Land vehicles: bodies and tops – Bodies – With distinct wind deflector
Patent
1993-02-05
1995-04-18
Pedder, Dennis H.
Land vehicles: bodies and tops
Bodies
With distinct wind deflector
296185, 296208, B62D 3500
Patent
active
054072450
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for reducing the drag in the rear region of a vehicle, for example, a road or rail vehicle or the like.
In addition, the invention relates to a device for carrying out this process.
The development of energy-saving and ecologically harmless vehicles, particularly motor vehicles for road traffic or railbound vehicles, mainly requires a reduction of their drag. As tests have shown in the field of motor vehicle dynamics, large-area flow separations may occur on different regions of the vehicle shell inducing intensive swirling movements. Such physical occurrences are connected with high energy dissipations which, in turn, represent the causes of high air resistances but also of undesirable lift forces with respect to a vehicle.
The important region where the undesirable flow conditions are particularly obvious is the whole rear region of a vehicle. It is known that the largest proportion of the drag of, for example, a motor vehicle, is the pressure resistance which, for example, in the case of a modern passenger car, may amount to more than six times the proportion of the frictional resistance. This drag is decisively determined by the separated, intensively swirled flow region, the so-called eddying zone, in the rear region of the vehicle.
From the German Patent Document No. 649 343, a flow retarder for high-speed motor vehicles is known which provides that air blown out toward the longitudinal direction of the vehicle is extracted in the rear region of a vehicle. As a result of this measure, the author of this patent document wants to achieve a deceleration of the vehicle.
An opinion was expressed with respect to the above-mentioned patent document in the journal Motorkritik, Year 1941, Pages 223, and on, under the heading "Air Resistance Helps Deceleration". The opinion states in detail on Page 256 that the view expressed at the time by the author of the patent document was incorrect and explains in detail that of the air extraction, a form of boundary layer suction takes place and as a result a longer adhering of the flow or a reduction of the swirl drag is achieved.
The invention is based on the object of further developing a process, in which air is blown out and sucked in again in the rear region of a vehicle, in such a manner that a reduction of the total resistance of the vehicle is achieved. In addition, the invention is based on the object of providing a device by means of which the process according to the invention can be carried out efficiently.
Because of the interaction between the process measures a, b and c according to the invention, that is, because of the interaction of tangential boundary layer blowing-out, of the Coanda effect and of boundary layer suction, an at least partial suppression of the eddying zone is obtained in the rear region and thus a considerable reduction of the drag of the vehicle.
It is known that the "Coanda effect" is the characteristic of fluid jets (liquid or gas jets) to place themselves on fixed walls situated in the proximity and flow along them, the fluid jet being deflected from its original propagating direction.
As a result of the process according to the invention, first a targeted blowing-out of air therefore takes place in the area of the separating line(s) of the vehicle rear, specifically at a relatively high speed. Secondly, the Coanda effect is utilized which provides in particular that the flow places itself against a curved surface, the flow taking place against or around it. Thirdly, the air is finally sucked again from the eddying zone. This combination of measures causes the achieving of the overall effect; i.e., Bernoulli's total pressure in the rear region is increased, and as a result the pressure resistance and therefore the overall drag is reduced or minimized sufficiently.
The speed of the blown-out air jets is set sufficiently high, particularly to approximately 50 m/sec.; i.e., higher than the ambient speed so that the Coanda effect can be properly utilized. For this purpose, it is provided in certain e
REFERENCES:
patent: 2037942 (1936-04-01), Stalker
patent: 2242494 (1941-05-01), Wolf
patent: 3591229 (1971-07-01), Wilfert et al.
patent: 4393852 (1983-07-01), Merritt et al.
patent: 4460055 (1984-07-01), Steiner
patent: 5184832 (1993-02-01), Miwa
Daimler-Benz AG
Pedder Dennis H.
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