AERODYNAMICS OF ROAD VEHICLES HUCHO PDF
AERODYNAMICS OF ROAD. VEHICLES. Wolf-Heinrich. Hucho. Ostring 48, D- , Schwalbach (Ts), Germany. Gino Sovran. General Motors. Purchase Aerodynamics of Road Vehicles - 1st Edition. Print Book & E-Book. Editors: Wolf-Heinrich Hucho. eBook ISBN: Aerodynamics of road vehicles from fluid mechanics to vehicle engineering pdf. 3 years ago. views · Vehicle Body Engineering Bus Body Details. 3 years.
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AERODYNAMICS OF ROAD. VEHICLES. Wolf-Heinrich Hucho. Ostring 48, D- , Schwalbach (Ts), Germany. Gino Sovran. General Motors Research and. 1. Introduction to Automobile. Aerodynamics. Wolf-Heinrich Hucho. Scope. Basic Principles. Peculiarities of Vehicle Aerodynamics. Aerodynamics of Road Vehicles – a Challenge for Computational Fluid Dynamics. Wolf-Heinrich Hucho. Germany, [email protected] ABSTRACT.
About the Editor Automotive aerodynamics book wolf- Heinrich hucho - SlideShare ; Dec 30, Chapter 1 Introduction to automobile aerodynamics Wolf-Heinrich Hucho 1. Aerodynamics of road vehicles from fluid mechanics to vehicle engineering pdf. The aerodynamic ow over a blu In fluid mechanical terms, road vehicles are bluff Aerodynamics of Road Vehicles — 4th edition. Edited by W-H. Materials Park, OH The fourth edition PDF Race car performance depends on elements such as the engine, tires, suspension, road, Key Words.
Title Assessing aerodynamic performance in Drag reduction of a car model by linear genetic programming control ; Sep 8, Drag reduction of road vehicles has become a cornerstone challenge due to the in Key words: unsteady flows, flaps, airbrakes In other words, taper at There are no words to describe the support that they have A brief, descriptive project title words.
Download 18MB - University of Glasgow ; The aerodynamics is a very important aspect in the design of road vehicles, particularly after two Hucho and Sovran reported that a blockage ratio of. ISBN , Skip to content. Aerodynamics of Road Vehicles details the aerodynamics of passenger cars, commercial vehicles, sports cars, and race cars; their external flow Hucho ed , , , Society of Automative Aerodynamics of road vehicles hucho - downloadhq.
Wolf-Heinrich Hucho. Publisher: Elsevier. View: Aerodynamics of Road Vehicles details the aerodynamics of passenger cars, commercial vehicles, sports cars, and race cars; their Automobile Body. Search Search. Vehicle Aerodynamics: Aerodynamic drag and its types and various forces and moments, its effects HuchoAerodynamics of Road Vehicles 4th ed.
Iaccarino, R. VerziccoImmersed boundary technique for turbulent flow simulations. Since the air flow is generally 'attached', the calculation can be accomplished in two steps.
First the non-viscous flow field is determined; then the effect of viscosity is calculated from 'boundary layer' theory. The theoretical methods upon which this procedure is based have been developed continuously and have been expanded to include other requirements such as those resulting from higher flying speeds Mach-number effects.
The flow field around a car cannot be treated in the same way, for two reasons. From Figs 1. The effect of viscosity is no longer confined to comparatively small zones close to the surface of the body boundary layer. Furthermore, with a car it is not possible to distinguish several more or less independent flow fields. The flow field around a car body has to be treated as a whole. Chapter 13 summarizes the present state of numerical methods in car aerodynamics. These methods may be used to guide the work in the wind tunnel.
However, much of the aerodynamic design of a car is to prevent, or to tune, separation. The only way to do this is through experimentation. Scope 9 Building aerodynamics addresses a number of similar objectives: Useful reference material includes Hoerner1 2 wind forces on build- ings , Ackeret1 3 significant problems of building aerodynamics, based on clear examples , Sachs 1A presentation of the current state of knowledge , and construction aerodynamics in condensed form by Houghton and Carruthers.
The primary difference results from coupling of individual cars into long trains, which produces a very long body in comparison to its height and width. Special relationships result when trains meet one another, due to the small gap between the tracks, as well as when driving into tunnels and driving through very narrow tunnels.
The primary development goals for railway aerodynamics are: In contrast to the development of road vehicles, for which the trend to higher driving speeds has virtually vanished with the exception of racing cars, speeds are still being increased in the railway sector. For this reason aerodynamics is becoming increasingly significant in this branch of transportation technology.
Some early data on the resistance of trains is given by Hoerner. The aerodynamic drag of a water-displacing ship is small in comparison to its water resistance, but not so for fast hydroplanes, hydrofoils and hovercraft. The aerodynamics of a surface ship include the lateral force in addition to the resistance, which is of particular concern for ships with high superstructures, such as ferries, when docking.
On the other hand, the flow of air around the funnel is a prime concern for passenger ships. The aerodynamics of the sail have many problems in common with wings. As for trains, naval architects depend upon individual publications, there being no comprehensive work on this subject.
Data on the aerodynamic drag are given by Hoerner. Gould1 n His work also includes information on simulation of the water surface and of the air boundary layer over the water surface in a wind tunnel. There are also parallels in other disciplines on the flow inside the vehicles.
The flow of air through the radiator in a car is comparable to the flow of air through the water or oil cooler in an aircraft. The counterpart of the climatization of the passenger compartment is room climatization in buildings see Chapter Historical development 11 Initial development concentrated exclusively on drag, and the problem of cross-wind sensitivity only arose with increasing driving speeds.
Lately attempts have been made, by suitable shaping, to eliminate the deposition of dirt and water on the windows and lights. The following brief history is based upon available literature. Early numerical data, particularly drag coefficients, must be considered very unreliable.
Drag coefficient was sometimes measured on test vehicles through coast-down tests, or by measuring the top speed, both of which can lead to errors see Chapter Most measured data, however, came from wind tunnel tests on models of varying quality and scale.
Nor were the techniques for representation of the roadway uniform, so that, as indicated in Chapter 11, the absolute accuracy of the data is low and the comparability of data from different authors is uncertain. This brief account of the history of automobile aerodynamics has two aims.
The first is to show which work contributed to the development of automobile aerodynamics; the second illustrates how this knowledge was applied to autornobile design. Developments up to are described by Koenig-Fachsenfeld.
They were little suited to the automobile, for instance the 'airship form', or ineffective, for instance the 'boat tail'. Due to the poor roads and low engine power, speeds were still so low that aerodynamic drag only played a subordinate role. Most cars derived from these basic shapes had one error in common: In spite of this, shapes represented great progress toward lower drag in comparison to shapes based on the horse-drawn carriage.
Jenatzy's record-breaking car was the predecessor of all single-seat race cars, even though the body of the car was still positioned above rather than between, the wheels. Historical development 13 Alfa Romeo from The length to height ratio for this body is approximately 3.
Similar designs existed in which the wheels were partly enclosed by the body design by O. Bergmann, refs 1. The attempt to design a car with an integrated ideal' body was repeated several times, but without production success. In contrast to the shapes shown in Figs 1. The flow, separating at the front and from the fenders, will not re-attach because of 'boat tailing' the rear end. The boat tail, which was applied in different variants on mass-production limousines and sports cars, is an example of how aerodynamic arguments are often misused to justify stylistic curiosities.
The more Prandtl and Eiffel worked out the nature of aerodynamic drag, the more this knowledge was used to explain the aerodynamic drag of cars; see for instance Aston. Buchheim in the large wind tunnel of Volkswagen AG, After the First World War, the design of streamlined bodies started at a number of locations simultaneously.
Rumpler, who had become well known through his successful aircraft, the 'Rumpler-Taube', developed several vehicles which he designated 'teardrop cars'. The most famous Rumpler limousine is shown in Fig. In order to make use of the narrow space in the rear of the vehicle, Rumpler decided on a rear engine configuration.
Viewed from the top, his car has the shape of an aerofoil. But the roof is also well streamlined, thus proving that Rumpler was aware of the three-dimensional character of the flow field Fig. Details are to be found in papers by Heller,1 23 Eppinger1 24 and Rumpler himself. On the Rumpler car this increase in drag must have been at least 50 per cent, as measurements performed by Klemperer 1 2 6 as early as show.
The car entered in the Strassburg Grand Prix by Bugatti in was developed primarily according to two-dimensional theory Fig. As on modern championship race cars, the air flow below the car is controlled as much as possible by extending the body downward. The arched shape also facilitates enclosure of the wheels. However, the flow over the tail must have been disturbed considerably by the driver. The three-dimensional flow around a bluff body in the vicinity of the ground was originally analysed by P.
Jaray recognized that the flow around a body of revolution, which has a very low drag coefficient in free air, is no longer axially symmetrical when close to the ground. As a result the drag increases, owing to the flow separation occurring at the rear upper side.
At Historical development 15 the limit, where the ground clearance approaches zero, the optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image—produced through reflection from the roadway.
This half-body, which had a ratio of length to height of 4, was modified by Jaray so that the mid-section formed a rectangular cross-section with rounded upper corners.
Drag Reduction of Passenger Car Using Add-On Devices
Wind tunnel tests performed by Klemperer1 26 at Jaray's request showed that the drag of this half-body increased with increasing ground clearance, due to the air flow around the sharp lower edge; by rounding off these edges it was possible to eliminate this increase Fig.
Jaray then attempted to approximate the shape of this half-body by assembling individual aerodynamically shaped bodies. The half-body itself, as will be illustrated later, was used again and again by a number of designers. Klemperer, , see ref 1. Jaray schematic Figure 1. In both examples the basic body is formed by a profile segment. On the first, a second profile is attached vertically, and in the second example half of a body of revolution serves as the upper part.
This body, later called the 'combination form', was based With a rear end in the shape of a half-body this can be achieved only with a very long, slender tail. In the combination form, the tapering of the rear end is subdivided into two planes to prevent excessive pressure increase, which could result in separation. Unfortunately Jaray1 29 published only a 'schematic' pressure distribution for a combination form.
Wool-tuft pictures for Jaray cars indicate that separation can be prevented only for extremely slender versions of the combination form. In Jaray made up a table of types in which he illustrated the large variety of shaping possibilities according to aerodynamic aspects; see for instance ref. The characteristic of all of his designs was the relatively sharp horizontal rear edge.
This approach did not prove particularly practical for road vehicles. The most important of Klemperer's measurements on models of the first Jaray cars are summarized in Fig. On the other hand, Klemperer's early measurements clearly show that the drag coefficient of Jaray's combination form of 0. Chapter 4 shows how modern automobile aerodynamics uses this potential—first published by Jaray and Klemperer in As can be seen from Fig.
Their shape was too Figure 1. Kleyer courtesy Frhr. Koenig-Fachsenfeld Historical development 17 revolutionary, but also Jaray adhered too closely to his basic principles. The prototypes built for the various makes all looked alike. As more high-speed highways were constructed cars of streamlined shape became very popular until World War Two ended the era of Jaray cars.
One mass produced Jaray-style car was the Tatra 87 of , designed by H. Ledwinka Fig. Ledwinka Adler Trumpf, and by placing the engine at the rear end it was possible to locate the passenger compartment further forward, where more space was available.
A body shape was developed which consisted of a horizontal basic Figure 1. As with all Jaray shapes, this second profile was also rounded at the front from the top view.
The resulting shape is known as the 'Lange car'. A drag coefficient of 0. Measurements performed by the author and his co-workers on a one-fifth scale model approximately confirmed this value with 0. However, the model lacked details such as running gear, wheel wells or window recesses. Approximately the same low drag coefficient can be achieved with the Lange shape as with half-body shapes Fig. The Porsche has a shape similar to that of the Lange car.
The relatively large llh necessary for a Jaray-shape prevented the success of Jaray's idea, though numerous pseudo-Jaray shapes, called fastbacks, were built, such as the Chrysler Airflow and the Volkswagen Beetle.
As will be shown in Chapter 4, this shape, with its steep-sloping rear end, produces two distinct longitudinal vortices. Due to the downwash induced by these trailing vortices, the flow along the longitudinal mid-section of the car remains attached over a long path; however, a high vortex-induced drag is produced so that the total drag is higher than for true Jaray shapes.
In comparison to the box-shaped bodies with drag coefficients between 0. An approach similar to that of Jaray was pursued in France by Mauboussin1 32 in His car, the Mistral, had the shape of an aerofoil in plan—the rear ending in a vertical knife edge.
The rear wheels were covered by a horizontal profile, producing an intersection at the rear similar to the Jaray shape. However, the slender taper of the body greatly limited the internal space. However, Jaray's attempt to approach this limit as closely as possible with his combination form led to impractical shapes, and his work provided no indication of the way in which the typical drag of automobiles of the s around 0. However, Lay working at Michigan University in the early s started to close this gap.
By systematically modifying the shape of the car at the front and the rear, Lay isolated the individual aerodynamic effects Fig. His investigations revealed the strong interaction between the flow fields of the car's fore-body and rear end.
The low drag of a long-tail model was maintained only when the flow around the fore-body was well attached. The drag increased significantly when the flow separated at the steep windscreen. On the other hand, if the drag was already high due to the blunt rear end the drag increase from a steep windscreen was only moderate.
Unfortunately Lay's model, which could be built up from segments, had parallel side walls and sharp corners, which resulted in a fairly high drag and limited the significance of his findings. The most important result of Lay's work was that a blunt rear end resulted in only a relatively small increase in drag in comparison to a long tapered rear end.
Similar findings were made by Dornier as early as Historical development 19 Figure 1. From , the blunt rear end shape which first occurred in the work of Lay led to the development of the 'Kamm-back', which combined the advantage of greater headroom in the back seat with that of low drag.
The Kamm-back, the Lay blunt back and Klemperer's long-tail design are compared in Fig. Kamm S. Klemperer's long tail ] and the blunt rear ends of W.
Kamm attached for as long as possible and is then forced to separate by cutting off the rear end at an already much diminished cross-sectional area. This results in a small wake. By tapering the body moderately, the flow is subjected to a pressure increase which ensures that the pressure at the rear of the vehicle, the 'base pressure', is comparatively high, which itself then reduces the overall drag.
Kamm proposed this idea in a paper published in , but presented no practical design, referring only to the earlier work of Klemperer and Lay. Koenig-Fachsenfeld must be credited with the invention of the cut-off rear end, and his published measurements on bus models in '35 clearly proved its advantages see section 1. Despite this, the cut-off rear end became known as the 'Kamm-back' sometimes called K-back.
Much later Everling1 36 claimed that he was the first to recognize the advantage of the cut-off rear end in , when he had designed a bus with a cut-off tail. In the first passenger vehicle with a Kamm rear end, the Everling car, was built Fig. Kamm went on to build Figure 1. The advantage of the Kamm-back, in comparison with other aerodynamic designs, can be clearly seen in Fig. The drag coefficients published for the Everling and Kamm cars indicate a high degree of scatter Table 1.
Historical development 21 Table 1. Everling and W. Although vehicle aerodynamics initially concentrated on the drag in still air conditions symmetrical oncoming flow , the problems of side wind as well as cooling and ventilation soon became apparent, as noted by Klemperer,1 26 whose results Fig.
Klemperer1 26 increasing yaw angle for 'sharp edged' cars which already had high aerodynamic drag, but decreased sharply—after a slight increase—with streamlined shapes.
He stated: However, he made no measurements of lateral force and yawing moment, the most significant in cross-wind sensitivity. The drag curve for cross-wind will be examined in detail in Chapters 4 and 8, which also show that Fig. Large angles of yaw, at which Klemperer's 'sail-effect' becomes effective, occur in practice only at low driving speeds, at which drag is insignificant anyway.
On the other hand, at small angles of yaw additional resistances occur, which are considerably higher than might be deduced from Fig. It was eventually discovered that only vehicles with long, tapering rear ends suffered in this respect, while the yawing of vehicles with truncated rear ends Kamm back was not uncommonly high see Chapter 5.
It was even possible to produce aerodynamically stable yawing moment characteristics by adding tail fins, the effectiveness of which was proved in driving tests by Sawatzki. False fins were sometimes used as styling elements, but even the rather large fin on the Tatra 87 Fig. The danger from cross-winds results primarily from gusts, which occur naturally but are also caused by the terrain as well as the presence of vegetation and buildings, as originally reported by Huber.
However, little thought has been given to reducing cross-winds by proper landscaping, although the barriers and walls constructed to protect the environment from road noise may provide wind protection as well.
Special attention has to be paid to gaps in these barriers and walls; see section 5. With the start of systematic work on automobile aerodynamics, the problems of the flow of air through the vehicle were examined. Klemperer1 26 considered the air flow through the cooling system in his model tests and showed that air flow through the radiator increases vehicle drag. Fiedler and Kamm1,42 suggested ways of reducing this drag increase. In Kamm's school the flow processes in the radiator were examined in detail.
The interaction between the vehicle, radiator and cooling air fan was investigated by Schmitt and Eckert. Much later see Chapter 10 , the possibility of improving passenger comfort by properly shaping the pattern of the internal flow field was investigated.
As mentioned earlier, true aerodynamically designed 'streamlined shapes' were used only sporadically for mass produced automobiles.
The findings of Jaray, Lay, Everling and Kamm were applied, but their potential was not really exploited. Nevertheless, even at a very early date there were attempts to achieve even lower drag following the ideas of Klemperer and his 'half-body shapes'. As early as Persu1,45 built a car in Berlin which was derived from a half-body. The engine was located in the tapering rear end.
No test results have been found for this vehicle. From several American authors worked with half-body cars, but their work was confined to the model stage. To evaluate the results achieved on the models with varying perfection and different scales, each half-body shape is compared with a contemporary limousine model tested by the same author. With the exception of the extremely long rear end examined by Lay, all half-body models had a drag coefficient approximately one-third of that of the contemporary limousine.
Fishleigh M 1: Heald 1: Lay 1: An analysis of theflowaround the Lange car Fig.
hucho aerodynamics of road vehicles pdf writer
The Figure 1. The most important test results for this vehicle and scale models are given in Fig. The drag coefficient cD is plotted against the ground clearance e, which is made non-dimensional with the height h of the vehicle. With high ground clearance, the half-body had lower drag than the profile from which it was derived.
With decreasing ground clearance, the drag 0. Historical development 25 lock-to-lock clearance of the completely covered front wheels. The large frontal area must therefore be considered intrinsic to this design. The development of streamlined automobiles was interrupted by the Second World War.
Citroen and Panhard were the only car manufacturers resuming this development after the war, as can be seen from Fig. While Jaray's ideas can still be recognized on the ID 19 body basic body and attached profile the GS and the CX are more closely related to Kamm's ideas cut-off rear end.
All three models have an extremely low drag coefficient in comparison to their contemporary competitors. The A Model year A [m2 ] 1. In the area of sports cars, Porsche, above all, has paid consistent attention to aerodynamic design, as can be recognized from the model series in Fig. While the older models A and B can be called Jaray shapes, the is more closely related to the Lange model; see Fig. The newer models from Porsche, the , and , also have a distant relationship to the Lange shape.
In the course of styling a new model, the aerodynamicist is frequently confronted with a question like, 'What happens with drag if one or other detail of the body is changed?
He selected nine body parameters crucial to theflowpattern around a car, and thus decisive for its drag; see Fig. Each is rated with regard to its aerodynamic quality. The sum of points corresponds to the drag coefficient: Historical development 27 due to the cooling air flow. Therefore White's rating method is not appropriate to differentiate today's cars with regard to their drag, not least because low-drag cars, which are coming into production more and more, were not around when White established his rating method.
The merit of the method, however, was to identify clearly those areas of a car which have a major influence on drag, and to make them known to people in the car business who have no experience in aerodynamics. Previously, ways were found of adapting aerodynamics to practical automotive engineering requirements of styling, packaging, safety, comfort and production. The method of optimizing body details developed by Hucho, Janssen and Emmelmann 13 represents one approach.
This 'third phase' is character- ized in Fig. Since this method is treated in detail in section 4. The starting point for aerodynamic development is the stylistic design; modifications to the shape must be made within the styling concept.
Details such as radii, curvature, taper, spoilers etc. Historical development 29 reductions in the drag can be achieved in this manner Fig. Using the technique described, it was possible to reduce the drag coefficient of a VW Scirocco I from 0.
In spite of the emphatic 'hard' styling, it was possible to achieve the same drag coefficient as the Opel GT, which was styled according to the principles of streamlining. One such method is 'interactive shape optimization', which permits significant deviations from the original styling concept; see section 4.
The other is to start from a body of extremely low drag, and to convert this into a real car with low drag. This low-drag configuration is converted into a real car step by step, applying the optimization technique for each detail. This method has been elaborated by the author and his co-workers and is outlined in Fig.
Prior to the construction of the Autobahn, autostrada, motorway and highway, mass transport of goods and people was accomplished by rail. The first buses and trucks were designed like elongated passenger cars. The same aerodynamic design principles were applied: Kieselbach1 19 recorded this period with many photographs and design drawings. With the introduction of the 'tram-bus' by Gaubschat in , the shape of buses broke away from cars.
With the engine underneath the floor—or later at the rear—more seats could be placed within the same overall length. The front end of the tram-bus was extremely well rounded Fig. Gaubschat on a Bussing chassis, courtesy RJ. Kieselbach By Pawlowski1 52 had published data on the influence of leading edge radii on the drag of rectangular bodies.
Although this result was confirmed by Lay in with road tests, and although this finding has been repeated several times see Chapters 8 and 11 , it was not applied for a long time. In the Kamm-back was introduced to bus design, based on measurements from Koenig-Fachsenfeld. The two reasons for the wide recognition given to this work, apart from the drastic drag reduction, were the unique market position long held by this van all over the world, and the reference made by H.
Schlichting in his famous book Boundary Layer Theory. However, for the first Volkswagen van no use was made of the earlier work of Pawlowski. The front end of the first VW van was much more rounded than was necessary to achieve an attached flow and the related low drag. Palowski, Figure 1. The basic work was done on a quarter-scale model in Owing to the long lead time of this vehicle, these data were not published—together with full-scale measurements—until see ref.
The smoke trails taken on a full-scale vehicle Fig. Today leading-edge radii of buses and cabs of trucks, sometimes even those of trailers, are optimized in the same way; see Chapter 8. The idea of guiding the flow by vanes goes back to the work which Frey published as early as Guide vanes have long been applied to steam locomotives, mainly to keep the smoke away from the driver's cab, but also to reduce drag. The big advantage of this spoiler, and others, is that it can be attached to trucks already on the road.
It also allows for individual matching to various trailer configurations.
The size of the engine and drive train, the space available for the passengers and the volume of the trunk boot largely determine the primary dimensions shown in Fig. The 'down-sizing' programme of the US auto industry has brought US cars closer to European dimensions. Nevertheless, the main proportions of the body shapes vary little Fig. In the smaller class, e. On the latter, significant differences in the slant angle of the rear end are present for more detail see Chapter 4.
Aerodynamics of road vehicles HUCHO.pdf
The middle range, e. Station wagons are not considered here. The larger passenger cars such as the Mercedes W or Audi Fig. Development trends 35 Figure 1. According to ref. The vehicles in all weight classes converge to practically the same height dimension; however, the ergonomic limit now seems to have been reached.
For very small cars—the minis—the height is How height is traded off against length has been demonstrated by Costelli1 61 for the Fiat Uno car. In automobile aerodynamics the frontal area A, which was defined in Fig. In the future the slope of the line A versus m shown in Fig. While the frontal area A can be assumed to be constant as a comfort dimension for the individual car classes, the kerb weight will be reduced further.
Among the various cars there is little variation in cross-sectional shape. Car designers have cut off from the rectangle what was not needed for the passengers' comfort see hatched area in Fig. Among the different car classes, the frontal area of cars from competing manufacturers is almost identical. This again confirms that the frontal area is well suited to characterize the size of a car for aerodynamic purposes.
In Fig. Despite the fact that there are speed limits in most industrial countries with the exception of unlimited top speed on the German Autobahn top speeds are still increasing. The speeds technically obtainable have progressed far beyond the top and average speeds driven in road traffic and even in racing.
However, a relationship between speed records and the practical requirements of automotive engineering is no longer valid see also section 7. Owing to the lack of statistical data only a general tendency can be outlined. In the first, the period between the two World Wars, the cars were stretched and body details were rounded while maintaining significant characteristics such as projecting fenders and headlights.
In addition to a lower drag coefficient of approximately 0. The second stage in the reduction of drag was reached with the introduction of the pontoon body with its variants, the notchback, fastback and squareback. By incorporating the fenders and headlights in a closed body shape, it was possible to improve significantly the flow of air around Using this design, drag coefficients of 0.
This scatter range has remained unchanged since about However, it is difficult to determine whether the reduction in drag resulted from the influence of aerodynamics, from styling or from more advanced manufacturing techniques.
The recent past is illustrated in Fig. The histograms, from ref. From these data, the average drag coefficient has been calculated and plotted against time. These data are comparable in that they are all derived from measurements carried out in the Volkswagen wind tunnel.
The average drag coefficient began to drop in The range of data—the scatter—is still enormous. Even some contemporary cars have drag coefficients worse than 0.
With concept cars see section 4. Dragfiguresof 0. Klemperer's value of 0. Today a drag coefficient of 0. In the long run 0. Increasing fuel prices will also encourage aerodynamic development of commercial vehicles. Drag coefficients for box vans cover the range of 0. A value of 0.
Today the drag coefficients for heavy trucks lie between 0. Considerable drag reduction can be achieved through the design of the cab and the use of air deflectors.
In early times, most of the aerodynamic AlldatafromVW measurements Year 0. Development trends 41 work was done by experts from outside the car industry, with experience in fluid mechanics on aircraft aerodynamics but with little understanding of the automobile.
Most of their suggestions were too advanced for their time and were therefore not considered. And even Jaray, whose ideas were much closer to the automobile, had little success because of his unwillingness to interact with the stylists. All his cars looked alike, which is just what the stylist does not want. On the other hand, stylists used, and sometimes misused, aerodynamic 'devices' as marketing gimmicks.
The boat tail, fastback and tailfins are examples. This situation started to change when the car makers began to carry out aerodynamic development in their own purpose-built wind tunnels. The aerodynamicist, now an employee, became an automobile engineer and had to interact with design.
He became aware that the demands of aerodynamics did not ease the task of the stylist, who already had many technical restraints and legal requirements to observe. The stylist, however, discovered that aerodynamics could set trends more logically and reasonably than did fashion, and began to accept this trend as valid for design criteria. The trend of drag coefficient against time shown in Figs 1. Development trends 43 c Figure 1.Klemperer1 26 considered the air flow through the cooling system in his model tests and showed that air flow through the radiator increases vehicle drag.
In order to make use of the narrow space in the rear of the vehicle, Rumpler decided on a rear engine configuration. Includes index. Influence of moving belt dimensions on vehicle aerodynamic forces.
In the simple case of Fig. The importance of aerodynamic design has been discussed earlier. In case of bluff bodies the pressure drag is prominent.