DE3213000A1 - Vehicle body with good aerodynamic properties - Google Patents

Abstract

A vehicle body with good aerodynamic properties, in particular for passenger cars, is proposed, which body has a passenger cell (13) which has an approximately rectangular cross-section and has at least one windscreen (11) arranged at an incline. In order to decrease drag, the vertical change in the cross-sections of the vehicle body is assigned such a change in width in the longitudinal direction that edges are only flowed around (tranverse flow of the upper longitudinal edge of the vehicle) to a small extent without the flow being broken up or such a flow occurs without substantial breaking up. <IMAGE>

Description

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The invention relates to an aerodynamically favorable body for vehicles, in particular for passenger cars, of the type specified in the preamble of claim 1.

The body of such vehicles should have the smallest possible drag coefficient (c value). At the same time

However, there are still further requirements to be made of a usable body, such as sensitivity to crosswinds (Lateral force and yaw moment) and the lift should also be as low as possible. Furthermore, the body should be at low The frontal area and short length offer sufficient space and good visibility to the front and rear.

In today's passenger cars, the pontoon shape with different rear shapes such as notchback, Hatchback, box rear and beveled box rear largely prevailed. With pontoon-shaped cars and the With the usual stern shapes, drag coefficients of the order of magnitude of about 0.4 are achieved. It is known the drag coefficient further downsizing through various measures. B. by strong inclination of the front and Rear window, by rounding off all edges and avoiding protrusions and recesses, lower the resistance further. Even by bringing the body closer to a teardrop-shaped streamlined body, although its shape deviates from the usual rotationally symmetrical teardrop shape because of the presence of the ground, one can derive the drag coefficient lower it further. This measure! however, they also have disadvantages which prevent them from being used. So z. B. increase sensitivity to crosswinds and lift. By inclined discs you can the visibility deteriorate sharply and at the same time the solar radiation increases sharply, so that the passenger cell is heated up unreasonably. With the described Measures can also be taken to increase the length of the vehicle, which is sometimes undesirable. Closing

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Can also be borrowed, especially with a teardrop-shaped body the frontal area of the vehicle increase, which also means an increase in resistance, although this is reflected in the C "value not noticeable.

The resistance of a vehicle is made up of two parts, among other things. The resistance is on the one hand by the The idealized basic shape of the body is determined and, on the other hand, through various attachments and jumps on the body determined, for example, by the wheels, the wheel arches, the bumpers, exhaust system, exterior mirrors, gutters, etc. The invention relates to the proportion of the resistance that results from the idealized basic form.

The invention is based on the object of showing a body of the type described above that is favorable in terms of flow, whose idealized basic shape has the lowest possible resistance, in order to reduce the total resistance to lower such vehicles.

According to the invention this is achieved in that before and / or after the passenger compartment of the change in height of the body cross-sections in the longitudinal direction such a change in width of these cross-sections is assigned that only a small one Flow around the edge (transverse flow around the upper longitudinal edge of the vehicle) occurs without flow separation or without substantial separation. The invention is based on what is known per se Fact that relatively large air flows around the edges Flow detachments and vortex formation occur where the height of the body cross-section changes quickly in the longitudinal direction changes while the width remains approximately constant. With the body shapes customary today, this occurs particularly in the area the. Front window and in the area of the rear window. According to the present invention, only a small flow around the edges should be be allowed without detachment or without substantial detachment, thereby significantly reducing the resistance

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will. Since the flow around the edges is not disadvantageous per se, in particular not when it is in contact with the body, such a flow around the edges can certainly be permitted within certain limits; it only has to be kept within such limits that a substantial flow separation does not occur. By increasing and decreasing the width accordingly, it is possible to create a shape in which the lateral flow around the pberen.-vehicle edges is completely avoided. However, this leads to body shapes that are unfavorable in other respects and are therefore less suitable for practical use. It is therefore necessary to make certain compromises, i.e. to allow certain flow around the edges without significant flow separation and nevertheless to act according to the basic concept. Theoretical calculations and .Experimente show that z \ ir complete avoidance of Kantenuiuströmung a considerable enlargement of the width in the portion of the panel and a corresponding reduction in the area of the rear window is required. This leads to body shapes which, in the area of the passenger cell, provide a 'comparable amount of space as the usual shapes, but which are otherwise unfavorable, in particular with regard to the track width in the area of the front wheels. To avoid these disadvantages, the change in width in the area of the front and / or rear window is made weaker than would be necessary to completely avoid the flow around the edges.

In the case of a passenger compartment with a height-to-width ratio of about 1: 1.2 to 1.3 can result in a lateral widening of the body in the area of the windshield by about 50 to 150 Percentage of the change in height must be provided in the area of the windshield. A corresponding reduction in width results in the area of the rear window. . -

The body can rapidly increase in width in the area of the inclined windshield and in the area of the passenger cell have substantially constant height and width. You can in the area of the adjoining the passenger compartment Rear end towards the body end have decreasing height and decreasing width in order to as well here a 'as small as possible flow around the edge without substantial To achieve flow separation. The decrease in height and width at the rear end is intended to be gradual be, preferably with angles ranging from about 15 ° to 20 ° in order to avoid the normal flow separation here too, even with complete avoidance of any flow around edges due to rapid changes in height and width and the associated pressure increase can occur.

To achieve a large track width in the area of the front wheels the body can be constricted in the transition area between the front part and the windshield the width. This constriction must, of course, be so gradual that there is no separation of the current takes place, and that the part of the constriction which results in an increase in the width of the vehicle, for example in the area of the windshield, is arranged. So as not to cause any additional flow around the lower longitudinal edge of the vehicle, and the basic concept To be used wherever possible where it is of considerable benefit, the constriction is essentially provided in the upper area and arranged tapering in the direction of the floor panel. This is at the top of the vehicle, i.e. in the direction of the ~ Area of the windshield that has a significant effect, while the vehicle is down in the area of the floor panel has a constant width between the front part into the passenger compartment. :

In the case of a flat design of the floor panel, i.e. the vehicle floor, In the area of the front and rear windows, there is also a flow around the lower one because of the changes in cross-section Edges of the vehicle, which is weakened by the presence of the ground or the road. One can counteract this flow around the ground by decreasing in the area in front of the windshield and in the area of the Front windshield increases again. These changes in cross-section are, however, much smaller than those described above lateral cross-section changes. So on the floor panel, in the transition area between the front part and the windshield a drawn-in dent can be provided, the greatest constriction of which is approximately at the beginning of the windshield is arranged.

The corners of the body cross-sections can, in the area of strong cross-section changes, permit flow around the edges be formed strongly rounded without significant flow separation. This is especially true for such cases in where a relatively small change in width is selected, and thus a relatively large flow around the edges and possibly even a weak separation with correspondingly weak vortex formation and increased drag is permitted.

The basic idea of the invention has already been realized when the width of the body in front of the windshield is less than behind the windshield. The advantages of the invention lie in the fact that the resistance of the idealized basic shape is made very small, without the front pane too must be placed at an angle, and without the passenger compartment having to change its shape significantly. Also the length of the vehicle does not become excessively large. Crosswind sensitivity and Buoyancy remains low.

The "invention" is further based on a few exemplary embodiments explained and described. Show it:

1 shows a schematic rectangular body cross-section with the representation of a flow separation

2 shows the representation of the flow problem on the body • rie cross section and on a mirror image,

3 shows the representation of an auxiliary cross-section summarizing the cross-section and the mirror image,

4a, 4b, side view, front view and top view of a-4c Double model of a body shape in which the flow around the edges is practically avoided ',

5 shows a diagram of the tangential force coefficient over the sliding angle for a body shape from the state the technology and according to Fig. 4,

6a, 6b, side view, front view and top view of a 6c second embodiment of a double model of a Body,

7a, 7b, side view, front view and top view of a 7c body in a further embodiment and

8a, 8b, side view, front view and top view of a 8c body in a further embodiment.

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The emergence of the flow around the edges, which increases the drag coefficient with flow separation is explained with reference to FIG. 1. It is a body cross section 1 in a rectangular shape shown in an idealized manner over a street 2. Normal to the cross-section of the body when the air flows around the body 1 there occurs a displacement flow where the height of the cross section changes very sharply, i.e. essentially in the area of the windscreen and the rear window. This causes the flow to move around the upper longitudinal edges 3 to flow around, namely in the areas of the side wall 4 of the body cross-section 1. It releases the flow from the longitudinal edge 3 and forms a separating surface that rolls up to form a vortex 5. In Fig. 1 is the so-called cross-flow for the flow in the area of the windshield shown, that is the flow in a cross-sectional plane, which arises when looking at each point of the plane the component of the flow vector falling into the plane assigns. Especially with rapid changes in the height of the cross-sectional area and not very strongly rounded or The described spatial detachment occurs even in sharp-edged corners, with the corresponding separating surface rolls up into a vertebra 5. It goes without saying that in the area of the rear window, under the decrease in height there is a Flow around the longitudinal edges 3 in the opposite direction with a corresponding Vortex formation occurs.

By assigning a corresponding change in width to the respective change in height should be achieved that mar a small flow around the edges without separation of the flow or one with only insignificant separation occurs. Around In order to be able to carry out this design, it is necessary, with a given change in height of the cross-section, the required Determine the change in width. The idealized body shape should be calculated at least approximately will. Because of the complexity of the flow process is an exact calculation of the flow field taking into account ^ -

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Viewing the boundary layers, the vortices 5 described and the dead water is not possible according to current knowledge. For approximate calculations one can first use the concept of the so-called "Slender body" theory, which states that if the cross-section changes on slender bodies in the longitudinal direction are not too rapid, the cross-flow only occurs from the respective one Cross-section and its rate of change in the longitudinal direction depends and not on the other dimensions of the Body. For a first look, it is sufficient to view all body cross-sections as exact rectangles. It will then If the friction is also neglected, the theoretical potential shown in FIG. 2 results for the cross flow plane flow problem. It occurs at the edges of the rectangle or the body cross-section 1 on all four sides with a constant normal component in each case a flow. from, where the amount of the respective normal component is proportional to the corresponding change in the rectangular cross-sectional shape is in the longitudinal direction of the vehicle. With a level vehicle floor or if the width did not change in the longitudinal direction, the normal component would therefore be on the underside or on the side surfaces equals zero. In addition, the normal component of the flow on the road indicated in FIG. 2 must disappear. This condition can be replaced by a cross-sectional area mirrored on the road with the same Arranges flow conditions as mirror image 6. With an arbitrarily chosen intensity of the constant normal component on the four sides there is a flow around the corners of the cross-sectional area up at infinitely high speeds. In particular, there is a strong flow around the corners when the cross-section only changes in one direction. In the case of a real flow, this flow around the corner (cross flow) to an exiting vortex surface that rolls up into a vortex. To counteract such eddies, one must such change in cross-section of the. Body cross-section found at which the corner numbers noise as small as possible is or at least so large that koine or only one un- "

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substantial flow separation occurs. To this one brings on the sides of the cross-section and the mirror image 6 such a source distribution that from this the desired Normal component distribution emerges and at the same time the flow around corners is avoided or only a desired one Possesses intensity. This task can no longer be solved analytically. A solution can only be found numerically Found with the help of a two-dimensional panel process will. To further idealize the problem without the essential flow processes in the upper part of the vehicle can significantly influence the side wall 4 of the Cross-section or the vehicle can be thought of being pulled down to the street, i.e. a vehicle is created with a Ground clearance zero, so that the potential described above would result in the illustration of the problem according to FIG. 3 reduced. This results in a rectangle consisting of the Body cross section 1 and the mirror image 6, on its Top and bottom the flow exits with the same constant normal speed and on its sides with a other constant normal speed exits. The ratio of the two normal speeds must be determined in which there is no flow around the corner. Obviously this speed ratio depends only on the aspect ratio of the Rectangle. The above-described panel procedure or the method of the conformal mapping can be used, whereby the rectangle is mapped on a half-plane and the flow conditions in the image plane are met. With the help of this procedure one can in the given by the "Slender body" theory Approximation, design body shapes so that there is no flow around them the edges occur or only those with the desired intensity " sity. By choosing a suitable edge rounding one can then achieve that no or only an insignificant separation occurs. For body shapes with a height that is common today

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The result is a width ratio of about 1: 1.2 to 1.3 lateral widening of the body in the area of the windshield of about 50 to 150 percent of the change in height in the area of the windshield.

To examine the question of the extent to which the invention is based Concept is also correct, the following experiment was carried out. On a model of a normal today Body shape with notchback and an.a comparison model with a body shape according to the invention, were in the wind tunnel Three-component force measurements carried out. The comparison model was designed so that there was no flow around the edges occurred. The rate rounding was the same as in the normal model. Both models were examined as so-called double models in the wind tunnel. FIGS. 4a, 4b, 4c show the side view (FIG. 4a), the front view (FIG. 4b) and the top view (FIG. 4c) of the comparison model with the front part 10, the windshield 11 and the rear 12. In the two models tested in the wind tunnel, the the same end face of the front part 10 and a passenger compartment 13 of the same size are observed. Both models were the same length.

FIG. 5 now shows a diagram of the coefficient of the tangential force (Cm, which at ß = 0 corresponds to the C "value) the results for a normal body shape over the sliding angle ß, in solid lines and for the body shape of the comparison model according to FIGS. 4a, 4b, 4c according to the dashed line Line management. The tangential force coefficient is above the slip angle ß (influence of crosswinds) for two different approach velocities plotted, surprisingly, is the resistance value the new body shape according to FIGS. 4a, 4b, 4c only about a fifth as large as that of the normal shape. The increase in the tangential force coefficient with the sliding angle ß is also much smaller than with a normal shape, so that 'the drag advantage is maintained even in cross winds. The side force is

in the new body is roughly halved, while the yaw moment (based on a point in the center of the vehicle) is is about the same in both forms.

However, one can also see the disadvantages in the model according to FIGS. 4a, 4b, 4c. In the area of the front part 10 only results a relatively small track width for the front wheels. Here compromises must certainly be made in such a way, that a certain flow around the edges is allowed, which is dimensioned so that no or only a slight separation occurs, which increases the drag coefficient only comparatively little. FIGS. 6a, 6b, 6c again show such a shape on the basis of a double model in side view (Fig. 6a) ', front view (Fig. 6b) and top view (Fig. 6c). When comparing the double model according to FIGS. 6a, 6b, 6c with that according to FIGS. 4a, 4b, 4c it is noticeable that the track width in the area of the front axle has already been selected to be larger. According to the now approved In the flow around the edges, the rounding of the edges was chosen to be somewhat larger. Force measurements were also carried out on this double model carried out, which led to equally good results.

Three-component measurements were also made with the same shape carried out on a normal model (not a double model) with soil simulation in the wind tunnel. 7a, 7b, 7c show this Model now in a similar arrangement again a side view (Fig. 7a), a front view (Fig. 7b) and a top view (Fig. 7c), but here as a single model, the vehicle wheels 14 still being indicated for the sake of clarity. To the Model according to Fig. 7a, 7b ,. 7c is a drawn-in dent 15 in the area of the base plate at the transition point between the front part 10 and the area of the windshield 11 of particular Meaning. This is intended to result in an excessive flow over the lower longitudinal edge of the vehicle in the area of the increase in width

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be avoided. These measurements also showed the good ones aerodynamic properties of this form.

8a, 8b, 8c illustrate a body shape in which in Transition area between the front part 10 and the windshield 11, a constriction 16 is provided in the vehicle width is. This constriction is arranged to taper in the direction of the floor panel and is therefore essentially in effective upper area, that is to say on the upper longitudinal edge of the front part 10 or the front pane 11. The different from each other assigned lines illustrate this.

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List of reference symbols

1 = Body cross-section 2 = Street 3 = Long edge 4th = Side wall 5 = Vortex 6th = Mirror image 7th = Side view 8th = Front view 9 = Top view 10 = Front part 11th = Windshield 12th = Rear 13th = Passenger cell 14th = Vehicle wheels 15th = Dent 16 = Constriction

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Claims (1)

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YOUR REF. German research and experimental institute for. Air and Raumfahrt e.V., Linder Höhe, 5000 Cologne 90 Fluid body for vehicles Patent claims: (1. E aerodynamic body for vehicles, in particular ^ - £ -ür passenger cars, with an approximately rectangular cross-section having the passenger compartment, which has at least one inclined. Front window, characterized in that before and / or after the A change in height of the body cross-sections (1) in the longitudinal direction is associated with a change in width such that only a small flow around the edge (transverse flow around the upper longitudinal edge of the vehicle) without separation of the flow or without any significant separation. 2-. Body according to Claim 1, characterized in that in the case of a passenger cell (13) with a height-to-width ratio of about 1: 1.2 to 1.3, a lateral widening of the body in the area of the windshield of 50 to 150% of the height change is provided in the area of the windshield. -.---. . COPY _ ο - 3. Body according to claim 1 or 2, characterized in that that it is rapidly increasing in width in the area of the inclined windshield (11) and in the area of the passenger compartment (13) has essentially constant height and width, and that the rear section adjoining the passenger compartment (13) (12) has decreasing height and decreasing width in the direction of the body end. 4. Body according to claim 3, characterized in that the decrease in height and width at the rear section (12) gradually, is preferably provided with angles of about 15 ° to 20 °. 5. Body according to one of claims 1 to 4, characterized in that that to realize a large track width in the area of the front wheels, the body in the transition area between the front part (10) and the front window (11) has a constriction (16) in the width. 6. Body according to claim 5, characterized in that the constriction (16) is provided essentially in the upper area and tapering in the direction of the floor panel is arranged. 7. Body according to one of claims 1 to 5, characterized in that that they have a on the floor panel in the transition area between the front part (10) and the front window (11) has a drawn-in dent (15) whose strongest constriction is arranged approximately at the beginning of the front window (11). 8. Body according to one of claims 1 to 7, characterized in that that the corners of the body cross-sections (1) in the area of strong cross-sectional changes to allow flow around corners without significant flow separation are rounded.