Tons of stuff here, so i'll split it into two posts. Haven't read any of it myself, just found it

Introduction



"Still we do not know as the life is been born: if from the silicon crystal organization or from molecules to base carbon. We are not sure of where: if in the deep space, argillaceous mud or the water of the primiti to you oceans. Those that is sure is that, on our planet, the life has passed in the water the greater part of the time: 3,4 of the 3,8 billions of years that come attributed to them. Not there is therefore to be astonished that, with all this time on hand, the evolution has rendered the aquatic organisms extraordinarily efficient us. A fish that the water cleaves and an automobile that cleaves the air must face, to various scales due to the various speed of the two objects and to the various density of the two fluid, similar problems. Like pure a bird and an airplane. Talché for students and technicians, than in order to realize a plan generally on hand has a measurable time in years, always has been natural to address to the examples supplied from the nature: that on its plans it works viceversa for million years. For how much it supplies instruments in order to realize models and to carry out the most sophisticated calculations or precise simulations and much, the technology supplies in fact very little new ideas. Very many new cues continue therefore to arrive from the observation, often accidental, of phenomena that happen to outside of the atmosphere (in our case) automotive. Of some cues particularly curious joints in aerodynamic within we will take care ourselves in the continuation.

Drag Co



Some time makes (Agosto 2003) has spoken about “the traditional” aerodynamics, substantially daughter of the synthetic formula for the calculation of the resistance to the advance R: R = ½ Cx S d v2 where S is the frontal section of the vehicle, d the density of the air (than varied with the pressure and temperature) and v the speed of the vehicle regarding the air (than for effect of the wind and the hysteresis of the tires us is not necessarily that one indicated from the tachimetro). Coefficient Cx, the superstar of this formula, is a shape factor that indicates how much is efficient the vehicle in making to pass through the fluid the frontal section S. For the vehicle, to have a good aerodynamics is like having one inferior section: it is spoken about “equivalent section”, given from the product Cx x S. That allows between the other to compensate the effects of the constant increase of dimensions which the Houses have accustomed us: as an example Mercedes Class and has one frontal section of 2,21 m2, considerably greater regarding the 2,16 m2 of the previous one; but thanks to the reduction of the Cx to optimal value 0,26, the equivalent section is come down from 0,58 to 0,57 m2. Also Bmw puts into effect it them Series 5 benefits of same excellent the Cx obtained in spite of an analogous increase regarding the previous generation, and in similar ways. But which are these ways? In order every year' the 80 engineers are themselves concentrate on the profilatura and the elimination to you of the irregolarità of surface (from the handles to the rough connections of the auto body). The result a lot has been vehicles from the rounded off shape and not the particularly detached personality: from Audi 100 to Opel Omega, than in order to arrive to inferior values to 0,30 they have adopted favorable lines with windshield and rear window a lot tilts to you, long shapes to 3 volumes and very joined together, small mirrors careens to you, handles to passing. The epitome of this tendency it has been Honda Insight, conceived hybrid car of 1999 for the maximum economy of exercise: for this purpose not only it has a frontal section ridottissima, but a particular shape that one exceptional Cx of 0,25 are worth them. This value, but, is today to the capacity of cars with auto body the much less extreme one: beyond to cited Mercedes and Bmw; cars sport as Lexus LS 430 arrives to 0,26 without having to resort to the posterior wheels careened of the Insight. The reason soon is said: they have been developed strategies that allow to contain the resistance to the air also without to taper to the excess the superficial ones until making them somigliare the drop, the more efficient shape (Cx = 0,05). We can think next to the automobile that it is left over in the firm air like if same diving itself in water. It must open a passage in the fluid, than it must then richiudere to the shoulders after to be slipped on superficial the lateral ones. On these three moments the aerodynamic resistance of the car depends. The process, but, is complex much. A lot in order to begin, the car is more or little flat in the inferior and arch part in that advanced one. Consequently, the air that passes to them under covers little road than which passes to them over. Because the vein can richiudere, it is then necessary that the upper air moves more fastly than that inferior. Hour, the principle of Bernoulli establishes that the energy possessed from the air vein is constant fixed its pressure, the speed and the quota. Neglecting the effect of the variation of the quota, the obvious consequence is that if in a point the speed increases, the pressure diminishes: for which the pressure that shape under the auto body is advanced to that one on the roof. The automobile is behaved therefore like an airplane wing: the difference of speed of the air generates a pressure difference that pushes it towards the high. This push is said carrying capacity: it supports the airplane and it can render the automobiles completely unstable.

Technical



Curious, the aerodynamics suggestionò the carriage makers since the albori of motoring, moreover without the support of studies adapts to you: as well as it is true that first big wave of automobiles conceived like monoliths was one leviga you in the immediate post-war period: and us Lancia Flaminia carrozzata from Pininfarina (1957 wanted extraordinary) in order to interrupt the tradition of the wrapping shapes. Only in years Sixty, but, he began himself to study the problem seriously, and the engineers discovered many things. As an example, a slope of the inferior rear window to 20° concurred with the air to follow the line of the automobile nearly without to separate itself. The discovery gave impulse to the development of auto bodies “fastback” (to two volumes) and had its apex in the line of the Porsche from 935/78 race “Moby Dick”; today the better example is the profile of last the Ford Focus 3 doors.

The way in which the air vein it is detached from the profile of the car and forms the so-called “wake” is decisive. Paradoxicalally, in fact, the greater part of the aerodynamic resistance does not come from the front part but from that posterior one. In a classic sedan to 3 volumes with nearly vertical rear window, the air is separated to the top of the rear window typically, not succeeding to follow of the slope in order “richiuder”. Here the air slows down, increases the own pressure and inverts the own direction: a vortex is formed that is that recalls air from the posterior one and primes turbulence. The turbulence gets worse the Cx considerably: quite, if the nearly vertical rear window rather than is tilted of 30-35 degrees regarding the horizontal, (like in passed capitava) the air flow he becomes unstable and it can have negative repercussions on dynamics of march to high speeds.
Like the resistance, also the carrying capacity is tied to the surface and the square of the speed through a shape coefficient. In this case the auto bodies to two volumes are svantaggiate, because their faying surface with the flow particularly is extended. But at the beginnig of years Sixty, the engineers of the Ferrari discovered the benefits of the aileron: a shape of wing turned upside down posizionata in correspondence of the posterior extremity of the car, that it could effectively generate deportanza and opporsi to the carrying capacity, without to get worse the resistance excessive.



The 248 SP from endurance was the first car to mount an aileron, in 1962; the successive year, was continuation from unforgettable the 250 GTO from road. To render this solution popular she was above all Porsche, than the yields true and just a brand of factory beginning from the 911 RS of 1972, where the aileron reduced the carrying capacity to the high speeds of 75%. The aileron then turns aside good part of the flow, so as to fargli to leave the car without to accelerate too much. Moreover, separating the flow in two, it limits the turbulence formation. For being efficient, but, it must rather be installed up: like on the cars rally retort and much monovolume. Spoiler and miniskirts have instead the function to have of side the air flow that would pass under auto body. The air that passes under the body car is always harmful: the interference of the mechanical organs generates turbulence (increasing the resistance) and slows down the same flow (increasing the carrying capacity).

There is an other way to limit the pernicious effects of the air sottoscocca: to careen the bottom. This solution, inaugurated from the Ferrari F355, is by now continuation from the majority of the supersportswoman. A levigato and regular bottom, in fact, favors an increase of the speed of the air, diminishing the difference of speed between the advanced flows and those inferiors and therefore the pressure difference that generates the carrying capacity; and the turbulence diminishes also, improving the aerodynamic penetration. Once introduced the flat bottom, can then be gone beyond: having more regular flows, he is natural to canalize them in order to obtain, as an example, the cooling of discs brake and the transmission. And from the bottom careened to the extracting machines the step is short. The arrival of this solution mutuata from the Formula 1 and relative of the uncovered ground effect from the English planners of single-seater to the end of years' 60, must to the Ferrari F360, but it has by now spreaded. The principle is that one to control the flows with true and own channels that lead the air from the front part to that posterior one and from the bottom towards the high, so as to to obtain an ulterior contribution of deportanza (the Carrera Turbo, as an example, to 310 km/h has 27 kg in more regarding the Carrera S, deprives of flat bottom). But regarding how much he happens on the cars from great prize, the aerodynamics plays on the series cars a relatively smaller role. Other demands, as that one of space, have the precedence. An light reduction of the Cx does not have drastic effects on the consumptions, and if performances are not searched record in terms of energetic efficiency, like on Toyota Prius, Honda Insight or the WV Lupo 3L, a Cx from supremacy are sure secondary regarding the habitability and to the style. Here because the monovolume and the SUV can sfoggiare frontal sections therefore overed-measure to remove of fact meant to the search of a good penetration (which the with rinunciano honesty Hummer), and the New Beetle can equally pay the fascination of its line rétro with a value of aerodynamic penetration rétro: 0,38 (same of one Fiat Rhythm with mounted Rack). Of the rest the pavilion to circular section of the New Beetle is much neighbor to one average ball: a stocky object and with one pessima penetration. In principle, the shape of the car would have somigliare to that one of a fish. They rather make well the Porsche, whose the auto body “accompanies” the air vein richiuder; it is also true that this spiovente line is obtained to discapito of requirements that for the engineers, when they do not work on a Porsche, are more pressing: a wide and regular inner volume, blocks reduced, accessibility (beyond that presence) of a baggage car. The 911 then has a shape to nearly perfect wing, for which Cx must sacrifice part of its in order to fight the carrying capacity. It succeeds to us well, thanks also to ailerons very made: the Cx are passed from the 0,40 of the 930 to the 0,32 of the 997 although similar proportions much."