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A Review of Aerodynamic Fundamentals in Automobiles

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A Review of Aerodynamic Fundamentals in Automobiles Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1(2016), pp.12-17 IIJET A Review of Aerodynamic Fundamentals in Automobiles *Kartikeya Akojwar *Mechanical Department, Maulana Azad National Institute of Technology, Bhopal *Email Id:- [email protected] Abstract I. Introduction Automotive engineering has rendered a lot of scope to a Automotive aerodynamics is the field of study of blend of branches of study. One of them is the aerodynamic aerodynamics of all road vehicles. This study gained study of vehicle dynamics and its importance in design popularization with the instigation of automotive racing considerations of various automobiles. The history of which relied a lot on improvement in the vehicle`s aerodynamics dates back to a couple of centuries. Seeing performance by reducing the aerodynamic drag force. birds fly, man had always wanted to explore the domain Aerodynamics is a study of fluid flow and drawing conclusions based on the aerodynamic forces generated as a which was only limited to the flying species. Having result of this flow. Hence it a part of fluid mechanics wherein developed a lot of concepts and models and the world study of only one fluid is done, which is air. In fluid witnessing a variety of aero-enthusiasts who were either mechanical terms, road vehicles are assumed to be bluffed chauffeurs or airmen, the success of aerodynamics was bodies in very close proximity to the ground. Their geometry enormously celebrated by the people. With the advent of in detail is extremely complex with the flow around the engines driven vehicles, aerodynamic parameters became an internal and external recesses and cavities and rotating important point of research. Hence vehicle shape and wheels adding to this complexity. The fully three aesthetics gradually developed; which is evident from the dimensional flow over the vehicle with turbulent boundary evolution of vehicle design in the previous century. Applied layers, flow separation is common and may be followed by reattachment. Also being a close to ground conveyance, its aerodynamics gradually nurtured the automotive industry flow analysis becomes even more complicated. Large which has resulted in today`s sleek and streamlined vehicle turbulent wakes are formed at the rear when the vehicle body designs. The work on vehicle aerodynamics have led to ends and the air rejoins the free stream. These turbulent increase in automotive efficiencies as a result of decreased wakes in many cases contain longitudinal trailing vortices. drag forces and near edge vortices. This review paper The avoidance of separation or, if this is not possible, its discusses the importance of aerodynamics in vehicle control are among the main objectives of vehicle dynamics, its history from simple carriages to race cars and aerodynamics. In addition to this it is also important for various aerodynamic parameters attributing to vehicle vehicles to produce down force to improve traction and better the cornering abilities. Also among its other goals are performance. reducing drag and wind noise, minimizing noise emission Keywords: Aerodynamics, Design considerations, and preventing undesired lift forces and other causes of Automobile design aerodynamic instability at high speed. As is typical for bluff bodies, drag which is the key issue for most road vehicles is 12 Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1(2016), pp.12-17 IIJET mainly pressure drag. This is in contrast to aircraft and ships Negative lift is an important parameter which is to be which suffer primarily from friction drag. Automotive employed in road vehicles. While the process of weighing aerodynamics differs from aircraft aerodynamics in a number the relative importance of a set of needs from various of ways. disciplines is generally comparable to that in other branches of applied fluid mechanics, the situation in vehicle First, the characteristic shape of automobiles is much less aerodynamics is unique in that an additional category of streamlined compared to an aircraft. Second, the vehicle arguments has to be taken into account: art, fashion, operates very close to the ground, rather than in free air. aestheticsand taste. In contrast to technical and economic, Third, the operating speed are lower and hence drag is these additional arguments are subjective in nature and reduced considerably as aerodynamic drag varies as the cannot be quantified. The automobile market today is ruled square of speed. Fourth, a ground vehicle has fewer degrees of freedom than an aircraft, and its motion is comparatively lesser affected by aerodynamic forces. Fifth, passenger and commercial ground vehicles have very specific design constraints such as their intended purpose, high safety standards and certain regulations and certifications. With regard to automobile geometries, road vehicles comprise a large variety of configurations. Passenger cars, vans and buses are closed single bodies and on the other hand trucks and race cars can be of more than one body. The shape of road vehicle is not primarily determined by the need to Fig 1- Basic shapes used to design a blend of vehicles. generate specific aerodynamic effects as in the case of by lavish designs and aesthetic value of a vehicle. While airplanes where efforts are put in to reduce the frictional drag design gives technical requirements a form that is in accord and increase lift force. Unlike such design basis as in with fashion, the fundamental nature of fashion is getting airplanes, a road vehicle`s shape is primarily determined by adapted to ever changing modernization. Consequently, functional, economic and aesthetic arguments. The although vehicle aerodynamics is getting better and better, it aerodynamic characteristics are not usually generated is not progressing towards a single ultimate shape as in the intentionally, they are the consequences of other than case. To the contrary, it must come to terms with new shapes aerodynamic considerations, but not the reason, for the again and again. There is no question; however, that shape. These “other than aerodynamic characteristics” place aerodynamics does influence design. a number of constraints on vehicle aerodynamicists. For example, the size constraints of a road vehicle limits the length and width of the vehicle. Also the necessity to accommodate the mechanical components of a vehicle like the engine, steering assembly, brakes, suspensions and the transmission line places severe constraints on the shape designing parameters. Furthermore, mass and cost constraints, packaging constrains and market niche freezes the physical dimensions of the vehicle.Of course, aerodynamicists do not just work to analyze the aerodynamic Fig 2- Streamlines passing over a generic car design. parameters of a vehicle configured by mechanical engineers. Hence there is indeed some work space for aerodynamicists II. Successful and unsuccessful approaches to to work on designing automobiles. Depending upon the type, aerodynamics designs purpose and configuration the objectives of aerodynamicists vary widely. Low drag is desirable for all automobiles. 13 Imperial International Journal of Eco-friendly Technologies Vol.- 1, Issue-1(2016), pp.12-17 IIJET Centuries ago when automobiles were just invented and and garnered a lot of public appreciation and whose credit horse carriages soon started disappearing with engine actually goes to the initial failures and unsuccessful vehicle replacing the horses, the vehicle design wasn’t a big issue. models. All these approaches are elaborately pictured below. People then were more fascinated by the fact that an automatic machine had been invented which could power a vehicle or a carriage. So carriages initially were simply meant to accommodate the driver and the passengers and protect them from wind, rain or mud. But then gradually with the advent of aeronautics and aerodynamics becoming a topic of vast research, people started applying the concepts of aerodynamics to automobiles also. Hence begun the development of various aerodynamic designs of automobiles which proved to perform better compared to their counterparts. Then the only motive was to reduce the drag forces on the vehicle and thus designing an aerodynamically fit vehicle. For both airships and aircrafts streamlined shapes were developed which lowered drag significantly and Fig 5- The development in the shapes of increased the cruising speed of the vehicles with given vehicle body and the transition from engine power. Figure_ shows the initial attempts to designing completely streamlined to bluff car bodies. with streamlined bodied vehicles. These attempts were III. Development of car designs from viewpoint purely aerodynamic results applied onto automobiles. But of aerodynamicists then with a specified array of space requirements for automobiles, these pure aerodynamic concepts weren’t of After the initial failures, aerodynamicists understood that much use to the automotive industry. automobiles being completely different from airplanes, they had to be designed as per their design requirements and considerations. Consequently aerodynamicists started making vehicle models based on aerodynamic concepts and automobile designing considerations. Hence the main motive behind making an aerodynamically fit vehicle design was to Fig 3- Some examples of initial efforts at vehicle designs. reduce the overall drag force acting on the vehicle so as to improve its performance and efficiency. As a result for
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