Aerodynamics ( Ancient Greek : ἀήρ aero (air) + Ancient Greek : 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 dynamics and its subfield of gas dynamics , and is an important domain of study in aeronautics . The term aerodynamics is often used synonymously with gas dynamics, the difference being that "gas dynamics" applies to the study of the motion of all gases, and is not limited to air. The formal study of aerodynamics began in the modern sense in the eighteenth century, although observations of fundamental concepts such as aerodynamic drag were recorded much earlier. Most of the early efforts in aerodynamics were directed toward achieving heavier-than-air flight , which was first demonstrated by Otto Lilienthal in 1891. Since then, the use of aerodynamics through mathematical analysis, empirical approximations, wind tunnel experimentation, and computer simulations has formed a rational basis for the development of heavier-than-air flight and a number of other technologies. Recent work in aerodynamics has focused on issues related to compressible flow , turbulence , and boundary layers and has become increasingly computational in nature.
117-443: A Kammback —also known as a Kamm tail or K-tail —is an automotive styling feature wherein the rear of the car slopes downwards before being abruptly cut off with a vertical or near-vertical surface. A Kammback reduces aerodynamic drag, thus improving efficiency and reducing fuel consumption, while maintaining a practical shape for a vehicle. The Kammback is named after German aerodynamicist Wunibald Kamm for his work developing
234-493: A 2.3-litre five-cylinder petrol engine with an output of 100 kilowatts (136 PS; 134 bhp). The intent was to produce a vehicle which could operate on the engine in the country, and electric mode in the city. Mode of operation could be selected by the driver. Just ten vehicles are believed to have been made; one drawback was that due to the extra weight of the electric drive, the vehicles were less efficient when running on their engines alone than standard Audi 100s with
351-553: A plug to connect to the electrical grid . PHEVs have a much larger all-electric range as compared to conventional gasoline-electric hybrids, and also eliminate the " range anxiety " associated with all-electric vehicles, because the combustion engine works as a backup when the batteries are depleted. In December 2018, Toyota do Brasil announced the development of the world's first commercial hybrid electric car with flex-fuel engine capable of running with electricity and ethanol fuel or gasoline. The flexible fuel hybrid technology
468-426: A shock wave . The presence of shock waves, along with the compressibility effects of high-flow velocity (see Reynolds number ) fluids, is the central difference between the supersonic and subsonic aerodynamics regimes. In aerodynamics, hypersonic speeds are speeds that are highly supersonic. In the 1970s, the term generally came to refer to speeds of Mach 5 (5 times the speed of sound) and above. The hypersonic regime
585-723: A 1.5-liter hybrid system similar to the one used in the Prius c. Sales of the Honda Vezel Hybrid SUV began in Japan began in December 2013. The Range Rover Hybrid diesel-powered electric hybrid was unveiled at the 2013 Frankfurt Motor Show , and retail deliveries in Europe are slated to start in early 2014. Ford Motor Company , the world's second largest manufacturer of hybrids after Toyota Motor Corporation , reached
702-450: A 2.0-litre four-cylinder engine . Research and Development was advancing in the 1990s with projects such as the early BMW 5 Series (E34) CVT hybrid-electric vehicle In 1992, Volvo ECC was developed by Volvo . The Volvo ECC was built on the Volvo 850 platform. In contrast to most production hybrids, which use a gasoline piston engine to provide additional acceleration and to recharge
819-414: A bus, and Koenig-Fachsenfeld patented the idea. Koenig-Fachsenfeld worked with Wunibald Kamm at Stuttgart University, investigating vehicle shapes to "provide a good compromise between everyday utility (e.g. vehicle length and interior dimensions) and an attractive drag coefficient". In addition to aerodynamic efficiency, Kamm emphasized vehicle stability in his design, mathematically and empirically proving
936-443: A car, so automotive designers sought other solutions. In 1935, German aircraft designer Georg Hans Madelung showed alternatives to minimize drag without a long tail. In 1936, a similar theory was applied to cars after Baron Reinhard Koenig-Fachsenfeld developed a smooth roofline shape with an abrupt end at a vertical surface, effective in achieving low amounts of drag similar to a streamlined body. He worked on an aerodynamic design for
1053-482: A continuum. Continuum flow fields are characterized by properties such as flow velocity , pressure , density , and temperature , which may be functions of position and time. These properties may be directly or indirectly measured in aerodynamics experiments or calculated starting with the equations for conservation of mass, momentum , and energy in air flows. Density, flow velocity, and an additional property, viscosity , are used to classify flow fields. Flow velocity
1170-475: A core design concept of most modern production HEVs, was developed in 1967 for the American Motors Amitron and called Energy Regeneration Brake by AMC. This completely battery powered urban concept car was recharged by braking, thus increasing the range of the automobile. The AMC Amitron was first use of regenerative braking technology in the U.S. A more recent working prototype of
1287-452: A devoted base of owners. A second-generation Insight was launched in 2010. In 2004, Honda also released a 6-cylinder hybrid version of the Accord but discontinued it in 2007, citing disappointing sales, although production of a 4-cylinder hybrid began in 2012. The Ford Escape Hybrid , the first hybrid electric sport utility vehicle (SUV), was released in 2005. Toyota and Ford entered into
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#17327874251001404-410: A flow field) enables the calculation of forces and moments acting on the object. In many aerodynamics problems, the forces of interest are the fundamental forces of flight: lift , drag , thrust , and weight . Of these, lift and drag are aerodynamic forces, i.e. forces due to air flow over a solid body. Calculation of these quantities is often founded upon the assumption that the flow field behaves as
1521-438: A fluid, the speed of sound in that fluid can be considered the fastest speed that "information" can travel in the flow. This difference most obviously manifests itself in the case of a fluid striking an object. In front of that object, the fluid builds up a stagnation pressure as impact with the object brings the moving fluid to rest. In fluid traveling at subsonic speed, this pressure disturbance can propagate upstream, changing
1638-422: A four-cylinder ICE and an electric motor. Below 15 mph (24 km/h) the electric motor alone drove the vehicle, drawing power from a battery pack, and above this speed the "main" engine cut in to take the car up to its 35 mph (56 km/h) top speed. About 600 were made up to 1918. The Woods hybrid was a commercial failure, proving to be too slow for its price, and too difficult to service. In England,
1755-414: A fundamental relationship between pressure, density, and flow velocity for incompressible flow known today as Bernoulli's principle , which provides one method for calculating aerodynamic lift. In 1757, Leonhard Euler published the more general Euler equations which could be applied to both compressible and incompressible flows. The Euler equations were extended to incorporate the effects of viscosity in
1872-658: A gasoline-powered vehicle. If the engine is not used to drive the car directly, it can be geared to run at maximum efficiency, further improving fuel economy. Ferdinand Porsche developed the Lohner–Porsche in 1901. But hybrid electric vehicles did not become widely available until the release of the Toyota Prius in Japan in 1997, followed by the Honda Insight in 1999. Initially, hybrid seemed unnecessary due to
1989-549: A licensing agreement in March 2004 allowing Ford to use 20 patents from Toyota related to hybrid technology, although Ford's engine was independently designed and built. In exchange for the hybrid licenses, Ford licensed patents involving their European diesel engines to Toyota. Toyota announced calendar year 2005 hybrid electric versions of the Toyota Highlander Hybrid and Lexus RX 400h with 4WD-i, which uses
2106-472: A partial solution to the problem of aerodynamic lift, which was becoming severe as sports car racing speeds increased during the 1950s. The design paradigm of sloping the tail to reduce drag was carried to an extreme on cars such as the Cunningham C-5R , resulting in an airfoil effect lifting the rear of the car at speed and so running the risk of instability or loss of control. The Kammback decreased
2223-519: A patent application for a gasoline-electric hybrid rail-car propulsion system in early 1889, and for a similar hybrid boat propulsion system in mid-1889. He went on to test and market the Patton Motor Car, a gas-electric hybrid system used to drive tram cars and small locomotives . A gasoline engine drove a generator that served to charge a lead acid battery in parallel with the traction motors. A conventional series-parallel controller
2340-513: A racing hybrid in 1902. In 1905, Henri Pieper of Germany/Belgium introduced a hybrid vehicle with an electric motor/generator, batteries, and a small gasoline engine. It used the electric motor to charge its batteries at cruise speed and used both motors to accelerate or climb a hill. The Pieper factory was taken over by Impéria , after Pieper died. The 1915 Dual Power , made by the Woods Motor Vehicle electric car maker, had
2457-410: A range of flow velocities just below and above the local speed of sound (generally taken as Mach 0.8–1.2). It is defined as the range of speeds between the critical Mach number , when some parts of the airflow over an aircraft become supersonic , and a higher speed, typically near Mach 1.2 , when all of the airflow is supersonic. Between these speeds, some of the airflow is supersonic, while some of
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#17327874251002574-491: A rear electric motor to power the rear wheels, negating the need for a transfer case. In 2006, General Motors Saturn Division began to market a mild parallel hybrid , the 2007 Saturn Vue Green Line , which utilized GM's Belted Alternator /Starter ( BAS Hybrid ) system combined with a 2.4-litre L4 engine and an FWD automatic transmission. The same hybrid powertrain was also used to power the 2008 Saturn Aura Green Line and Malibu Hybrid models. As of December 2009 , only
2691-628: A resurgence in the early 2000s as a method to reduce fuel consumption in hybrid electric vehicles . Several cars have been marketed as Kammbacks despite their profiles not adhering to the aerodynamic philosophy of a true Kammback. These models include the 1971–1977 Chevrolet Vega Kammback wagon, the 1981–1982 AMC Eagle Kammback, the AMC AMX-GT , and the Pontiac Firebird –based "Type K" concept cars. Some models that are marketed as " coupes "—such as BMW and Mercedes-Benz SUVs like
2808-535: A second-generation Prius in 2004 and a third in 2009. The 2010 Prius has an estimated U.S. Environmental Protection Agency combined fuel economy cycle of 50 miles per US gallon (4.7 L/100 km; 60 mpg ‑imp ). The Audi Duo III was introduced in 1997, based on the Audi B5 A4 Avant , and was the only Duo to ever make it into series production. The Duo III used the 1.9- litre Turbocharged Direct Injection (TDI) diesel engine , which
2925-419: Is a "teardrop," a smooth airfoil -like shape, but it is not practical for road vehicles because of size constraints. However, researchers, including Kamm, found that abruptly cutting off the tail resulted in a minimal increase in drag. The reason for this is that a turbulent wake region forms behind the vertical surface at the rear of the car. This wake region mimics the effect of the tapered tail in that air in
3042-418: Is a flow in which density is constant in both time and space. Although all real fluids are compressible, a flow is often approximated as incompressible if the effect of the density changes cause only small changes to the calculated results. This is more likely to be true when the flow speeds are significantly lower than the speed of sound. Effects of compressibility are more significant at speeds close to or above
3159-448: Is a solution in one dimension to both the momentum and energy conservation equations. The ideal gas law or another such equation of state is often used in conjunction with these equations to form a determined system that allows the solution for the unknown variables. Aerodynamic problems are classified by the flow environment or properties of the flow, including flow speed , compressibility , and viscosity . External aerodynamics
3276-416: Is a subset of the supersonic regime. Hypersonic flow is characterized by high temperature flow behind a shock wave, viscous interaction, and chemical dissociation of gas. The incompressible and compressible flow regimes produce many associated phenomena, such as boundary layers and turbulence. The concept of a boundary layer is important in many problems in aerodynamics. The viscosity and fluid friction in
3393-453: Is a type of hybrid vehicle that combines a conventional internal combustion engine (ICE) system with an electric propulsion system ( hybrid vehicle drivetrain ). The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle or better performance. There is a variety of HEV types and the degree to which each functions as an electric vehicle (EV) also varies. The most common form of HEV
3510-503: Is associated with the frictional forces in a flow. In some flow fields, viscous effects are very small, and approximate solutions may safely neglect viscous effects. These approximations are called inviscid flows. Flows for which viscosity is not neglected are called viscous flows. Finally, aerodynamic problems may also be classified by the flow environment. External aerodynamics is the study of flow around solid objects of various shapes (e.g. around an airplane wing), while internal aerodynamics
3627-407: Is called laminar flow . Aerodynamics is a significant element of vehicle design , including road cars and trucks where the main goal is to reduce the vehicle drag coefficient , and racing cars , where in addition to reducing drag the goal is also to increase the overall level of downforce . Aerodynamics is also important in the prediction of forces and moments acting on sailing vessels . It
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3744-409: Is called potential flow and allows the differential equations that describe the flow to be a simplified version of the equations of fluid dynamics , thus making available to the aerodynamicist a range of quick and easy solutions. In solving a subsonic problem, one decision to be made by the aerodynamicist is whether to incorporate the effects of compressibility. Compressibility is a description of
3861-403: Is delivered by each of the energy sources on-board of the vehicle. The recovered energy can be stored in the battery and deployed at a later time to assist the prime mover to provide tractive power. This is why all hybrid vehicles include an energy management controller, interposed between the driver and the component controllers. As mentioned, the aim of the energy management system is to determine
3978-457: Is the hybrid electric car, although hybrid electric trucks (pickups and tractors), buses, boats, tow trucks, and aircraft also exist. Modern HEVs make use of efficiency-improving technologies such as regenerative brakes which convert the vehicle's kinetic energy to electric energy, which is stored in a battery or supercapacitor . Some varieties of HEV use an internal combustion engine to turn an electrical generator , which either recharges
4095-497: Is the study of flow around solid objects of various shapes. Evaluating the lift and drag on an airplane or the shock waves that form in front of the nose of a rocket are examples of external aerodynamics. Internal aerodynamics is the study of flow through passages in solid objects. For instance, internal aerodynamics encompasses the study of the airflow through a jet engine or through an air conditioning pipe. Aerodynamic problems can also be classified according to whether
4212-415: Is the study of flow through passages inside solid objects (e.g. through a jet engine). Unlike liquids and solids, gases are composed of discrete molecules which occupy only a small fraction of the volume filled by the gas. On a molecular level, flow fields are made up of the collisions of many individual of gas molecules between themselves and with solid surfaces. However, in most aerodynamics applications,
4329-426: Is used because gas flows with a Mach number below that value demonstrate changes in density of less than 5%. Furthermore, that maximum 5% density change occurs at the stagnation point (the point on the object where flow speed is zero), while the density changes around the rest of the object will be significantly lower. Transonic, supersonic, and hypersonic flows are all compressible flows. The term Transonic refers to
4446-418: Is used in the design of mechanical components such as hard drive heads. Structural engineers resort to aerodynamics, and particularly aeroelasticity , when calculating wind loads in the design of large buildings, bridges , and wind turbines . The aerodynamics of internal passages is important in heating/ventilation , gas piping , and in automotive engines where detailed flow patterns strongly affect
4563-468: Is used to classify flows according to speed regime. Subsonic flows are flow fields in which the air speed field is always below the local speed of sound. Transonic flows include both regions of subsonic flow and regions in which the local flow speed is greater than the local speed of sound. Supersonic flows are defined to be flows in which the flow speed is greater than the speed of sound everywhere. A fourth classification, hypersonic flow, refers to flows where
4680-490: The Ancient Greek legend of Icarus and Daedalus . Fundamental concepts of continuum , drag , and pressure gradients appear in the work of Aristotle and Archimedes . In 1726, Sir Isaac Newton became the first person to develop a theory of air resistance, making him one of the first aerodynamicists. Dutch - Swiss mathematician Daniel Bernoulli followed in 1738 with Hydrodynamica in which he described
4797-467: The Esparante GTR-Q9 became the first Petrol-Electric Hybrid to race at Le Mans, although the car failed to qualify for the main event. The car managed to finished second in class at Petit Le Mans the same year. Automotive hybrid technology became widespread beginning in the late 1990s. The first mass-produced hybrid vehicle was the Toyota Prius , launched in Japan in 1997, and followed by
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4914-571: The Honda Insight , launched in 1999 in the United States and Japan. The Prius was launched in Europe , North America and the rest of the world in 2000. The first-generation Prius sedan has an estimated fuel economy of 52 miles per US gallon (4.5 L/100 km; 62 mpg ‑imp ) in the city and 45 miles per US gallon (5.2 L/100 km; 54 mpg ‑imp ) in highway driving. The two-door first-generation Insight
5031-535: The Kia Optima Hybrid . The Peugeot 3008 HYbrid4 was launched in the European market in 2012, becoming the world's first production diesel -electric hybrid. According to Peugeot the new hybrid delivers a fuel economy of up to 62 miles per US gallon (3.8 L/100 km; 74 mpg ‑imp ) and CO 2 emissions of 99g/km on the European test cycle. The Toyota Prius v , launched in
5148-794: The Mercedes-Benz ML450 Hybrid by lease only. Sales of the Honda CR-Z began in Japan in February 2010, followed by the U.S. and European markets later in the year, becoming Honda's third hybrid electric car in the market. Honda also launched the 2011 Honda Fit Hybrid in Japan in October 2010, and unveiled the European version, the Honda Jazz Hybrid, at the 2010 Paris Motor Show , which went on sale in some European markets by early 2011. Mass production of
5265-586: The Mercury Milan Hybrid . The Hyundai Elantra LPI Hybrid was unveiled at the 2009 Seoul Motor Show , and sales began in the South Korean domestic market in July 2009. The Elantra LPI (Liquefied Petroleum Injected) is the world's first hybrid vehicle to be powered by an internal combustion engine built to run on liquefied petroleum gas (LPG) as a fuel. The Elantra PLI is a mild hybrid and
5382-644: The Toyota Motor Corporation with more than 15 million Lexus and Toyota hybrids sold as of January 2020 , followed by Honda Motor Co., Ltd. with cumulative global sales of more than 1.35 million hybrids as of June 2014 ; As of September 2022 , worldwide hybrid sales are led by the Toyota Prius liftback, with cumulative sales of 5 million units. The Prius nameplate had sold more than 6 million hybrids up to January 2017. Global Lexus hybrid sales achieved
5499-683: The Volkswagen Jetta Hybrid were released in the U.S. in December 2012. Global sales of the Toyota Prius liftback passed the 3 million milestone in June 2013. The Prius liftbak is available in almost 80 countries and regions, and it is the world's best-selling hybrid electric vehicle. Toyota released the hybrid versions of the Corolla Axio sedan and Corolla Fielder station wagon in Japan in August 2013. Both cars are equipped with
5616-535: The X6 and GLC Coupé —"use a sort-of Kammback shape, though their tail ends have a few more lumps and bumps than a proper Kammback ought to have." Cars that have had a Kammback include: + 1958-1963 Lotus Elite Aerodynamics Modern aerodynamics only dates back to the seventeenth century, but aerodynamic forces have been harnessed by humans for thousands of years in sailboats and windmills, and images and stories of flight appear throughout recorded history, such as
5733-416: The flow speed is below, near or above the speed of sound . A problem is called subsonic if all the speeds in the problem are less than the speed of sound, transonic if speeds both below and above the speed of sound are present (normally when the characteristic speed is approximately the speed of sound), supersonic when the characteristic flow speed is greater than the speed of sound, and hypersonic when
5850-557: The "Big Three" would be able to move from the concept phase to cost effective, pre-production prototype vehicles by 2004, as set out in Goal 3. The program was replaced by the hydrogen-focused FreedomCAR initiative by the George W. Bush administration in 2001, an initiative to fund research too risky for the private sector to engage in, with the long-term goal of developing effectively carbon emission- and petroleum-free vehicles. 1998 saw
5967-445: The 1 million unit milestone in March 2016. As of January 2017 , the conventional Prius is the all-time best-selling hybrid car in both Japan and the U.S., with sales of over 1.8 million in Japan and 1.75 million in the U.S. Hybrid electric vehicles can be classified according to the way in which power is supplied to the drivetrain: In each of the hybrids above it is common to use regenerative braking to recharge
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#17327874251006084-721: The 1970 Federal Clean Car Incentive Program, but the program was stopped by the United States Environmental Protection Agency (EPA) in 1976 while Eric Stork, the head of the EPA's vehicle emissions control program at the time, was accused of a prejudicial coverup . In 1979 the Fiat 131 Ibrido was presented in Detroit, a marching prototype made by the CRF (Fiat Research Center). The engine compartment
6201-578: The 2009 Cadillac Escalade Hybrid version. For the 2009 model year, General Motors released the same technology in their half-ton pickup truck models, the 2009 Chevrolet Silverado and GMC Sierra Two-Mode Hybrid models. The Ford Fusion Hybrid officially debuted at the Greater Los Angeles Auto Show in November 2008, and was launched to the U.S. market in March 2009, together with the second-generation Honda Insight and
6318-614: The 2011 Toyota Auris Hybrid began in May 2010 at Toyota Manufacturing UK (TMUK) Burnaston plant and became the first mass-produced hybrid vehicle to be built in Europe. Sales in the UK began in July 2010, at a price starting at £18,950 ( US$ 27,450 ), £550 ( US$ 800 ) less than the Toyota Prius . The 2011 Auris Hybrid shares the same powertrain as the Prius, and combined fuel economy is 74.3 mpg ‑imp (3.80 L/100 km; 61.9 mpg ‑US ). The 2011 Lincoln MKZ Hybrid
6435-567: The Audi Duo (the Audi C3 100 Avant Duo ) experimental vehicle, a plug-in parallel hybrid based on the Audi 100 Avant quattro . This car had a 9.4 kilowatts (12.8 PS ; 12.6 bhp ) Siemens electric motor which drove the rear roadwheels. A trunk -mounted nickel–cadmium battery supplied energy to the motor that drove the rear wheels. The vehicle's front roadwheels were powered by
6552-784: The BAS-equipped Malibu is still in (limited) production. In 2007, Lexus released a hybrid electric version of their GS sport sedan, the GS 450h , with a power output of 335 bhp. The 2007 Camry Hybrid became available in summer 2006 in the United States and Canada. Nissan launched the Altima Hybrid with technology licensed by Toyota in 2007. Commencing in fall 2007, General Motors began to market their 2008 Two-Mode Hybrid models of their GMT900 -based Chevrolet Tahoe and GMC Yukon SUVs, closely followed by
6669-570: The HEV was built by Victor Wouk (one of the scientists involved with the Henney Kilowatt , the first transistor-based electric car) and Dr. Charles L Rosen. Wouk's work with HEVs in the 1960s and 1970s earned him the title as the "Godfather of the Hybrid". They installed a prototype hybrid drivetrain (with a 16-kilowatt (21 hp) electric motor ) into a 1972 Buick Skylark provided by GM for
6786-603: The U.S. during 2012 are the Audi Q5 Hybrid , BMW 5 Series ActiveHybrid , BMW 3 series Hybrid , Ford C-Max Hybrid , Acura ILX Hybrid . Also during 2012 were released the next generation of Toyota Camry Hybrid and the Ford Fusion Hybrid , both of which offer significantly improved fuel economy in comparison with their previous generations. The 2013 models of the Toyota Avalon Hybrid and
6903-711: The U.S. in 2011. VW also announced plans to introduce diesel -electric hybrid versions of its most popular models in 2012, beginning with the new Jetta , followed by the Golf Hybrid in 2013 together with hybrid versions of the Passat . Other gasoline-electric hybrids released in the U.S. in 2011 were the Lexus CT 200h , the Infiniti M35 Hybrid , the Hyundai Sonata Hybrid and its sibling
7020-553: The U.S. in October 2009. The S400 BlueHybrid is a mild hybrid and the first hybrid car to adopt a lithium-ion battery . The hybrid technology in the S400 was co-developed by Daimler AG and BMW . The same hybrid technology is being used in the BMW ActiveHybrid 7 , expected to go on sales in the U.S. and Europe by mid-2010. In December 2009 BMW began sales of its full hybrid BMW ActiveHybrid X6 , while Daimler launched
7137-710: The U.S. in October 2011, is the first spinoff from the Prius family. Sales in Japan began in May 2011 as the Prius Alpha. The European version, named Prius +, was launched in June 2012. The Prius Aqua was launched in Japan in December 2011, and was released as the Toyota Prius c in the U.S. in March 2012. The Prius c was launched in Australia in April 2012. The production version of the 2012 Toyota Yaris Hybrid went on sale in Europe in June 2012. Other hybrids released in
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#17327874251007254-412: The air is approximated as being significant only in this thin layer. This assumption makes the description of such aerodynamics much more tractable mathematically. In aerodynamics, turbulence is characterized by chaotic property changes in the flow. These include low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time. Flow that is not turbulent
7371-568: The airflow is not supersonic. Supersonic aerodynamic problems are those involving flow speeds greater than the speed of sound. Calculating the lift on the Concorde during cruise can be an example of a supersonic aerodynamic problem. Supersonic flow behaves very differently from subsonic flow. Fluids react to differences in pressure; pressure changes are how a fluid is "told" to respond to its environment. Therefore, since sound is, in fact, an infinitesimal pressure difference propagating through
7488-580: The amount of change of density in the flow. When the effects of compressibility on the solution are small, the assumption that density is constant may be made. The problem is then an incompressible low-speed aerodynamics problem. When the density is allowed to vary, the flow is called compressible. In air, compressibility effects are usually ignored when the Mach number in the flow does not exceed 0.3 (about 335 feet (102 m) per second or 228 miles (366 km) per hour at 60 °F (16 °C)). Above Mach 0.3,
7605-483: The area of the lifting surface while creating a low-pressure zone underneath the tail. Some studies showed that the addition of a rear spoiler to a Kammback design was not beneficial because the overall drag increased with the angles that were studied. In 1959, the Kammback came into use on full-body racing cars as an anti-lift measure, and within a few years would be used on virtually all such vehicles. The design had
7722-439: The batteries. A plug-in hybrid electric vehicle (PHEV), also known as a plug-in hybrid, is a hybrid electric vehicle with rechargeable batteries that can be restored to full charge by connecting a plug to an external electric powersource . A PHEV shares the characteristics of both a conventional hybrid electric vehicle, having an electric motor and an internal combustion engine ; and of an all-electric vehicle , also having
7839-465: The battery is essential. In a conventional (non-hybrid) vehicle, there is no need for an energy management strategy: the driver decides the instant power delivery using the brake and accelerator pedals and, in manual transmission vehicles, decides which gear is engaged at any time. In a hybrid vehicle, on the other hand, there is an additional decision that must be taken due to its ability to recover energy during braking or driving downhill: how much power
7956-860: The battery storage, the Volvo ECC used a gas turbine engine to drive the generator for recharging. The Clinton administration initiated the Partnership for a New Generation of Vehicles (PNGV) program on 29 September 1993, that involved Chrysler , Ford , General Motors , USCAR , the DoE , and other various governmental agencies to engineer the next efficient and clean vehicle. The United States National Research Council (USNRC) cited automakers ' moves to produce HEVs as evidence that technologies developed under PNGV were being rapidly adopted on production lines , as called for under Goal 2. Based on information received from automakers, NRC reviewers questioned whether
8073-603: The brakes and by igniting oxyhydrogen gas. No production beyond the prototype was reported. During the Second World War, Ferdinand Porsche sought to use his firm's experience in hybrid drivetrain design for powering armored fighting vehicles for Nazi Germany. A series of designs, starting with the VK 3001 (P) , the unsuccessful VK 4501 (P) heavy tank prototype (which became the Elefant tank destroyer) and concluding with
8190-690: The choice between statistical mechanics and the continuous formulation of aerodynamics. The assumption of a fluid continuum allows problems in aerodynamics to be solved using fluid dynamics conservation laws . Three conservation principles are used: Together, these equations are known as the Navier–Stokes equations , although some authors define the term to only include the momentum equation(s). The Navier–Stokes equations have no known analytical solution and are solved in modern aerodynamics using computational techniques . Because computational methods using high speed computers were not historically available and
8307-462: The continuum assumption is reasonable. The continuum assumption is less valid for extremely low-density flows, such as those encountered by vehicles at very high altitudes (e.g. 300,000 ft/90 km) or satellites in Low Earth orbit . In those cases, statistical mechanics is a more accurate method of solving the problem than is continuum aerodynamics. The Knudsen number can be used to guide
8424-401: The design in the 1930s. Some vehicles incorporate the kammback design based on aerodynamic principles, while some use a cut-off tail as a design or marketing feature. As the speed of cars increased during the 1920s and 1930s, designers observed and began to apply the principles of automotive aerodynamics . As aerodynamic drag increases, more energy, and thus more fuel, is required to propel
8541-463: The desire to improve the aerodynamic efficiency of current aircraft and propulsion systems, continues to motivate new research in aerodynamics, while work continues to be done on important problems in basic aerodynamic theory related to flow turbulence and the existence and uniqueness of analytical solutions to the Navier–Stokes equations. Understanding the motion of air around an object (often called
8658-437: The discrete molecular nature of gases is ignored, and the flow field is assumed to behave as a continuum . This assumption allows fluid properties such as density and flow velocity to be defined everywhere within the flow. The validity of the continuum assumption is dependent on the density of the gas and the application in question. For the continuum assumption to be valid, the mean free path length must be much smaller than
8775-491: The early days, the Armstrong Phaeton was innovative with many firsts. Not only did it have a gasoline powered 6.5-liter, two-cylinder engine, but also a dynamo flywheel connected to an onboard battery. The dynamo and regenerative braking were used to charge the battery. Its electric starter was used 16 years before Cadillac's. The dynamo also provided ignition spark and powered the electric lamps. The Phaeton also had
8892-422: The effectiveness of the design. In 1938, Kamm produced a prototype using a Kammback shape, based on a BMW 328 . The Kammback, along with other aerodynamic modifications, gave the prototype a drag coefficient of 0.25. The earliest mass-produced cars using Kammback principles were the 1949–1951 Nash Airflyte in the United States and the 1952–1955 Borgward Hansa 2400 in Europe. The ideal shape to minimize drag
9009-694: The electric motor is keyed, the latter powered by a 12-batteries pack. The regenerative brake concept was further developed in the early 1980s by David Arthurs, an electrical engineer , using off-the shelf components, military surplus, and an Opel GT . The voltage controller to link the batteries, motor (a jet-engine starter motor), and DC generator was Arthurs'. The vehicle exhibited 75 miles per US gallon (3.1 L/100 km; 90 mpg ‑imp ) fuel efficiency , and plans for it were marketed by Mother Earth News . In 1982, Fritz Karl Preikschat invented an electric propulsion and braking system for cars based on regenerative braking. While clearly not
9126-603: The first flights, Frederick W. Lanchester , Martin Kutta , and Nikolai Zhukovsky independently created theories that connected circulation of a fluid flow to lift. Kutta and Zhukovsky went on to develop a two-dimensional wing theory. Expanding upon the work of Lanchester, Ludwig Prandtl is credited with developing the mathematics behind thin-airfoil and lifting-line theories as well as work with boundary layers . As aircraft speed increased designers began to encounter challenges associated with air compressibility at speeds near
9243-453: The first half of the 1800s, resulting in the Navier–Stokes equations . The Navier–Stokes equations are the most general governing equations of fluid flow but are difficult to solve for the flow around all but the simplest of shapes. In 1799, Sir George Cayley became the first person to identify the four aerodynamic forces of flight ( weight , lift , drag , and thrust ), as well as the relationships between them, and in doing so outlined
9360-412: The first hybrid to adopt advanced lithium polymer (Li–Poly) batteries. The Elantra LPI Hybrid delivers a fuel economy rating of 41.9 miles per US gallon (5.61 L/100 km; 50.3 mpg ‑imp ) and CO 2 emissions of 99 g/km to qualify as a Super Ultra Low Emission Vehicle (SULEV). The Mercedes-Benz S400 BlueHybrid was unveiled in the 2009 Chicago Auto Show , and sales began in
9477-587: The first semi-automatic transmission (no manual clutch). The exhaust system was an integrated structural component of the vehicle. The Armstrong Phaeton's motor was too powerful; the torque damaged the carriage wheels repeatedly. In 1900, while employed at Lohner Coach Factory, Ferdinand Porsche developed the Mixte , a 4WD series-hybrid version of " System Lohner–Porsche " electric carriage that previously appeared in 1900 Paris World Fair . George Fischer sold hybrid buses to England in 1901; Knight Neftal produced
9594-470: The first version of a flex-fuel hybrid powered by a 1.8-litre Atkinson engine. By February 2020, sales of the Corolla Altis flex-fuel hybrid represented almost 25% of all Corolla sales in the country. To take advantage of the emission reduction potential of hybrid electric vehicles (HEVs), appropriate design of their energy management systems (EMSs) to control the power flow between the engine and
9711-477: The flow pattern ahead of the object and giving the impression that the fluid "knows" the object is there by seemingly adjusting its movement and is flowing around it. In a supersonic flow, however, the pressure disturbance cannot propagate upstream. Thus, when the fluid finally reaches the object it strikes it and the fluid is forced to change its properties – temperature , density , pressure , and Mach number —in an extremely violent and irreversible fashion called
9828-458: The flow speed is much greater than the speed of sound. Aerodynamicists disagree on the precise definition of hypersonic flow. Compressible flow accounts for varying density within the flow. Subsonic flows are often idealized as incompressible, i.e. the density is assumed to be constant. Transonic and supersonic flows are compressible, and calculations that neglect the changes of density in these flow fields will yield inaccurate results. Viscosity
9945-570: The flow speed is much greater than the speed of sound. Aerodynamicists disagree over the precise definition of hypersonic flow; a rough definition considers flows with Mach numbers above 5 to be hypersonic. The influence of viscosity on the flow dictates a third classification. Some problems may encounter only very small viscous effects, in which case viscosity can be considered to be negligible. The approximations to these problems are called inviscid flows . Flows for which viscosity cannot be neglected are called viscous flows. An incompressible flow
10062-461: The free stream does not enter this region (avoiding boundary layer separation ); therefore, smooth airflow is maintained, minimizing drag. Kamm's design is based on the tail being truncated at the point where the cross section area is 50% of the car's maximum cross-section, which Kamm found represented a good compromise, as by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds. The Kammback presented
10179-618: The heaviest armored fighting vehicle ever prototyped, the Panzerkampfwagen Maus of nearly 190 tonnes in weight, were just two examples of a number of planned Wehrmacht "weapons systems" (including the highly-"electrified" subsystems on the Fw 191 bomber project ), crippled in their development by the then-substandard supplies of electrical-grade copper , required for the electric final drives on Porsche's armored fighting vehicle powertrain designs. The regenerative braking system ,
10296-465: The high computational cost of solving these complex equations now that they are available, simplifications of the Navier–Stokes equations have been and continue to be employed. The Euler equations are a set of similar conservation equations which neglect viscosity and may be used in cases where the effect of viscosity is expected to be small. Further simplifications lead to Laplace's equation and potential flow theory. Additionally, Bernoulli's equation
10413-433: The length scale of the application in question. For example, many aerodynamics applications deal with aircraft flying in atmospheric conditions, where the mean free path length is on the order of micrometers and where the body is orders of magnitude larger. In these cases, the length scale of the aircraft ranges from a few meters to a few tens of meters, which is much larger than the mean free path length. For such applications,
10530-487: The low cost of gasoline. Worldwide increases in the price of petroleum caused many automakers to release hybrids in the late 2000s; they are now perceived as a core segment of the automotive market of the future. As of April 2020 , over 17 million hybrid electric vehicles have been sold worldwide since their inception in 1997. Japan has the world's largest hybrid electric vehicle fleet with 7.5 million hybrids registered as of March 2018 . Japan also has
10647-558: The milestone of 400,000 hybrid electric vehicles produced in November 2014. After 18 years since the introduction of hybrid cars, Japan became in 2014 the first country to reach sales of over 1 million hybrid cars in a single year, and also the Japanese market surpassed the United States as the world's largest hybrid market. The redesigned and more efficient fourth generation Prius was released for retail customers in Japan in December 2015. The 2016 model year Prius Eco surpassed
10764-500: The non-hybrid version, but delivers 50 miles per US gallon (4.7 L/100 km; 60 mpg ‑imp ), a 40 percent increase compared to a conventional Civic LX sedan. Along with the conventional Civic, it received a styling update for 2004. The redesigned 2004 Toyota Prius (second generation) improved passenger room, cargo area, and power output, while increasing energy efficiency and reducing emissions. The Honda Insight first generation stopped being produced after 2006 and has
10881-550: The only patent relating to the hybrid electric vehicle, the patent was important based on 120+ subsequent patents directly citing it. The patent was issued in the U.S. and the system was not prototyped or commercialized. In 1988, Alfa Romeo built three prototypes of the Alfa 33 Hybrid, equipped with the tried and tested Alfasud boxer engine (1,500cc, 95 HP) combined with a three-phase asynchronous electric motor (16 HP, 6.1 kgm of torque) supplied by Ansaldo of Genoa . The design
10998-412: The optimal power split between the on-board energy sources. The decision regarding what to consider optimal depends on the specific application: in most cases, the strategies tend to minimize the fuel consumption, but optimization objectives could also include the minimization of pollutant emissions, maximization of battery life or—in general—a compromise among all the above goals. William H. Patton filed
11115-403: The path toward achieving heavier-than-air flight for the next century. In 1871, Francis Herbert Wenham constructed the first wind tunnel , allowing precise measurements of aerodynamic forces. Drag theories were developed by Jean le Rond d'Alembert , Gustav Kirchhoff , and Lord Rayleigh . In 1889, Charles Renard , a French aeronautical engineer, became the first person to reasonably predict
11232-579: The performance of the engine. Urban aerodynamics are studied by town planners and designers seeking to improve amenity in outdoor spaces, or in creating urban microclimates to reduce the effects of urban pollution. The field of environmental aerodynamics describes ways in which atmospheric circulation and flight mechanics affect ecosystems. Aerodynamic equations are used in numerical weather prediction . Sports in which aerodynamics are of crucial importance include soccer , table tennis , cricket , baseball , and golf , in which most players can control
11349-485: The point where entire aircraft can be designed using computer software, with wind-tunnel tests followed by flight tests to confirm the computer predictions. Understanding of supersonic and hypersonic aerodynamics has matured since the 1960s, and the goals of aerodynamicists have shifted from the behaviour of fluid flow to the engineering of a vehicle such that it interacts predictably with the fluid flow. Designing aircraft for supersonic and hypersonic conditions, as well as
11466-459: The power needed for sustained flight. Otto Lilienthal , the first person to become highly successful with glider flights, was also the first to propose thin, curved airfoils that would produce high lift and low drag. Building on these developments as well as research carried out in their own wind tunnel, the Wright brothers flew the first powered airplane on December 17, 1903. During the time of
11583-421: The problem flow should be described using compressible aerodynamics. According to the theory of aerodynamics, a flow is considered to be compressible if the density changes along a streamline . This means that – unlike incompressible flow – changes in density are considered. In general, this is the case where the Mach number in part or all of the flow exceeds 0.3. The Mach 0.3 value is rather arbitrary, but it
11700-507: The prototype Lanchester petrol-electric car was made in 1927. It was not a success, but the vehicle is on display in Thinktank, Birmingham Science Museum . The United States Army 's 1928 Experimental Motorized Force tested a gasoline-electric bus in a truck convoy. In 1931, Erich Gaichen invented and drove from Altenburg to Berlin a 1/2 horsepower electric car containing features later incorporated into hybrid cars. Its maximum speed
11817-538: The same engine. Two years later, Audi, unveiled the second duo generation, the Audi 100 Duo – likewise based on the Audi 100 Avant quattro. Once again, this featured an electric motor, a 21.3 kilowatts (29.0 PS; 28.6 bhp) three-phase machine, driving the rear roadwheels. This time, however, the rear wheels were additionally powered via the Torsen centre differential from the main engine compartment, which housed
11934-450: The speed of sound. The Mach number is used to evaluate whether the incompressibility can be assumed, otherwise the effects of compressibility must be included. Subsonic (or low-speed) aerodynamics describes fluid motion in flows which are much lower than the speed of sound everywhere in the flow. There are several branches of subsonic flow but one special case arises when the flow is inviscid , incompressible and irrotational . This case
12051-459: The speed of sound. The differences in airflow under such conditions lead to problems in aircraft control, increased drag due to shock waves , and the threat of structural failure due to aeroelastic flutter . The ratio of the flow speed to the speed of sound was named the Mach number after Ernst Mach who was one of the first to investigate the properties of the supersonic flow. Macquorn Rankine and Pierre Henri Hugoniot independently developed
12168-446: The theory for flow properties before and after a shock wave , while Jakob Ackeret led the initial work of calculating the lift and drag of supersonic airfoils. Theodore von Kármán and Hugh Latimer Dryden introduced the term transonic to describe flow speeds between the critical Mach number and Mach 1 where drag increases rapidly. This rapid increase in drag led aerodynamicists and aviators to disagree on whether supersonic flight
12285-480: The trajectory of the ball using the " Magnus effect ". General aerodynamics Subsonic aerodynamics Transonic aerodynamics Supersonic aerodynamics Hypersonic aerodynamics History of aerodynamics Aerodynamics related to engineering Ground vehicles Fixed-wing aircraft Helicopters Missiles Model aircraft Related branches of aerodynamics Aerothermodynamics Hybrid electric vehicle A hybrid electric vehicle ( HEV )
12402-417: The vehicle's batteries or directly powers its electric drive motors; this combination is known as a motor–generator . Many HEVs reduce idle emissions by shutting down the engine at idle and restarting it when needed; this is known as a start-stop system . A hybrid-electric produces lower tailpipe emissions than a comparably sized gasoline car since the hybrid's gasoline engine is usually smaller than that of
12519-456: The vehicle. In 1922, Paul Jaray patented a car based on a teardrop profile (i.e. with a rounded nose and long, tapered tail) to minimize the aerodynamic drag that is created at higher speeds. The streamliner vehicles of the mid 1930s—such as the Tatra 77 , Chrysler Airflow and Lincoln-Zephyr —were designed according to these discoveries. However, the long tail was not a practical shape for
12636-409: The world's highest hybrid market penetration with hybrids representing 19.0% of all passenger cars on the road as of March 2018 , both figures excluding kei cars . As of December 2020 , the U.S. ranked second with cumulative sales of 5.8 million units since 1999, and, as of July 2020 , Europe listed third with 3.0 million cars delivered since 2000. Global sales are led by
12753-645: Was 25 miles per hour (40 km/h), but it was licensed by the Motor Transport Office, taxed by the German Revenue Department and patented by the German Reichs-Patent Amt. The car battery was re-charged by the motor when the car went downhill. Additional power to charge the battery was provided by a cylinder of compressed air which was re-charged by small air pumps activated by vibrations of the chassis and
12870-490: Was achievable until the sound barrier was broken in 1947 using the Bell X-1 aircraft. By the time the sound barrier was broken, aerodynamicists' understanding of the subsonic and low supersonic flow had matured. The Cold War prompted the design of an ever-evolving line of high-performance aircraft. Computational fluid dynamics began as an effort to solve for flow properties around complex objects and has rapidly grown to
12987-406: Was composed by the 903cc borrowed from the Fiat 127 , set to output 33 hp only and coupled to a 20 kW electric motor. The scheme proposed by Fiat is defined as "parallel hybrid": the petrol engine is connected to the differential with a 1:1 direct gear ratio, without gearbox, instead of the clutch there was an 8-inch torque converter followed by the transmission shaft on which the rotor of
13104-565: Was coupled with a 21 kilowatts (29 PS ; 28 bhp ) electric motor. Due to low demand for it because of its high price, only about sixty Audi Duos were produced. Until the release of the Audi Q7 Hybrid in 2008, the Duo was the only European hybrid ever put into production. The Honda Civic Hybrid was introduced in February 2002 as a 2003 model, based on the seventh-generation Civic . The 2003 Civic Hybrid appears identical to
13221-647: Was developed in partnership with several Brazilian federal universities, and a prototype was tested for six months using a Toyota Prius as development mule . Toyota announced plans to start series production of a flex hybrid electric car for the Brazilian market in the second half of 2019. The twelfth generation of the Corolla line-up was launched in Brazil in September 2019, which included an Altis trim with
13338-451: Was estimated at 61 miles per US gallon (3.9 L/100 km; 73 mpg ‑imp ) in city driving and 68 miles per US gallon (3.5 L/100 km; 82 mpg ‑imp ) on the highway. The Toyota Prius sold 300 units in 1997 and 19,500 in 2000, and cumulative worldwide Prius sales reached the one million mark in April 2008. By early 2010, the Prius global cumulative sales were estimated at 1.6 million units. Toyota launched
13455-421: Was realistic and already mass production-oriented, with minimal modifications to the standard body and a weight increase of only 150 kg (110 for the batteries, 20 for the electric engine and 10 for power electronics). The Alfa Romeo 33 Ibrida was able to travel up to 60 km/h in full electric mode, with a 5 km range, very good performance for the time. In 1989, Audi produced its first iteration of
13572-417: Was unveiled at the 2010 New York International Auto Show and sales began in the U.S. in September 2010. The MKZ Hybrid is the first hybrid version ever to have the same price as the gasoline-engine version of the same car. The Porsche Cayenne Hybrid was launched in the U.S. in late 2010. Volkswagen announced at the 2010 Geneva Motor Show the launch of the 2012 Touareg Hybrid , which went on sale on
13689-746: Was used for the traction motors . A prototype was built in 1889, an experimental tram car was run in Pullman, Illinois , in 1891, and a production locomotive was sold to a street railway company in Cedar Falls, Iowa , in 1897. In 1896, the Armstrong Phaeton was developed by Harry E. Dey and built by the Armstrong Company of Bridgeport, CT for the Roger Mechanical Carriage Company. Though there were steam, electric, and internal combustion vehicles introduced in
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