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Information about Automotive Aerodynamics

Automotive aerodynamics is the study of the aerodynamics of road vehicles. The main concerns of automotive aerodynamics are reducing drag, reducing wind noise, mimimising noise emission and preventing undesired lift forces at high speeds. For some classes of racing vehicles, it may also be important to produce desirable downwards aerodynamic forces to improve traction and thus cornering abilities.

An aerodynamic automobile will integrate the wheel and lights in its shape to have a small surface. It will be streamlined, for example it does not have sharp edges crossing the wind stream above the windshield and will feature a sort of tail called a fastback or Kammback or liftback. It will have a flat and smooth floor to support the Venturi effect and produce desirable downwards aerodynamic forces. The air rams into the engine bay, is used (cooling, combustion, and for passengers), reaccelerated by a nozzle and then ejected under the floor.

Automotive aerodynamics differs from aircraft aerodynamics in several ways. First, the characteristic shape of a road vehicle is bluff , compared to an aircraft. Second, the vehicle operates very close to the ground, rather than in free air. Third, the operating speeds are lower. Fourth, the ground vehicle has fewer degrees of freedom than the aircraft, and its motion is less affected by aerodynamic forces.

Automotive aerodynamics is studied using both computer modelling and wind tunnel testing. For the most accurate results from a wind tunnel test, the tunnel is sometimes equipped with a rolling road. This is a movable floor for the working section, which moves at the same speed as the air flow. This prevents a boundary layer forming on the floor of the working section and affecting the results.

Drag coefficient ( Cd) is a commonly published rating of a car's aerodynamic smoothness, related to the shape of the car. Multiplying Cd by the car's frontal area gives an index of total drag. The result is called drag area, and is listed below for several cars. The width and height of curvy cars lead to gross overestimation of frontal area. These numbers use the manufacturer's frontal area specifications from <http://www.mayfco.com/tbls.htm>

Some examples:

Drag area ( Cd x Ft2)

Relationship to velocity

It is well known that the frictional force of aerodynamic drag increases significantly with vehicle speed.[1] As early as the 1920s engineers began to consider automobile shape in reducing aerodynamic drag at higher speeds. By the 1950s German and British automotive engieneers were systematically analysing the effects of automotive drag for the higher performance vehicles.[2] By the late 1960s scientists also became aware of the significant increase in sound levels emitted by automobiles at high speed. These effects were understood to increase the intensity of sound levels for adjacent land uses at a non-linear rate.[3] Soon highway engineers began to design roadways to consider the speed effects of aerodynamic drag produced sound levels, and automobile manufacturers considered the same factors in vehicle design.

See also

References

1. ^ [1]Tuncer Cebeci, Jian P. Shao, Fassi Kafyeke, Eric Laurendeau, Computational Fluid Dynamics for Engineers: From Panel to Navier-Stokes, Springer, 2005, ISBN 3540244514
2. ^ Proceedings: Institution of Mechanical Engineers (Great Britain). Automobile Division: Institution of Mechanical Engineers, Great Britain (1957)
3. ^ C. Michael Hogan & Gary L. Latshaw, The relationship between highway planning and urban noise, Proceedings of the ASCE, Urban Transportation Division specialty conference, May 21/23, 1973, Chicago, Illinois. by American Society of Civil Engineers. Urban Transportation Division
For the Daft Punk song, see .


Aerodynamics (shaping of objects that affect the flow of air or gas) is a branch of fluid dynamics concerned with the study of forces generated on a body in a flow.
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drag (sometimes called resistance) is the force that resists the movement of a solid object through a fluid (a liquid or gas). Drag is made up of friction forces, which act in a direction parallel to the object's surface (primarily along its sides, as friction forces at the
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Roadway noise is the collective sound energy emanating from motor vehicles. In the USA it contributes more to environmental noise exposure[1] than any other noise source, and is constituted chiefly of engine, tire, aerodynamic and braking elements.
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The lift force, lifting force or simply lift is a mechanical force generated by solid objects as they move through a fluid.[1]

While many types of objects can generate lift, the most common and familiar object in this category is the airfoil, a
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A streamliner is any vehicle that incorporates streamlining to produce a shape that provides less resistance to air. The term is usually applied to trains, mostly the high-speed trainsets designed in the United States in the 1930s, 1940s and 1950s, as well as successor "bullet
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windshield (also known as the windscreen) of an aircraft, automobile, bus, motorcycle, or tram is the front window. Modern windshields are generally made of laminated safety glass, which consists of two (typically) curved sheets of glass with a plastic layer laminated
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Fastback. Fiat 127 first series.]]

A fastback is a car body style characterised by a continuous slope from the roof to the base of the decklid. Fastbacks can be two-door coupés or two- or four-door sedans.
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Kammback (or Kamm-tail) is a car body style influenced by the research of the German aerodynamicist Wunibald Kamm in the 1930s.

Aerodynamics

Kamm showed that a better drag-reducing tail end design for a car is one that tapers and is then cut off abruptly.
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liftback is a car body style in which the cargo space (trunk or boot) is accessed through a tailgate that extends up to the higher end of the C-pillar and includes the rear window.
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Venturi effect is an example of Bernoulli's principle, in the case of incompressible fluid flow through a tube or pipe with a constriction in it. The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to
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Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames.
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A nozzle is a mechanical device designed to control the characteristics of a fluid flow as it exits (or enters) an enclosed chamber or pipe.

A nozzle is often a pipe or tube of varying cross sectional area, and it can be used to direct or modify the flow of a fluid (liquid
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Degrees of freedom is a general term used in explaining dependence on parameters, and implying the possibility of counting the number of those parameters.

Degrees of freedom in mechanics (physics)


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Computational fluid dynamics (CFD) is one of the branches of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows.
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wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects.

Ways that wind-speed and flow are measured in wind tunnels:

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In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface. In the Earth's atmosphere the planetary boundary layer is the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the
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The drag coefficient (Cd, Cx or Cw, depending on the country) is a dimensionless quantity that describes a characteristic amount of aerodynamic drag caused by fluid flow, used in the drag equation.
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Gasoline: 1.5 L DOHC I4
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102 N·m (75 ft·lbf) @ 4000 rpm
Electric: 288 V motor
30 kW (40 hp) @ 940 rpm
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E30 M3



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