Automotive aerodynamics - AbsoluteAstronomy.com

Automotive aerodynamics is the study of the aerodynamics

Aerodynamics

Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...

of road vehicles. The main concerns of automotive aerodynamics are reducing drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

(though drag by wide wheels is dominating most cars), reducing wind noise, minimizing noise emission

Roadway noise

Roadway noise is the collective sound energy emanating from motor vehicles. In the USA it contributes more to environmental noise exposure than any other noise source, and is constituted chiefly of engine, tire, aerodynamic and braking elements...

, and preventing undesired lift

Lift (force)

A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

forces and other causes of aerodynamic instability 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

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

arcs and lights into the overall shape to reduce drag. It will be streamlined

Streamliner

A streamliner is a vehicle incorporating streamlining in a shape providing reduced air resistance. The term is applied to high-speed railway trainsets of the 1930s to 1950s, and to their successor "bullet trains". Less commonly, the term is applied to fully faired recumbent bicycles...

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

Windshield

The windshield or windscreen of an aircraft, car, bus, motorbike or tram is the front window. Modern windshields are generally made of laminated safety glass, a type of treated glass, which consists of two curved sheets of glass with a plastic layer laminated between them for safety, and are glued...

and will feature a sort of tail called a fastback

Fastback

A fastback is a car body style whose roofline slopes continuously down at the back. The word can also designate the car itself. The style is seen on two-door coupés as well as four-door sedans.-History:...

or Kammback

Kammback

A Kammback is a car body style that derives from the research of the German aerodynamicist Wunibald Kamm in the 1930s. The design calls for a body with smooth contours that continues to a tail that is abruptly cut off. This shape reduces the drag of the vehicle."Kammback" is an American term...

or liftback.
Note that the Aptera 2e, the Loremo

Loremo

Loremo AG is a German automaker corporation, based in Marl. It was founded in 2000. Loremo is focused on designing prototypes of cars with very low weight and air resistance, the term "Loremo" is an abbreviation for "Low Resistance Mobile". Initially the car was conceived for emerging markets...

, and the Volkswagen 1-litre car

Volkswagen 1-litre car

The Volkswagen 1-litre car is a two-person diesel concept car produced by Volkswagen. The 1-litre car was designed to be able to travel 100 km on 1 litre of diesel fuel, , while being both roadworthy and practical...

try to reduce the area of their back.
It will have a flat and smooth floor to support the Venturi effect

Venturi effect

The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is named after Giovanni Battista Venturi , an Italian physicist.-Background:...

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

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

, and for passengers, then reaccelerated by a nozzle

Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....

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

Slipstream

A slipstream is a region behind a moving object in which a wake of fluid is moving at velocities comparable to the moving object . The term slipstream also applies to the similar region adjacent to an object with a fluid moving around it...

. 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

Suspension (vehicle)

Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...

is either streamlined (Aptera) or retracted.
Door handle

Door handle

A door handle is an attached mechanism used to open or close a door. In the United States, door handle can refer to any fixed or lever-operated door latch device, including on car doors. The term door knob tends to refer to round operating mechanisms.-History:The first documented invention of the...

s, the antenna, and roof rails can have a streamlined shape. The side mirror can only have a round fairing as a nose.
Air flow through the wheel-bays is said to increase drag (German source) though race cars need it for brake cooling and a lot of cars emit the air from the radiator into the wheel bay.

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

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

varies as the square of speed). Fourth, a ground vehicle has fewer degrees of freedom

Degrees of freedom (physics and chemistry)

A degree of freedom is an independent physical parameter, often called a dimension, in the formal description of the state of a physical system...

than an aircraft, and its motion is less affected by aerodynamic forces. Fifth, 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. Roads are also much worse (smoothness, debris) than the average airstrip. Lastly, car drivers are vastly under-trained compared to pilots, and usually will not drive to maximize efficiency.

Automotive aerodynamics is studied using both computer modelling

Computational fluid dynamics

Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with...

and wind tunnel

Wind tunnel

A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...

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

Boundary layer

In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...

forming on the floor of the working section and affecting the results. An example of such a rolling road wind tunnel is Wind Shear's Full Scale, Rolling Road, Automotive Wind Tunnel

Wind Shear's Full Scale, Rolling Road, Automotive Wind Tunnel

In January 2008 Wind Shear, a division of US machine tool builder Haas Automation, completed construction on one of the most advanced automotive wind tunnels in the world. The full scale tunnel is located adjacent to Concord Regional Airport in Concord, North Carolina...

built in 2008 in Concord, North Carolina.

Drag coefficient

In fluid dynamics, the drag coefficient 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 equation, where a lower drag coefficient indicates the object will have less aerodynamic or...

(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 Homepage.

Some examples:

Drag area ( C_d x Ft²)	Year Automobile
3.95	1996 GM EV1 General Motors EV1 The General Motors EV1 was an electric car produced and leased by the General Motors Corporation from 1996 to 1999. It was the first mass-produced and purpose-designed electric vehicle of the modern era from a major automaker, and the first GM car designed to be an electric vehicle from the...
5.10	1999 Honda Insight Honda Insight The Honda Insight is a hybrid electric vehicle manufactured by Honda and the first production vehicle to feature Honda's Integrated Motor Assist system. The first-generation Insight was produced from 1999 to 2006 as a three-door hatchback...
5.40	1989 Opel Calibra Opel Calibra The Opel Calibra, also known as the Vauxhall Calibra in the United Kingdom, the Chevrolet Calibra in South America, and the Holden Calibra in Australia and New Zealand is a sports car engineered and produced by German automaker Opel between 1989 and 1997, but sold until 1999 in the UK...
5.54	1980 Ferrari 308 GTB Ferrari 308 GTB The Ferrari 308 GTB are mid-engined sports cars manufactured by the Italian company Ferrari in the 1970s-1980s. They made up the lower end of the company's range...
5.61	1993 Mazda RX-7 Mazda RX-7 Series 1 is commonly referred to as the "SA22C" from the first alphanumerics of the vehicle identification number. This series of RX-7 had exposed steel bumpers and a high-mounted indentation-located license plate, called by Werner Buhrer of Road & Track magazine a "Baroque depression."In 1980...
5.61	1993 McLaren F1 McLaren F1 The McLaren F1 is a supercar designed and manufactured by McLaren Automotive. Originally a concept conceived by Gordon Murray, he convinced Ron Dennis to back the project and engaged Peter Stevens to design the exterior of the car...
5.63	1991 Opel Calibra Opel Calibra The Opel Calibra, also known as the Vauxhall Calibra in the United Kingdom, the Chevrolet Calibra in South America, and the Holden Calibra in Australia and New Zealand is a sports car engineered and produced by German automaker Opel between 1989 and 1997, but sold until 1999 in the UK...
5.64	1990 Bugatti EB110 Bugatti EB110 The Bugatti EB110 is a mid-engine sports car from Bugatti Automobili SpA. It was unveiled on September 15, 1991, in both Versailles and in front of the Grande Arche at La Défense in Paris, France, exactly 110 years after Ettore Bugatti's birth....
5.71	1990 Honda CRX
5.74	2002 Acura NSX
5.76	1968 Toyota 2000GT Toyota 2000GT The Toyota 2000GT is a limited-production, front-engine, rear-wheel drive, two-seat, hardtop coupé grand tourer designed by Toyota in collaboration with Yamaha. First displayed to the public at the Tokyo Motor Show in 1965, the 2000GT was manufactured under contract by Yamaha between 1967 and...
5.88	1990 Nissan 240SX Nissan 240SX The 240SX is a two-door compact car that was introduced to the North American market by Nissan in 1988 for the following model year. It replaced the outgoing 200SX model. Most of the 240SX were equipped with the 2.4-liter inline 4 engine . The KA24E being single over-head cam and KA24DE being dual...
5.86	2001 Audi A2 1.2 TDI 3L Audi A2 The Audi A2 is a Compact MPV styled five-door four- or five-seat hatchback designed supermini, produced by the German automaker Audi AG from November 1999 to 2005...
5.92	1994 Porsche 911 Porsche 911 The Porsche 911 is a luxury 2-door sports coupe made by Porsche AG of Stuttgart, Germany. It has a distinctive design, rear-engined and with independent rear suspension, an evolution of the swing axle on the Porsche 356. The engine was also air-cooled until the introduction of the Type 996 in 1998... Speedster
5.95	1994 McLaren F1 McLaren F1 The McLaren F1 is a supercar designed and manufactured by McLaren Automotive. Originally a concept conceived by Gordon Murray, he convinced Ron Dennis to back the project and engaged Peter Stevens to design the exterior of the car...
6.00	1970 Lamborghini Miura Lamborghini Miura The Lamborghini Miura was a sports car produced by Italian automaker Lamborghini between 1966 and 1972. The car is widely considered to have begun the trend of high performance, two-seater, mid-engined sports cars... S
6.00	1992 Subaru SVX
6.06	2003 Opel Astra Coupe Turbo
6.08	2008 Nissan GTR
6.13	1991 Acura NSX
6.15	1989 Suzuki Swift GT
6.17	1995 Lamborghini Diablo Lamborghini Diablo The Lamborghini Diablo is a high-performance mid-engined sports car that was built by Italian automaker Lamborghini between 1990 and 2001. It was the first Lamborghini capable of attaining a top speed in excess of . After the end of its production run in 2001, the Diablo was replaced by the...
6.24	2004 Toyota Prius Toyota Prius The Toyota Prius is a full hybrid electric mid-size hatchback, formerly a compact sedan developed and manufactured by the Toyota Motor Corporation...
6.27	1986 Porsche 911 Carrera
6.27	1992 Chevrolet Corvette Chevrolet Corvette The Chevrolet Corvette is a sports car by the Chevrolet division of General Motors that has been produced in six generations. The first model, a convertible, was designed by Harley Earl and introduced at the GM Motorama in 1953 as a concept show car. Myron Scott is credited for naming the car after...
6.35	1999 Lotus Elise Lotus Elise The 1996 Lotus Elise weighed . Because of its relatively low weight, it was able to accelerate 0- in 5.8 seconds despite its relatively low power output of...
6.77	1995 BMW M3 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. M3 models have been derived from the E30, E36, E46 and E90/E92/E93 3-series, and sold with coupé, sedan and convertible body styles...
6.79	1993 Corolla DX Toyota Corolla The Toyota Corolla is a line of subcompact and compact cars manufactured by the Japanese automaker Toyota, which has become very popular throughout the world since the nameplate was first introduced in 1966. In 1997, the Corolla became the best selling nameplate in the world, with over 35 million...
6.81	1989 Subaru Legacy Subaru Legacy The Subaru Legacy is a mid-size car built by the Japanese company Fuji Heavy Industries, and manufactured by its division Subaru since 1989, and is available as a sedan or wagon. Part of the original design goals for the Legacy model was to provide Subaru a vehicle in which they could compete in...
6.96	1988 Porsche 944 Porsche 944 The Porsche 944 is a sports car built by Porsche from 1982 to 1991. It was built on the same platform as the 924, although 924 production continued through 1988. The 944 was intended to last into the 1990s, but major revisions planned for a 944 S3 model were eventually rolled into the 968 instead,... S
7.02	1992 BMW 325I
7.10	Saab 900 Saab 900 The Saab 900 was a car produced by Saab Automobile from 1978 until 1998 in two generations. The first generation from 1978 to 1993 is known as the "classic"; the generation from 1994 to 1998 is known as the "new generation" ....
7.13	2007 SSC Ultimate Aero
7.48	1993 Chevrolet Camaro Z28 Chevrolet Camaro The Chevrolet Camaro is an automobile manufactured by General Motors under the Chevrolet brand, classified as a pony car and some versions also as a muscle car. It went on sale on September 29, 1966, for the 1967 model year and was designed as a competing model to the Ford Mustang...
7.57	1992 Toyota Camry Toyota Camry The Toyota Camry is a series of mid-size automobiles manufactured by Toyota since 1982, and sold in the majority of automotive markets throughout the world...
8.70	1990 Volvo 740 Turbo
8.71	1991 Buick LeSabre Buick LeSabre 1959LeSabre and all other 1959 Buicks not only got new names, but all-new styling as well, adopting the new GM B- and C-body used on all of the corporation's full-sized cars... Limited
9.54	1992 Chevy Caprice Wagon
10.7	1992 Chevrolet S-10 Blazer Chevrolet S-10 Blazer The Chevrolet Blazer and the similar GMC S-15 Jimmy are mid-size SUVs from General Motors. Production began alongside the larger K5 Blazer and Jimmy in 1983 and lasted through 2005. In the United States retail sales after 2004 were limited to two-door Blazer models, all other models being sold...
11.63	1991 Jeep Cherokee Jeep Cherokee (XJ) The Jeep Cherokee is a unibody compact SUV. It shared the name of the original full-size SJ model, but without a body-on-frame chassis, it set the stage for the modern SUV. Its innovative appearance and sales popularity spawned important imitators as other automakers began to notice that this...
13.10	1990 Range Rover Classic
13.76	1994 Toyota T100 Toyota T100 The Toyota T100 was a full-sized pickup truck introduced by Toyota in late 1992 as a 1993 calendar year vehicle.... SR5 4x4
14.52	1994 Toyota Land Cruiser Toyota Land Cruiser The is a series of four-wheel drive vehicles produced by the Japanese car maker Toyota Motor Corporation. It is not related to the Studebaker Land Cruiser car produced in the US from 1934-1954....
17.43	1992 Land Rover Discovery Land Rover Discovery The Discovery was introduced into the United Kingdom in 1989. The company code-named the vehicle "Project Jay". The new model was based on the chassis and drivetrain of the more upmarket Range Rover, but with a lower price aimed at a larger market segment and intended to compete with Japanese...
18.03	1992 Land Rover Defender 90
18.06	1993 Hummer H1 Hummer H1 The Hummer H1 is a civilian off-road vehicle based on the M998 Humvee, which was created by AM General. The vehicle was produced from 1992 through 2006, and was the first of what became the Hummer line...
20.24	1993 Land Rover Defender 110
26.32	2006 Hummer H2 Hummer H2 The Hummer H2 is an SUV and SUT that was marketed by General Motors under the Hummer brand. It is a large truck , while longer, heavier , and taller with room for six passengers , seven passengers in some models. The rearmost part of the H2 SUV was modified to a pickup truck bed for the 2005 H2 SUT...

Relationship to velocity

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.

Downforce

Downforce is a downwards thrust created by the aerodynamic characteristics of a car. The purpose of downforce is to allow a car to travel faster through a corner by increasing the vertical force on the tires, thus creating more grip....

describes the downward pressure created by the aerodynamic

Aerodynamics

characteristics of a car

Čar

Čar is a village in the municipality of Bujanovac, Serbia. According to the 2002 census, the town has a population of 296 people.-References:...

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.

Drag coefficient

Relationship to velocity

Downforce

See also