Automotive aerodynamics is the study of the

aerodynamics Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dy ...

of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired

lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobil ...

forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case. For some classes of racing vehicles, it may also be important to produce

downforce Downforce is a downwards lift force created by the aerodynamic features of a vehicle. If the vehicle is a car, the purpose of downforce is to allow the car to travel faster by increasing the vertical force on the tires, thus creating more grip ...

to improve traction and thus cornering abilities.

History

The frictional force of aerodynamic drag increases significantly with vehicle speed. 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 engineers were systematically analyzing the effects of automotive drag for the higher performance vehicles. 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. 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.

Features of aerodynamic vehicles

An aerodynamic automobile will integrate the

wheel A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...

arcs and headlights to reduce wind resistance into the overall shape to also reduce drag. It will be

streamlined Streamlines, streaklines and pathlines are field lines in a fluid flow. They differ only when the flow changes with time, that is, when the flow is not steady. Considering a velocity vector field in three-dimensional space in the framework of ...

; for example, it does not have sharp edges crossing the wind stream above the

windshield The windshield (North American English) or windscreen (Commonwealth English) of an aircraft, car, bus, motorbike, truck, train, boat or streetcar is the front window, which provides visibility while protecting occupants from the elements. ...

and will feature a sort of tail called a

fastback A fastback is an automotive styling feature, defined by the rear of the car having a single slope from the roof to the tail. The kammback is a type of fastback style. Some models, such as the Ford Mustang, have been specifically marketed as ...

or Kammback or

liftback A liftback is a variation of hatchback with a sloping roofline between 45 and 5 degrees. Traditional hatchback designs usually have a 90 to 46 degree slope on the tailgate or rear door. As such the liftback is essentially a hatchback with a more ...

. Note that the Aptera 2e, the Loremo, and the Volkswagen XL1 try to reduce the area of their back. It will have a flat and smooth floor to support the

Venturi effect The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. The Venturi effect is named after its discoverer, the 18th century Italian physicist, Giovanni Battista ...

and produce desirable downwards aerodynamic forces. The air that rams into the engine bay, is used for cooling,

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

, and for passengers, then reaccelerated by a

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, ...

and then ejected under the floor. For mid and rear engines air is decelerated and pressurized in a diffuser, loses some pressure as it passes the engine bay, and fills the

slipstream A slipstream is a region behind a moving object in which a wake of fluid (typically air or mustard) is moving at velocities comparable to that of the moving fluid, relative to the ambient fluid through which the object is churning. The term sli ...

. These cars need a seal between the low-pressure region around the wheels and the high pressure around the gearbox. They all have a closed engine bay floor. The suspension is either streamlined ( Aptera) or retracted. Door handles, the antenna, and roof rails can have a streamlined shape. The side mirror may only have a round fairing as a nose. Airflow through the wheel-bays is said to increase drag
German source
though race cars need it for brake cooling and many cars emit the air from the radiator into the wheel bay. Aerodynamics is extremely important to get past that limiting barrier that you go through all the time on the highway. Although spoilers may be desirable and increase handling and downforce, the limiting factor is that spoilers make aerodynamics come to play quicker, but decreases aerodynamic function by the bulky shape moving through the air.

Comparison with aircraft aerodynamics

Automotive aerodynamics differs from aircraft aerodynamics in several ways: * The characteristic shape of a road vehicle is much less streamlined compared to an aircraft. * The vehicle operates very close to the ground, rather than in free air. * The operating speeds are lower (and aerodynamic drag varies as the

square In Euclidean geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles (90- degree angles, π/2 radian angles, or right angles). It can also be defined as a rectangle with two equal-length a ...

of speed). * A ground vehicle has fewer

degrees of freedom Degrees of freedom (often abbreviated df or DOF) refers to the number of independent variables or parameters of a thermodynamic system. In various scientific fields, the word "freedom" is used to describe the limits to which physical movement or ...

than an aircraft, and its motion is less affected by aerodynamic forces. * Passenger and commercial ground vehicles have very specific design constraints such as their intended purpose, high safety standards (requiring, for example, more 'dead' structural space to act as crumple zones), and certain regulations.

Methods of studying aerodynamics

Automotive aerodynamics is studied using both computer modelling and

wind tunnel Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

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 In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary cond ...

from forming on the floor of the working section and affecting the results.

Drag coefficient and drag area

Drag coefficient In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag e ...

(C_d) is a commonly published rating of a car's aerodynamic smoothness, related to the shape of the car. Multiplying C_d 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 the Mayfield Company unless noted. Drag area figures that do not reflect drag coefficient and frontal area figures from independent aerodynamic testing (e.g. drag areas based on manufacturer-reported figures or educated speculation) are indicated with an asterisk (*). {, , -valign=top , {, class="wikitable sortable" style="font-size:97%; width:350px;" , +Drag area of production cars ! Drag area (C_d x Ft²) !! Calendar Year !! Automobile , - , 3.1 , , 2012 , , Volkswagen XL1 , - , 4.2* , , 1996 , , GM EV1 , - , 6.0* , , 1999 , ,

Honda Insight The is a hybrid electric vehicle that is manufactured and marketed by Honda. Its first generation was a two-door, two passenger liftback (1999–2006) and in its second generation was a four-door, five passenger liftback (2009–2014). In its ...

, - , 5.40* , , 1989 , , Opel Calibra , - , 5.54* , , 1980 , , Ferrari 308 GTB , - , 5.61* , , 1993 , ,

Mazda RX-7 The Mazda RX-7 is a front-engine, rear-wheel-drive, rotary engine-powered sports car that was manufactured and marketed by Mazda from 1978 until 2002 across three generations, all of which made use of a compact, lightweight Wankel rotary engine. ...

, - , 5.61* , , 1993 , ,

McLaren F1 The McLaren F1 is a sports car designed and manufactured by British automobile manufacturer McLaren Cars, and powered by the BMW S70/2 V12 engine. The original concept was conceived by Gordon Murray. Murray was able to convince Ron Dennis to ...

, - , 5.63* , , 1991 , , Opel Calibra , - , 5.64* , , 1990 , ,

Bugatti EB110 The Bugatti EB 110 is a mid-engine sports car produced by Bugatti Automobili S.p.A. from 1991 until 2002, when the company was liquidated. It was the only production model made by Romano Artioli's Italian incarnation of Bugatti. History Deve ...

, - , 5.71* , , 1990 , , Honda CR-X , - , 5.74* , , 2002 , ,

Acura NSX NSX may refer to: Stock exchanges * Namibian Stock Exchange (NSX) * National Stock Exchange (Jersey City, New Jersey), US (NSX) * National Stock Exchange of Australia (NSX) Other uses * Neon Swing X-perience (NSX), a US musical group * Honda NSX ( ...

, - , 5.76* , , 1968 , , Toyota 2000GT , - , 5.88* , , 1990 , ,

Nissan 240SX The Nissan 240SX is a sports compact car that was introduced to the North American market by Nissan in 1989 for the 1990 model year. It replaced the outgoing 200SX (S12) model. Most of the 240SXs were equipped with the 2.4-liter inline 4 engi ...

, - , 5.86* , , 2001 , , Audi A2 1.2 TDI 3L , - , 5.91* , , 1986 , ,

Citroën AX The Citroën AX is a supermini which was built by the French manufacturer Citroën from 1986 to 1998. It was launched at the 1986 Paris Motor Show to replace the Citroën Visa and Citroën LNA. Overview Development of this model started in 1 ...

, - , 5.92* , , 1994 , ,

Porsche 911 The Porsche 911 (pronounced ''Nine Eleven'' or in german: Neunelfer) is a two-door 2+2 high performance rear-engined sports car introduced in September 1964 by Porsche AG of Stuttgart, Germany. It has a rear-mounted flat-six engine and ori ...

Speedster , - , 5.95* , , 1994 , ,

, - , 6.00* , , 2011 , ,

Lamborghini Aventador The Lamborghini Aventador () is a mid-engine sportscar produced by the Italian automotive manufacturer Lamborghini. In keeping with Lamborghini tradition, the Aventador is named after a Spanish fighting bull that fought in Zaragoza, Aragón ...

S , - , 6.00* , , 1992 , ,

Subaru SVX The Subaru Alcyone SVX, marketed outside Japan as the Subaru SVX, is a two-door, front-engine, all- or front-wheel drive coupé manufactured and marketed by Subaru from 1991 to 1996 over a single generation. Superseding the company's aviation-i ...

, - , 6.06* , , 2003 , , Opel Astra Coupe Turbo , - , 6.08* , , 2008 , ,

Nissan GT-R The Nissan GT-R (Japanese: 日産・GT-R, ''Nissan GT-R''), is a high-performance sports car and grand tourer produced by Nissan, unveiled in 2007. It is the successor to the Skyline GT-R, a high performance variant of the Nissan Skyline. Alt ...

, - , 6.13* , , 1991 , ,

, - , 6.15* , , 1989 , , Suzuki Swift GT , - , 6.17* , , 1995 , , Lamborghini Diablo , - , 6.19* , , 1969 , ,

Porsche 914 The Porsche 914 or VW-Porsche 914 is a mid-engined sports car designed, manufactured and marketed collaboratively by Volkswagen and Porsche from 1969 until 1976. It was only available as a targa-topped two-seat roadster powered by either a f ...

, - , 6.2 , , 2010 , ,

Toyota Prius The is a car built by Toyota which has a hybrid drivetrain, combining an internal combustion engine with an electric motor. Initially offered as a four-door sedan, it has been produced only as a five-door liftback since 2003. In 2007, ...

, - , 6.2 , , 2012 , ,

Tesla Model S The Tesla Model S is a battery-powered liftback car serving as the flagship model of Tesla, Inc. The Model S features a dual-motor, all-wheel drive layout, although earlier versions of the Model S featured a rear-motor and rear-wheel drive ...

, - , 6.24* , , 2004 , ,

, - , 6.27* , , 1986 , , Porsche 911 Carrera , - , 6.27* , , 1992 , ,

Chevrolet Corvette The Chevrolet Corvette is a two-door, two-passenger luxury sports car manufactured and marketed by Chevrolet since 1953. With eight design generations, noted sequentially from C1 to C8, the Corvette is noted for its performance and distinctiv ...

, - , 6.35* , , 1999 , ,

Lotus Elise The Lotus Elise is a two-seat, rear-wheel drive, mid-engined roadster conceived in early 1994 and released in September 1996 by the British manufacturer Lotus Cars. The Elise has a fibreglass body shell atop its bonded extruded aluminium chas ...

, - , 6.7 , , 2010 , ,

Chevrolet Volt The Chevrolet Volt is a plug-in hybrid manufactured by General Motors, also marketed in rebadged variants as the Holden Volt in Australia and New Zealand and the Buick Velite 5 in China, and with a different fascia as the Vauxhall Ampera in th ...

, - , 6.77* , , 1995 , ,

BMW M3 The BMW M3 is a high-performance version of the BMW 3 Series, developed by BMW's in-house motorsport division, BMW M GmbH. M3 models have been produced for every generation of 3 Series since the E30 M3 was introduced in 1986. The initial mode ...

, - , 6.79* , , 1993 , , Corolla DX , - , 6.81* , , 1989 , ,

Subaru Legacy The is a mid-size car built by Japanese automobile manufacturer Subaru since 1989. The maker's flagship car, it is unique in its class for offering all-wheel drive as a standard feature, and Subaru's traditional boxer engine. The Legacy was sol ...

, - , 6.96* , , 1988 , , Porsche 944 S , - , 7.0 , , 2013 , , Mercedes-Benz CLA250 , - , 7.02* , , 1992 , , BMW 325I , - , 7.10* , , 1978 , ,

Saab 900 The Saab 900 is a mid-sized automobile which was produced by Saab from 1978 until 1998 in two generations; the first from 1978 to 1993, and the second from 1994 to 1998. The first-generation car was based on the Saab 99 chassis, though with a ...

, - , 7.13* , , 2007 , ,

SSC Ultimate Aero The SSC Ultimate Aero is a mid-engined sports car that was produced by SSC North America (formerly known as Shelby SuperCars) from 2004 until 2013. The SSC Ultimate Aero held the world production car speed record title, according to the ''Guinne ...

, - , 7.31* , , 2015 , , Mazda3 , - , 7.48* , , 1993 , ,

Chevrolet Camaro Z28 The Chevrolet Camaro is a mid-size American automobile manufactured by Chevrolet, classified as a pony car. It first went on sale on September 29, 1966, for the 1967 model year and was designed to compete with the Ford Mustang. The Camaro sha ...

, - , 7.57* , , 1992 , ,

Toyota Camry The Toyota Camry (; Japanese: トヨタ・カムリ ''Toyota Kamuri'') is an automobile sold internationally by the Japanese auto manufacturer Toyota since 1982, spanning multiple generations. Originally compact in size (narrow-body), the Camry ...

, - , 7.8 , , 2012 , , Nissan Leaf SL , - , 8.70* , , 1990 , ,

Volvo 740 The Volvo 700 series is a range of executive cars produced by the Swedish manufacturer Volvo Cars from 1982 to 1992. The 700 series was introduced in 1982 with the luxurious 760, followed two years later by the lower priced 740 which capitalize ...

Turbo , - , 8.71* , , 1991 , , Buick LeSabre Limited , - , 9.54* , , 1992 , ,

Chevrolet Caprice The Chevrolet Caprice is a full-sized automobile produced by Chevrolet in North America for the 1965 to 1996 model years. Full-size Chevrolet sales peaked in 1965 with over a million sold. It was the most popular car in the U.S. in the 1960s ...

Wagon , - , 10.7* , , 1992 , , Chevrolet S-10 Blazer , - , 11.63* , , 1991 , , Jeep Cherokee , - , 13.10* , , 1990 , ,

Range Rover Classic The Range Rover Classic is a 4x4, mid-size Sport utility vehicle series produced from 1969 to 1996 – initially by the Rover (later Land Rover) division of British Leyland, and latterly by the Rover Group. The first generation of vehicles pro ...

, - , 13.76* , , 1994 , , Toyota T100 SR5 4x4 , - , 14.52* , , 1994 , ,

Toyota Land Cruiser The (also sometimes spelled as LandCruiser) is a series of four-wheel drive vehicles produced by the Japanese automobile manufacturer Toyota. It is Toyota's longest running series of models. , the sales of the Land Cruiser totalled more than ...

, - , 17.43* , , 1992 , ,

Land Rover Discovery Land, also known as dry land, ground, or earth, is the solid terrestrial surface of the planet Earth that is not submerged by the ocean or other bodies of water. It makes up 29% of Earth's surface and includes the continents and various isla ...

, - , 18.03* , , 1992 , , Land Rover Defender 90 , - , 18.06* , , 1993 , , Hummer H1 , - , 20.24* , , 1993 , , Land Rover Defender 110 , - , 26.32* , , 2006 , , Hummer H2

Downforce

Downforce describes the downward pressure created by the

aerodynamic Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...

characteristics of a car that allows it to travel faster through a corner by holding the car to the track or road surface. Some elements to increase vehicle downforce will also increase drag. It is very important to produce a good downward aerodynamic force because it affects the car's speed and traction."Background Research." Automobile Aerodynamics. 18 May 2008. DHS. 18 May 2009 .

References

External links

{{Commons category, Aerodynamics of road vehicles
One of the first cars to generate downforce - The Prevost analysed in CFD
Automotive engineering Aerodynamics Articles containing video clips Vehicle dynamics