GB2372018A

GB2372018A - Controlling airflow around a vehicle

Info

Publication number: GB2372018A
Application number: GB0202974A
Authority: GB
Inventors: Andrew Shaw
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-02-08
Filing date: 2002-02-08
Publication date: 2002-08-14
Anticipated expiration: 2022-02-08
Also published as: GB0103091D0; GB0202974D0; GB2372018B

Abstract

Multiple vortex generating means, such as serrated strips (30 figure 3) are mounted on or form part of a vehicle at flow disturbance generating zones, especially trailing edges to create micro turbulence which is intended to improve airflow around the vehicle. The strip may comprise cusped projections (31) having various shapes which may be similar to birds feathers for example. The projections may have a second level of serrations along their edges (figure 4).

Description

Controlling Airflow Around Surface Vehicles

This invention relates to a means for controlling airflow around surface vehicles, particularly those such as motor road vehicles which attain low surface subsonic speeds, for example in the range up to 120 kmph (about 75 miles per hour).

Aerodynamic drag is caused by the turbulence in the air caused by movement of a vehicle through the air. The vehicle pushes air aside, and the air comes back together in the wake of the vehicle. Both the initial displacement, and the reentry into the wake create turbulence, which derives its energy from the motion of the vehicle, thus creating drag and reducing the efficiency of motion of the vehicle. Streamlining or aerodynamic profiling offers a partial solution, as this is usually applied to the front of the vehicle thus reducing leading edge turbulence. For practical and economic reasons, the rear of the vehicle is usually not profiled, but more or less abruptly"cut-off"leaving considerable wake turbulence, which is clearly evidenced by the manner in which spray from a wet road is blown about in the wake of even a small vehicle. For practical design reasons ideal streamlining is not usually approached with everyday vehicles, and vehicle bodies have several air disturbance generating zones, such as front and rear edges, created by their body shell shape. In aircraft it is known to for example provide winglets at the tips of the aircrafts wings to reduce vortex disturbance and wake magnitude here the above and below wing

flow regimes contact at the wing tip. Solutions developed for use at high subsonic speeds, such as in aircraft, are not always fully applicable for use at low subsonic speeds however.

It is an object of the invention to provide a practical low cost means for improving airflow patterns to for example reduce drag and disturbance in low velocity vehicles such as ordinary motor road vehicles, given that ideal solutions, based on aerodynamic theories are not feasible for practical and economic reasons.

According to the invention, from a first aspect, there is provided means for reducing drag and wake disturbance disposed on a vehicle body with a multiple vortex generating means. From another aspect there is provided a vehicle provided with such multiple vortex generating means located thereon. The vortex generating means may for example be located on at least one air flow disturbance generating zone, in an imperfectly stream lined vehicle.

The term Jlair flow disturbance generating zone"on a vehicle means any zone in a vehicle body where laminar flow breaks down to turbulent or other disturbed flow notably, but not exclusively at leading or trailing edges.

The disturbance generating zone may be provided with an attached strip carrying the multiple vortex generating means to for example a leading trailing or side edge built provided at the rear of the vehicle during construction of the vehicle. Zones such as leading trailing or side edges

which may be thus equipped include horizontal edges such as the front or rear edge of the roof of the vehicle, and or of the boot of a saloon car, and also upright edges, whether sloping or vertical, at the sides of the vehicle.

Lines of vortex generators may be provided on the body disposed in a generally fore and aft alignment, parallel to the direction of motion, and placed to interfere with lateral air movement between high and low pressure zones. Where the vehicle cross-sections is a fore and aft aerofoil but with straight side panels, the lines may be provided along the edge of the curved top abutting the side panels. In the case where the lateral cross section is also curved, the optimum position may have to be determined by experiment.

The configuration of vortex generating means provided at each separation zone, leading or trailing edge or elsewhere so equipped may be determined by experiment, but a shape which is favoured is derived from the shape of the rear edge of the primary feathers of a birds wing, producing a scalloped edge or other repetitive shape. One shape which seems to produce useful results for use in an upright edge, comprises, for each serration a horizontal (relative to the ground on which the vehicle is running or standing) upper edge, with an undercut lower edge, leaving a reentrant part or bight on the lower edge of the serration. Where the zone, e. g. an edge to which the serrations are applied either as a strip fixed to the vehicle body adjacent the edge, or as part of the vehicle structure, is

inclined (as in the case of a rear window, or hatch back door), the effect may be to provide an overall shape similar to a series of undercut steps.

The size of the serrations may vary from a spacing (point or cusp to point or cusp) and depth in the order of 100 to 150mm, to 15 to 25mm, or smaller.

In the case of serrations applied to an edge, such as the rear edge of a roof and/or the boot of a car, these may be in the form of convex or concave bays, e. g. following the patterns of avian tail feathers, producing an arched profile having pointed cuspid projections between them. The projections may be reinforced with upward or downward oriented ribs to act as flow baffles and mechanical reinforcements.

The serrations may be provided on strips of polymer or rubber, or metal for attachment to the vehicle body at appropriate locations.

Attachment may be by any suitable means such as nut and bolt, adhesive, friction etc. as appropriate for the materials used The invention is based on the premise that large scale air disturbance such as turbulence produced in the wake of a vehicle can be broken up and the resistance or drag generated by this turbulence or disturbance of laminar flow reduced, by deliberate creation of smaller scale vortices which by their nature should have a smaller total energy. By appropriate scale choice, the vortices interact to reduce turbulence and disturbance to laminar flow rather than to create such effects.

A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, wherein : Fig. 1 shows diagrammatically airflow patterns, simplified, arising due to motion of a vehicle not modified in accordance with the invention.

Fig. 2 is a fragmentary view of a vehicle modified by mounting a device according to the invention on one trailing edge; Fig. 3 is a perspective view of a strip for mounting on edge such as a leading trailing or side edge of a car body in accordance with the invention; and Fig. 4 is a view similar to figure 3 of a second form of strip.

In Fig 1 the known vehicle 10, displaces air along arrows 11 as it moves. This is shown as substantially laminar, over the front part of the vehicle whereas in practise, there would be vortices and turbulence created at surface discontinuities providing air flow disturbance generating zones such as the front of the bonnet, and the top of the windscreen. The main air flows about the vehicle produce wake turbulence shown by major vortices, a top vortex 12, and a bottom vortex 13, as well as side vortices (not shown) as over pressure air compressed by displacement by the vehicle, tries to enter the under pressure zone immediately following the moving vehicle. The turbulence creates induced"drag", and reduces the efficiency of the motion.

In accordance with the invention, at least one and preferably all trailing edges or other airflow disturbance generating zones (as above defined) marking surface discontinuous are fitted with serrated members.

Fig 2 shows a serrated member 20, fitted to the side of the rear window of a car. The serrations are characterised by a horizontal top edge 21, leading to a cusp 22, and a re-entrant lower edge 23, producing an overall stepped profile. The serrations produce a plurality of controlled minivortices rather than a single large vortex. A further member 25 is attached to the rear edge of boot 26. In addition serrated members 29 are provided along the side edges of the car roof and boot. The serrations 27 of this are arched shaped projections with points 28 from which vortices are generated. The scale of the serrations shown is for illustrative purposes only, and the serrations may be much smaller e. g. about 25mm cusp or point to cusp or point, and about 15mm deep. Fig 3 is a perspective view of a strip 30 for attachment to a horizontal edge, such as the rear edge of a car roof or a boot. The strip 30 is characterised by projections 31, with cuspid points 32, at apexes of the arch shaped projections 31 from which vortices are induced. Optional upper fins or fences may be provided.

The spacing of the points 32 may be about 25mm with indents between them in the order of 15mm deep. The serrations may however be much larger (or smaller).

Here again, the eddies formed at the horizontal trailing edge are

broken up by steady mini-vortices induced by the points 32, assisted by the fences 33 and/or 34 if present. The edges of projections 31 may be ground to a knife edge.

Preferably, all the rear edges top and side edges, and other disturbance generating zones of the major surfaces of a vehicle body are equipped with such serrated strips and or fins. These may be formed by as part of the vehicle bodywork, or provided as separate strips for retro fitting to existing vehicles and maybe flexible or rigid. Other locations include the side edges and trailing edges of mudguards and flaps for example.

The shape of the strips may preferably be based upon the configuration of the rear edge of the primary feathers of a bird's wing, producing a scalloped edge as shown in Figure 3. The indentations may themselves be formed with second order indentations as in figure 4, so that each projection itself has a serrated edge. Four different sub-indentation profiles are shown by way of example.

The means described can be fitted to all manner of land vehicles, including trucks, cars and coaches. As well as reducing aerodynamic drag the device of the invention should beneficially reduce spray fog or dust arising when driving after rain.

Examples of locations include the leading edges of non-streamlined vehicles, such as the horizontal vertical and inclined edges of a truck or van cab and body, including any wind deflector shield if present. Without the devices of the invention, the leading edges create a bow wave, which produces a vacuum alongside the vehicle body, and at trailing edges a wake void into which displaced air is drawn with turbulence. Both produce suction acting on the vehicle and producing retardation, which requires additional tractive effort to overcome so reducing efficiency. With the means of the invention micro-turbulence is created rather than large scale bow and wake fronts which allows a better approximation to laminar flow to be maintained along the vehicle body and in its wake.

Claims

Claims 1. Means for controlling air flow around a vehicle comprising means for generating multiple vortices adapted to be mounted or formed on a vehicle body.
2. Means according to claim 1 wherein said means for generating multiple vortices comprises a member having an edge shaped to define a plurality of cusps or points.
3. Means according to claim 2 wherein said shaped edge comprises a serrated edge comprising outwardly extending points separated by inwardly extending indents, connected by convex curved or straight edges.
4. Means according to claim 3 wherein said serrated edge is formed as a knife edge.
5. Means according to claim 2 wherein said member provides outwardly directed points each defined by one straight edge and one concave curved edge.
6. Means according to anyone of claims 2 to 5 wherein said member comprises a strip having said serrated edge with means for mounting said strip on a vehicle body.
7. Means according to claim 6 in which some at least of said points have ribs or fences thereon.
8. Means according to claim 6 wherein said serrated edges are

themselves formed with second order serrations.
9. A vehicle comprising a body on which is mounted or formed one or more means for generating multiple vortices according to anyone of claims 1 to 8.
10. A vehicle according to claim 9, wherein each said means for generating multiple vortices is located at a flow disturbance generating zone.
11. A vehicle according to claim 10 wherein said means for generating multiple vortices is located at a leading trailing or side edge, to induce micro-turbulence to as to prevent creation of larger scale drag-creating turbulence.