_Civichttp://en.wikipedia.org/wiki/Opel_GThttp://en.wikipedia.org/wiki/NSU_Ro_80http://en.wikipedia.org/wiki/Aston_Martin_Vanquishhttp://en.wikipedia.org/wiki/BMW_Z4http://en.wikipedia.org/wiki/Dodge_Viper_GTShttp://en.wikipedia.org/wiki/Jaguar_XKRhttp://en.wikipedia.org/wiki/Lexus_RXhttp://en.wikipedia.org/wiki/MINI_Cooperhttp://en.wikipedia.org/wiki/Tesla_Roadsterhttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-Ramsey2009-5%23cite_note-Ramsey2009-5

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0.35 Toyota MR-2 1998

0.35 Toyota Sequoia 2007

0.35 Volvo 940(sedan) 1990

0.35 SSC Ultimate Aero 2007-Present

0.34 Aston Martin DB9 2004

0.34 Chevrolet Caprice 19940.34 Chevrolet Tahoe hybrid 2008

0.34 Ferrari F40 1987

0.34 Ferrari 360 Modena 1999

0.34 Ferrari F430 F1 2004

0.34 Ford Sierra 1982

0.34 Ford Puma 1997

0.34 Honda Prelude 1988

0.34 Mercedes-Benz SL (Roof Down) 2001

0.34 Peugeot 106 1991

0.34 Toyota Supra (with factory 3 piece turbo wing) 1989-19900.338 Chevrolet Camaro 1995

0.33 Audi A3 2006

0.33 Citron SM 1970

0.33 Dodge Charger 2006

0.33 Ford Crown Victoria 1992

0.33 Honda Accord Sedan 2002

0.33 Lamborghini Murcielago 2001

0.33 Lexus RX 2009

0.33 Mazda RX-7 FC3C 1987

0.33 Peugeot 206 1998

0.33 Peugeot 309 1986

0.33 Renault Modus 2004

0.33 Subaru Impreza WRX STi 2004

0.33 Toyota Supra (without wing) 1989-1990

0.324 Cobalt SS Supercharged 2005

0.32 AMC Pacer 1975-1980

0.32 Buick Riviera 1995

0.32 Dodge Avenger 1995

0.32 Honda Accord Coupe 2002

0.32 Honda NSX 1990

0.32 Mazdaspeed3 20070.32 McLaren F1 1992

0.32 Mercedes-Benz 190E 2.5-16/2.3-16

0.32 Nissan 300ZX 1989

0.32 Nissan Maxima 1997

0.32 Porsche 997 GT2

0.32 Peugeot 406 1995

http://en.wikipedia.org/wiki/Toyota_MR-2http://en.wikipedia.org/wiki/Toyota_Sequoiahttp://en.wikipedia.org/wiki/Volvo_940http://en.wikipedia.org/wiki/Volvo_940http://en.wikipedia.org/wiki/SSC_Ultimate_Aerohttp://en.wikipedia.org/wiki/Aston_Martin_DB9http://en.wikipedia.org/wiki/Chevrolet_Capricehttp://en.wikipedia.org/wiki/Chevrolet_Tahoehttp://en.wikipedia.org/wiki/Ferrari_F40http://en.wikipedia.org/wiki/Ferrari_360_Modenahttp://en.wikipedia.org/wiki/Ferrari_F430http://en.wikipedia.org/wiki/Ford_Sierrahttp://en.wikipedia.org/wiki/Ford_Pumahttp://en.wikipedia.org/wiki/Honda_Preludehttp://en.wikipedia.org/wiki/Mercedes-Benz_SLhttp://en.wikipedia.org/wiki/Peugeot_106http://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Chevrolet_Camarohttp://en.wikipedia.org/wiki/Audi_A3http://en.wikipedia.org/wiki/Citro%C3%ABn_SMhttp://en.wikipedia.org/wiki/Dodge_Charger_(LX)http://en.wikipedia.org/wiki/Ford_Crown_Victoriahttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Lamborghini_Murcielagohttp://en.wikipedia.org/wiki/Lexus_RXhttp://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Peugeot_206http://en.wikipedia.org/wiki/Peugeot_309http://en.wikipedia.org/wiki/Renault_Modushttp://en.wikipedia.org/wiki/Subaru_Impreza_WRX_STihttp://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Chevrolet_Cobalthttp://en.wikipedia.org/wiki/AMC_Pacerhttp://en.wikipedia.org/wiki/Buick_Rivierahttp://en.wikipedia.org/wiki/Dodge_Avengerhttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Honda_NSXhttp://en.wikipedia.org/wiki/Mazdaspeed3http://en.wikipedia.org/wiki/McLaren_F1http://en.wikipedia.org/wiki/Mercedes-Benz_W201http://en.wikipedia.org/wiki/Nissan_300ZXhttp://en.wikipedia.org/wiki/Nissan_Maximahttp://en.wikipedia.org/wiki/Porsche_997_GT2http://en.wikipedia.org/wiki/Peugeot_406http://en.wikipedia.org/wiki/Toyota_MR-2http://en.wikipedia.org/wiki/Toyota_Sequoiahttp://en.wikipedia.org/wiki/Volvo_940http://en.wikipedia.org/wiki/SSC_Ultimate_Aerohttp://en.wikipedia.org/wiki/Aston_Martin_DB9http://en.wikipedia.org/wiki/Chevrolet_Capricehttp://en.wikipedia.org/wiki/Chevrolet_Tahoehttp://en.wikipedia.org/wiki/Ferrari_F40http://en.wikipedia.org/wiki/Ferrari_360_Modenahttp://en.wikipedia.org/wiki/Ferrari_F430http://en.wikipedia.org/wiki/Ford_Sierrahttp://en.wikipedia.org/wiki/Ford_Pumahttp://en.wikipedia.org/wiki/Honda_Preludehttp://en.wikipedia.org/wiki/Mercedes-Benz_SLhttp://en.wikipedia.org/wiki/Peugeot_106http://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Chevrolet_Camarohttp://en.wikipedia.org/wiki/Audi_A3http://en.wikipedia.org/wiki/Citro%C3%ABn_SMhttp://en.wikipedia.org/wiki/Dodge_Charger_(LX)http://en.wikipedia.org/wiki/Ford_Crown_Victoriahttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Lamborghini_Murcielagohttp://en.wikipedia.org/wiki/Lexus_RXhttp://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Peugeot_206http://en.wikipedia.org/wiki/Peugeot_309http://en.wikipedia.org/wiki/Renault_Modushttp://en.wikipedia.org/wiki/Subaru_Impreza_WRX_STihttp://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Chevrolet_Cobalthttp://en.wikipedia.org/wiki/AMC_Pacerhttp://en.wikipedia.org/wiki/Buick_Rivierahttp://en.wikipedia.org/wiki/Dodge_Avengerhttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Honda_NSXhttp://en.wikipedia.org/wiki/Mazdaspeed3http://en.wikipedia.org/wiki/McLaren_F1http://en.wikipedia.org/wiki/Mercedes-Benz_W201http://en.wikipedia.org/wiki/Nissan_300ZXhttp://en.wikipedia.org/wiki/Nissan_Maximahttp://en.wikipedia.org/wiki/Porsche_997_GT2http://en.wikipedia.org/wiki/Peugeot_406

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0.32 Peugeot 806 1994

0.32 Scion xB 2008

0.32 Suzuki Swift 1991

0.32 Toyota Celica 1994

0.32 Toyota Supra (N/A with wing and turbo models) 1993

0.32 Toyota Supra (with factory turbo wing) 1987-19880.32 Volkswagen GTI Mk V 2006

0.31 Audi A4 B5 1995

0.31 BMW 7-series 2009

0.31 Buick Park Avenue 1996

0.31 Cadillac CTS-V 2005

0.31 Chevrolet C6 Corvette Z06

0.31 Citron AX 1986

0.31 Citron GS 1970

0.31 Eagle Vision 1995

0.31 Ford Falcon 19950.31 Holden Commodore 1998

0.31 Honda Civic (Sedan) 2006

0.310 Lamborghini Diablo 1990

0.31 Mazda RX-7 FC3S 1986

0.31 Mazda RX-7 FD R1(R2) 1993

0.31 Mazda RX-8 2004

0.31 Nissan Tiida / Versa 2004

0.31 Peugeot 307 2001

0.31 Porsche 997 Turbo/GT3 2006

0.31 Renault 25 1984

0.31 Saab Sonett III 1970

0.31 Scion xA 2004

0.31 Toyota Avalon 1995-2000

0.31 Toyota RAV4 2006

0.31 Toyota Supra (N/A; without factory wing) 1993

0.31 Volkswagen GTI Mk IV 1997

0.30 Honda NSX 2002

0.30 Audi 100 1983

0.30 BMW E90 2006

0.30 Hyundai Sonata 2006

0.30 Honda Accord Sedan 2003, 2005-20070.30 Honda Odyssey 2005

0.30 Koenigsegg CCX 2006

0.30 Mitsubishi Eclipse 2000

0.30 Nissan 180SX 1989

0.30 Nissan 300ZX 1983

0.30 Nissan 350Z Coupe Base and Enthusiast models 2003-2008

http://en.wikipedia.org/wiki/Peugeot_806http://en.wikipedia.org/wiki/Scion_xBhttp://en.wikipedia.org/wiki/Suzuki_Cultushttp://en.wikipedia.org/wiki/Toyota_Celicahttp://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Volkswagen_GTI#Mark_5http://en.wikipedia.org/wiki/Audi_A4#B5_A4_.288D.29_.281994.E2.80.932001.29http://en.wikipedia.org/wiki/BMW_7-serieshttp://en.wikipedia.org/wiki/Buick_Park_Avenuehttp://en.wikipedia.org/wiki/Cadillac_CTS-Vhttp://en.wikipedia.org/wiki/Citro%C3%ABn_AXhttp://en.wikipedia.org/wiki/Citro%C3%ABn_GShttp://en.wikipedia.org/wiki/Eagle_Visionhttp://en.wikipedia.org/wiki/Ford_Falcon_(Australia)http://en.wikipedia.org/wiki/Holden_Commodorehttp://en.wikipedia.org/wiki/Honda_Civichttp://en.wikipedia.org/wiki/Lamborghini_Diablohttp://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mazda_RX-8http://en.wikipedia.org/wiki/Nissan_Tiidahttp://en.wikipedia.org/wiki/Peugeot_307http://en.wikipedia.org/wiki/Porsche_997http://en.wikipedia.org/wiki/Renault_25http://en.wikipedia.org/wiki/Saab_Sonetthttp://en.wikipedia.org/wiki/Scion_xAhttp://en.wikipedia.org/wiki/Toyota_Avalonhttp://en.wikipedia.org/wiki/Toyota_RAV4http://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Volkswagen_GTI#Mark_4http://en.wikipedia.org/wiki/Honda_NSXhttp://en.wikipedia.org/wiki/Audi_100http://en.wikipedia.org/wiki/BMW_E90http://en.wikipedia.org/wiki/Hyundai_Sonatahttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Honda_Odysseyhttp://en.wikipedia.org/wiki/Koenigsegg_CCXhttp://en.wikipedia.org/wiki/Mitsubishi_Eclipsehttp://en.wikipedia.org/wiki/Nissan_180SXhttp://en.wikipedia.org/wiki/Nissan_300ZXhttp://en.wikipedia.org/wiki/Peugeot_806http://en.wikipedia.org/wiki/Scion_xBhttp://en.wikipedia.org/wiki/Suzuki_Cultushttp://en.wikipedia.org/wiki/Toyota_Celicahttp://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Volkswagen_GTI#Mark_5http://en.wikipedia.org/wiki/Audi_A4#B5_A4_.288D.29_.281994.E2.80.932001.29http://en.wikipedia.org/wiki/BMW_7-serieshttp://en.wikipedia.org/wiki/Buick_Park_Avenuehttp://en.wikipedia.org/wiki/Cadillac_CTS-Vhttp://en.wikipedia.org/wiki/Citro%C3%ABn_AXhttp://en.wikipedia.org/wiki/Citro%C3%ABn_GShttp://en.wikipedia.org/wiki/Eagle_Visionhttp://en.wikipedia.org/wiki/Ford_Falcon_(Australia)http://en.wikipedia.org/wiki/Holden_Commodorehttp://en.wikipedia.org/wiki/Honda_Civichttp://en.wikipedia.org/wiki/Lamborghini_Diablohttp://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mazda_RX-8http://en.wikipedia.org/wiki/Nissan_Tiidahttp://en.wikipedia.org/wiki/Peugeot_307http://en.wikipedia.org/wiki/Porsche_997http://en.wikipedia.org/wiki/Renault_25http://en.wikipedia.org/wiki/Saab_Sonetthttp://en.wikipedia.org/wiki/Scion_xAhttp://en.wikipedia.org/wiki/Toyota_Avalonhttp://en.wikipedia.org/wiki/Toyota_RAV4http://en.wikipedia.org/wiki/Toyota_Suprahttp://en.wikipedia.org/wiki/Volkswagen_GTI#Mark_4http://en.wikipedia.org/wiki/Honda_NSXhttp://en.wikipedia.org/wiki/Audi_100http://en.wikipedia.org/wiki/BMW_E90http://en.wikipedia.org/wiki/Hyundai_Sonatahttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Honda_Odysseyhttp://en.wikipedia.org/wiki/Koenigsegg_CCXhttp://en.wikipedia.org/wiki/Mitsubishi_Eclipsehttp://en.wikipedia.org/wiki/Nissan_180SXhttp://en.wikipedia.org/wiki/Nissan_300ZX

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0.30Nissan 370Z Coupe(0.29 with sport package)

2008

0.30 Renault 19 16V 1991

0.30 Saab 92 1947

0.30 Toyota Sienna 2003-2009

0.295 Ford Falcon 19980.29 Alfa Romeo 155 1992

0.29 BMW 8-Series 1989

0.29 Chevrolet Corvette 2005

0.29 Chevrolet Corvette C5 Z06 2002

0.29 Daewoo Espero 1990

0.29 Dodge Charger Daytona 1969

0.29 Eagle Talon 1990s [2]

0.29 Honda Accord Hybrid 2005, 2007

0.29 Honda Accord Coupe 2003, 2005-2007

0.29 Honda CRX HF 1988

0.29 Infiniti G35 Sedan 2008

0.29 Lancia Dedra 1990

0.29 Lexus LS 400 1990

0.29 Lotus Elite 1958

0.29 Lotus Europa 1966

0.29 Mazda Millenia 1995

0.29 Mazda RX-7 FC3S Aero Package 1986

0.29 Mazda 3 2010

0.29 Mazda RX-7 FD 1993

0.29 Mercedes-Benz SL (Roof Up) 2001

0.29 Mercedes-Benz W203C-Class Coupe 20010.29 Nissan 350Z Coupe Track and Grand Touring 2007-2008

0.29 Nissan Versa 2007-2008

0.29 Peugeot 308 2007

0.29 Peugeot 407 2004

0.29 Peugeot 607 1999

0.29 Porsche Boxster 2005

0.29 Subaru XT 1985

0.29 Subaru SVX 1992

0.29 Toyota Camry 1996-2001

0.291 Toyota Avalon 20050.29 Toyota Prius 2001

0.28 Chevrolet Corvette C6 2006

0.28 Citron XM 1989

0.28 Citron C4 2004

0.28 Lexus IS 2006

0.28 Mitsubishi Diamante 1995

http://en.wikipedia.org/wiki/Nissan_370Zhttp://en.wikipedia.org/wiki/Nissan_370Zhttp://en.wikipedia.org/wiki/Renault_19http://en.wikipedia.org/wiki/Saab_92http://en.wikipedia.org/wiki/Toyota_Siennahttp://en.wikipedia.org/wiki/Ford_Falcon_(Australia)http://en.wikipedia.org/wiki/Alfa_Romeo_155http://en.wikipedia.org/wiki/BMW_8-Serieshttp://en.wikipedia.org/wiki/Chevrolet_Corvettehttp://en.wikipedia.org/wiki/Chevrolet_Corvette_C5_Z06http://en.wikipedia.org/wiki/Daewoo_Esperohttp://en.wikipedia.org/wiki/Dodge_Charger_Daytonahttp://en.wikipedia.org/wiki/Eagle_Talonhttp://en.wikipedia.org/wiki/Honda_Accord_Hybridhttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Honda_CRXhttp://en.wikipedia.org/wiki/Infiniti_G35http://en.wikipedia.org/wiki/Lancia_Dedrahttp://en.wikipedia.org/wiki/Lexus_LS_400http://en.wikipedia.org/wiki/Lotus_Elitehttp://en.wikipedia.org/wiki/Lotus_Europahttp://en.wikipedia.org/wiki/Mazda_Milleniahttp://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mazda_3http://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mercedes-Benz_SLhttp://en.wikipedia.org/wiki/Mercedes-Benz_W203http://en.wikipedia.org/wiki/Mercedes-Benz_C-Classhttp://en.wikipedia.org/wiki/Mercedes-Benz_C-Classhttp://en.wikipedia.org/w/index.php?title=Nissan_350Z_Coupe_Track_and_Grand_Touring&action=edit&redlink=1http://en.wikipedia.org/wiki/Nissan_Versahttp://en.wikipedia.org/wiki/Peugeot_308http://en.wikipedia.org/wiki/Peugeot_407http://en.wikipedia.org/wiki/Peugeot_607http://en.wikipedia.org/wiki/Porsche_Boxsterhttp://en.wikipedia.org/wiki/Subaru_XThttp://en.wikipedia.org/wiki/Subaru_SVXhttp://en.wikipedia.org/wiki/Toyota_Camryhttp://en.wikipedia.org/wiki/Toyota_Avalonhttp://en.wikipedia.org/wiki/Toyota_Priushttp://en.wikipedia.org/wiki/Chevrolet_Corvette_C6http://en.wikipedia.org/wiki/Citro%C3%ABn_XMhttp://en.wikipedia.org/wiki/Citro%C3%ABn_C4http://en.wikipedia.org/wiki/Lexus_IShttp://en.wikipedia.org/wiki/Mitsubishi_Diamantehttp://en.wikipedia.org/wiki/Nissan_370Zhttp://en.wikipedia.org/wiki/Nissan_370Zhttp://en.wikipedia.org/wiki/Renault_19http://en.wikipedia.org/wiki/Saab_92http://en.wikipedia.org/wiki/Toyota_Siennahttp://en.wikipedia.org/wiki/Ford_Falcon_(Australia)http://en.wikipedia.org/wiki/Alfa_Romeo_155http://en.wikipedia.org/wiki/BMW_8-Serieshttp://en.wikipedia.org/wiki/Chevrolet_Corvettehttp://en.wikipedia.org/wiki/Chevrolet_Corvette_C5_Z06http://en.wikipedia.org/wiki/Daewoo_Esperohttp://en.wikipedia.org/wiki/Dodge_Charger_Daytonahttp://en.wikipedia.org/wiki/Eagle_Talonhttp://en.wikipedia.org/wiki/Honda_Accord_Hybridhttp://en.wikipedia.org/wiki/Honda_Accordhttp://en.wikipedia.org/wiki/Honda_CRXhttp://en.wikipedia.org/wiki/Infiniti_G35http://en.wikipedia.org/wiki/Lancia_Dedrahttp://en.wikipedia.org/wiki/Lexus_LS_400http://en.wikipedia.org/wiki/Lotus_Elitehttp://en.wikipedia.org/wiki/Lotus_Europahttp://en.wikipedia.org/wiki/Mazda_Milleniahttp://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mazda_3http://en.wikipedia.org/wiki/Mazda_RX-7http://en.wikipedia.org/wiki/Mercedes-Benz_SLhttp://en.wikipedia.org/wiki/Mercedes-Benz_W203http://en.wikipedia.org/wiki/Mercedes-Benz_C-Classhttp://en.wikipedia.org/w/index.php?title=Nissan_350Z_Coupe_Track_and_Grand_Touring&action=edit&redlink=1http://en.wikipedia.org/wiki/Nissan_Versahttp://en.wikipedia.org/wiki/Peugeot_308http://en.wikipedia.org/wiki/Peugeot_407http://en.wikipedia.org/wiki/Peugeot_607http://en.wikipedia.org/wiki/Porsche_Boxsterhttp://en.wikipedia.org/wiki/Subaru_XThttp://en.wikipedia.org/wiki/Subaru_SVXhttp://en.wikipedia.org/wiki/Toyota_Camryhttp://en.wikipedia.org/wiki/Toyota_Avalonhttp://en.wikipedia.org/wiki/Toyota_Priushttp://en.wikipedia.org/wiki/Chevrolet_Corvette_C6http://en.wikipedia.org/wiki/Citro%C3%ABn_XMhttp://en.wikipedia.org/wiki/Citro%C3%ABn_C4http://en.wikipedia.org/wiki/Lexus_IShttp://en.wikipedia.org/wiki/Mitsubishi_Diamante

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0.28Porsche 997 Carrera(with optional automatic spoiler, PDK transmission 0.30)

2004

0.28 Renault 25 TS 1984

0.28 Rumpler-Tropfenwagen 1921

0.28 Saab 9-3 2003

0.28 Toyota Camry / Lexus ES 2001

0.28 Volkswagen NewBeetle with custom, hand-crafted wing[7] 2003

0.28 Opel Astra Coupe Turbo 2003

0.27 Honda Civic Hybrid 2006

0.27 Hyundai Genesis 2009

0.27Infiniti G35(0.26 with "aero package")

2002

0.27 Lexus GS 2005

0.27 Mazda6(sedan and hatchback) [8] 2008

0.27 Mercedes-Benz W203 C-Class Sedan 2001

0.27 Nissan GT-R 2008

0.27 Toyota Camry Hybrid 2007

0.27 Tucker Torpedo 1948

0.27 Volkswagen Passat B5 (sedan) 1997

0.27Mercedes-Benz S Class(0.268 with Sport Package)

2000-2005

0.26 Hotchkiss Gregoire[citation needed] 1951

0.26Lexus LS 430(0.25 with air suspension)

2001-2006

0.26 Lexus LS 460 20060.26 Mercedes-Benz W221 S-Class 2006

0.26Opel Calibra(8 valve version)

1989

0.26 Toyota Prius 2004-2009

0.25 Audi A21.2 TDI 2001

0.25 Honda Insight 1999, 2003, 2005

0.25 Toyota Prius 2010

0.24Mercedes E-class coupe(0.25 sedan)

2009

0.212 Tatra T77 19350.195 General Motors EV1 1996

http://en.wikipedia.org/wiki/Porsche_997http://en.wikipedia.org/wiki/Porsche_997http://en.wikipedia.org/wiki/Renault_25http://en.wikipedia.org/wiki/Rumplerhttp://en.wikipedia.org/wiki/Saab_9-3http://en.wikipedia.org/wiki/Toyota_Camryhttp://en.wikipedia.org/wiki/Lexus_EShttp://en.wikipedia.org/wiki/Volkswagen_NewBeetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-6%23cite_note-6http://en.wikipedia.org/w/index.php?title=Opel_Astra_Coupe_Turbo&action=edit&redlink=1http://en.wikipedia.org/wiki/Honda_Civic_Hybridhttp://en.wikipedia.org/wiki/Hyundai_Genesishttp://en.wikipedia.org/wiki/Infiniti_G35http://en.wikipedia.org/wiki/Lexus_GShttp://en.wikipedia.org/wiki/Mazda_6#Second_generation_.282007.E2.80.93.29http://en.wikipedia.org/wiki/Mazda_6#Second_generation_.282007.E2.80.93.29http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Mercedes-Benz_C-Classhttp://en.wikipedia.org/wiki/Nissan_GT-Rhttp://en.wikipedia.org/wiki/Toyota_Camry_Hybridhttp://en.wikipedia.org/wiki/1948_Tucker_Sedanhttp://en.wikipedia.org/wiki/Volkswagen_Passat#Passat_Mk5_.28B5.2FB5.5.2FLingyu.2C_1996.E2.80.932005.2FPresent:_Shangai_Volkswagen.29http://en.wikipedia.org/wiki/Mercedes-Benz_W220http://en.wikipedia.org/wiki/Hotchkiss_et_Ciehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Lexus_LS_430http://en.wikipedia.org/wiki/Lexus_LS_460http://en.wikipedia.org/wiki/Mercedes-Benz_W221http://en.wikipedia.org/wiki/Opel_Calibrahttp://en.wikipedia.org/wiki/Toyota_Priushttp://en.wikipedia.org/wiki/Audi_A2http://en.wikipedia.org/wiki/Audi_A2http://en.wikipedia.org/wiki/Honda_Insighthttp://en.wikipedia.org/wiki/Toyota_Priushttp://en.wikipedia.org/wiki/Mercedes_E-classhttp://en.wikipedia.org/wiki/Tatra_T77http://en.wikipedia.org/wiki/General_Motors_EV1http://en.wikipedia.org/wiki/Porsche_997http://en.wikipedia.org/wiki/Porsche_997http://en.wikipedia.org/wiki/Renault_25http://en.wikipedia.org/wiki/Rumplerhttp://en.wikipedia.org/wiki/Saab_9-3http://en.wikipedia.org/wiki/Toyota_Camryhttp://en.wikipedia.org/wiki/Lexus_EShttp://en.wikipedia.org/wiki/Volkswagen_NewBeetlehttp://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-6%23cite_note-6http://en.wikipedia.org/w/index.php?title=Opel_Astra_Coupe_Turbo&action=edit&redlink=1http://en.wikipedia.org/wiki/Honda_Civic_Hybridhttp://en.wikipedia.org/wiki/Hyundai_Genesishttp://en.wikipedia.org/wiki/Infiniti_G35http://en.wikipedia.org/wiki/Lexus_GShttp://en.wikipedia.org/wiki/Mazda_6#Second_generation_.282007.E2.80.93.29http://en.wikipedia.org/wiki/Automobile_drag_coefficient#cite_note-7%23cite_note-7http://en.wikipedia.org/wiki/Mercedes-Benz_C-Classhttp://en.wikipedia.org/wiki/Nissan_GT-Rhttp://en.wikipedia.org/wiki/Toyota_Camry_Hybridhttp://en.wikipedia.org/wiki/1948_Tucker_Sedanhttp://en.wikipedia.org/wiki/Volkswagen_Passat#Passat_Mk5_.28B5.2FB5.5.2FLingyu.2C_1996.E2.80.932005.2FPresent:_Shangai_Volkswagen.29http://en.wikipedia.org/wiki/Mercedes-Benz_W220http://en.wikipedia.org/wiki/Hotchkiss_et_Ciehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Lexus_LS_430http://en.wikipedia.org/wiki/Lexus_LS_460http://en.wikipedia.org/wiki/Mercedes-Benz_W221http://en.wikipedia.org/wiki/Opel_Calibrahttp://en.wikipedia.org/wiki/Toyota_Priushttp://en.wikipedia.org/wiki/Audi_A2http://en.wikipedia.org/wiki/Honda_Insighthttp://en.wikipedia.org/wiki/Toyota_Priushttp://en.wikipedia.org/wiki/Mercedes_E-classhttp://en.wikipedia.org/wiki/Tatra_T77http://en.wikipedia.org/wiki/General_Motors_EV1

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UNIT 3:

Windshield angle:

Recall the aerodynamic data presented in Chapter 2, Fig. 2.22, on two basic ellipsoid

shapes with dimensions reminiscent of the ratios used on road vehicles. The importantconclusion to be drawn from this Figure is that both positive and negative lift can be

generated by bodies when placed close to the ground. Drag, however, is primarily a result

of the blunt rear-end shape, which creates local flow separation, as shown in Fig. 2.3

(note that skin-friction drag is usually small, as indicated in Table 2.4). While the first

type of design in Fig. 2.22 will focus on highly streamlined shapes, with minimum rear-

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end flow separations, flow separations may appear in different locations on vehicles with

more angular geometries, and vortex dominated flows can exist on a variety of road

vehicles. In order to reintroduce this concept of vortex-dominated flows, let us return to

the discussion of a flat-plate lifting surface (described in Chapter 3, and shown again in

Fig. 6.4). In this case, a thin, low-aspect-ratio flat plate is placed in a free stream at an

angle of attack larger than 10. The main aspect of this flow field, relevant to the present

discussion, is the formation of two concentrated side edge vortices which dominate the

nearby flow field. Those two vortices induce a large velocity on the plate (under the

vortices), creating strong suction forces which considerably increase the lift of the flat-

plate wing.

Interestingly, a similar situation develops when slanting the rear, upper surface of a

generic body (Fig. 6.4B). This vortex-dominated flow is present in a slant-angle range of

10< ? < 30, as indicated by the lift and drag data in Fig. 6.5 (region I). At larger angles

? , the flow over the whole rear base area is separated, as on a typical bluff body.

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This fully separated case is indicated as region II, and Fig. 6.5B shows that the

corresponding pressure distribution (along a lateral line AA) is evenly distributed. In

region I, the two concentrated side vortices attach the flow near the bodys longitudinal

centerline (Fig. 6.5C), effectively creating a lifting flow. The pressure distribution for this

case shows the large negative pressure peaks created by the vortices at the side of the

slanted rear surface (Fig. 6.5B, region I) resulting in a force acting normal to the slanted

surface (which can be resolved into lift and drag).

As the slant angle is increased from zero, a positive lift will develop, which increases up

to ? = 30. At slant angles larger than 10 the rearward projection of this negative

pressure causes quite a large increase in drag, as shown in this Figure. The most

interesting feature of this data is that above a critical angle (close to ? = 30) the vortex

structure breaks down and the drag and lift contribution of the slanted surface is much

smaller. This fact has an effect on hatchback automobile design, where rear window

inclination angle should be more than 35 or less than, say, 25. Also, note that in this

case, the basic body (with ? = 0) has negative lift due to ground effect, similar to the

case with the ellipsoid, shown in Fig. 2.22.

Another typical pattern of flow-separation frequently found on three-box-type sedans isdepicted in Fig. 6.4C. In this case a separated bubble, with locally recirculating flow, is

observed in the front, at the break point between the bonnet and the windshield. The large

angle created between the rear windshield and trunk area results in a second, similar

flow-

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recirculation area. Data on the effect of those parameters on the drag can be found in Ref.

2.6, Chapter 5.

When inverting the body so that now the lower surface of the body is slanted (Fig. 6.4D),

a similar trend can be expected. This principle can be utilized for race cars since for

moderate angles (usually less than ? = 15) an increase in the downforce is observed (see

also Ref. 2.6, pp. 143-144). However, a far more interesting case is when two side plates

are added to create an underbody tunnel, sometimes called venturi (Fig. 6.4E). This

geometry can generate very large values of negative lift, with only a moderate increase in

drag, as shown in Fig. 6.6 (after Ref. 6.2). Furthermore, the downforce created by this

geometry increases with smaller ground clearances (and probably larger values can be f

ined by adding skirts along the sides of this particular body).

Car Oriented Basic Aerodynamic Shapes

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The previous section dealt with some aerodynamic features of boxy shapes in ground

proximity, whereas in this section the target is to present basic body shapes that can

create downforce without creating large drag force. With these earlier basic shapes in

mind it is possible to define a limited number of conceptual race car configurations, and

some are presented

The first generic shape in Fig.

6.7A is aimed at a very low-drag

configuration, and such

configurations were studied

by Morelli, in Ref. 2.4, pp. 70-98.

The basic intention is to create a

vehicle body with very low drag,

and at the same time to be able

to generate lift or downforce

with the body. The above cited

article indicates that with suchconfigurations, drag

coefficient values of less than C

D = 0.1 are obtainable,

while lift can be varied by

slightly pitching the body. The

lift coefficient can range from CL

= 0.25 at a positive pitch of 6,

down to about C L = -0.75 for a

negative pitch of 6. Such low-drag configurations are usually applicable to speed-record

cars that run along long straightaways, without any turns. Such vehicles usually require

low levels of downforce, primarily to improve their high-speed stability, and usually do

not have additional lifting surfaces (wings). An example is presented in Fig. 6.8, the

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Oldsmobile Aerotech Aurora V-8, which broke 47 speed-endurance records in December

1992.

On most

racing circuits with medium- to high-speed turns, vehicles with high downforce can run

faster lap times (see Chapter 5). If an aerodynamicist is asked to recommend a

configuration for such a circuit with high downforce and relatively low drag, then very

likely his choice will be based on an inverted wing in ground effect, as shown in Fig.

6.7B. (Recall the large increase in the lift or downforce of a wing when placed near the

ground--ground effect.) The addition of side fins to seal the airflow from the sides

considerably increases the downforce (since the lift of a two-dimensional airfoil is larger

than that of a low-span wing).

Applications of this principle were incorporated into the "skirt era" race cars, and an

example is shown in Fig. 6.9. In this Lotus 79 F-1 car the lower surface of the side pods

resembled an inverted airfoil, while the side skirts (sliding on the road) effectively

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created the high downforce (more information on this important concept is presented later

in this chapter and in Chapter 7).

A more realistic shape that can be related to prototype race cars is the "catamaran"

concept (Fig. 6.7C.) The need to cover the wheels at the two sides of the vehicle resulted

in a shape with a fairly high central tunnel ending with a moderate upward, rear slope

(venturi). The ability to channel the momentum of the undisturbed free stream under the

car reduces the area of flow separation on the back of the central body, creating an ideal

high-downforce and low-drag configuration. Some modern prototype race cars are

partially utilizing this principle. As an example, a generic model for such a vehicle is

depicted in Fig. 6.10, with which L/D values of over 6 were obtained.

A far more popular concept is the "vacuum cleaner" car (Fig. 6.7D). In this case every

effort is made to seal the gap between the front and the two sides of the vehicle and the

ground, to minimize or entirely eliminate any airflow there. Because of the flow

separation at the base, the base pressurepb is very low, and by leaving the rear section of

the car open so that this pressure prevails under the car, a strong suction force

(downforce) is created. The suction force can be increased by a small spoiler, and the

lift/drag ratio (due to this pressure) can be fairly well approximated by the length/height

ratio (e.g.,L/D ~L/h ). A logical improvement on this concept is the addition of a fan that

on one hand creates vacuum under the car, and on the other hand blows the air out at the

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base,

the

separated flow bubble behind the car and reducing drag.

This idea was discovered very early, and the Chaparral 2J, shown in Fig. 6.11, was the

first race car to utilize this principle. The success of this concept led quickly to the

banning of active aerodynamic devices, such as fans or variable

angle wings, on race cars. The remaining alternative is to reduce the base pressure by

using a wing, while at the same time reducing the height of the rear bodyworkh for drag-

saving considerations. The prototype race car shown in Fig. 6.12 can be used as an

example for this design philosophy; however, the high rear deck in this case probably

resulted in an undesirable increase in drag.

The principle of vortex lift (see Chapter 3) on slender wings can also be used to createdownforce. In the particular case depicted in Fig. 6.7E, the inverted delta wing shown can

create downforce on the order ofCL ~ -1.3 (based on wing surface area) at a negative

pitch of about 30, with a downforce/drag ratio of about 1.7. This principle was tested on

a generic open-wheel race car, shown in Fig. 6.13, where the drag of the open wheels

reduced the downforce/drag ratio to about 1. One of the disadvantages of this concept is

that the side edge vortex-wake of the delta planform considerably reduces the

effectiveness of a conventional rear wing when placed behind it, so when using a rear

wing, the main delta-wing plane must be set at a much smaller angle of attack. Of course,

numerous applications of this principle can be seen in the form of the small dive plates (at

an angle of attack) which are attached to the nose or aft sections of many race cars (as

shown later).

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AERODYNAMICS OF THE COMPLETE VEHICLE

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In the preceding section the influence of the vehicle shape on aerodynamics was

investigated; in this section it is assumed that the vehicle geometry has already been

fixed. The typical parameters affecting the aerodynamic performance of existing vehicles

are usually side-slip angle, bodys incidence, and ride height. The effect of these

parameters on vehicle aerodynamics will be demonstrated on two types of vehicles: a

sports sedan and an open-wheel race car. The aerodynamic coefficients depend strongly

on a vehicles shape, and can change considerably from one configuration to another.

Therefore, the following two examples demonstrate the generic trends, but are not

necessarily accurate for any particular vehicle.

For the first example, let us examine a generic sports sedan. Its top view is shown in Fig.

6.14 (this data is for a 20% scale model, at Re L = 3.0 x 106 , with smooth underbody).

The graph depicts the effect of wind side-slip angle Won the aerodynamic coefficients.

In order to explain the source of these aerodynamic loads let us observe the generic flow

field depicted in Fig. 6.15. Basically, for the small, near-zero side-slip conditions the flow

is attached on the vehicles sides, and the pressure distribution (from a top view)

resembles the pressure distribution on a thick airfoil.

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The pressure distribution data of Fig. 6.16 (after SAE paper 73-0232) reinforces this

compa