GB2502514A

GB2502514A - A drag reduction method and material

Info

Publication number: GB2502514A
Application number: GB1208081.8A
Authority: GB
Inventors: Dimitris Katsanis; Robert William Lewis
Original assignee: UK Sport Ltd
Current assignee: UK Sport Ltd
Priority date: 2012-05-09
Filing date: 2012-05-09
Publication date: 2013-12-04
Also published as: GB201208081D0

Abstract

A method of reducing drag on a body 1 in an air stream 7 and a material 2 is provided. The method comprises the covering of the body 1 with a material 2 comprising , for example, a fleece spacer layer 3 covered in a woven layer of nylon which has a windproof coating 5 thereon. The material is breathable, allowing the formation of one or more elongate bubbles 8 beneath the surface of the windproof coating 5, the elongate bubbles 8 being aligned normally to the direction 6 of the air flow 7. A material for covering a body 1 comprising a spacer layer 3, a woven layer and a windproof coating 5 applied to the woven layer is also disclosed.

Description

Drag Reduction Method and Material This invention relates to a new drag reduction method and materials therefor. The method and materials are applicable to sports clothing where drag on body elements can be a significant factor in performance, or br providing a surface layer on a blunt body to reduce the wind drag on the body. Examples of applications of the material include cyclists' clothing and coverings for yacht masts to reduce wind drag.

According to the present invention a method of reducing drag on a body in and air stream comprises the step of covering the object with a material having a windproof coating thereon and forming one or more elongate bubbles beneath the surface of the windproof coating said elongate bubbles being aligned normally to the direction of the air flow.

In one embodiment the alignment of elongate bubbles subtends an angle of 713° to 95° to the direction of the air flow.

Preferably the material comprises a wind poof coating on a woven material itself over a spacer material.

The spacer material is normally between 2 and 4mm inclusive thick. The nature spacer material is not critical, although a fleece material would usually be deployed.

The woven material is conveniently nylon and the windproof coating conveniently polyurethane.

In this specification the word body means both a human body, a mammal or animal body, or an inanimate object.

In another embodiment the invention, a material to cover a body or an object or part of such a body or object comprises a wind poof coating on a woven material itself over a spacer material.

In one arrangement said a windproof layer has a plurality of rows of holes through which wind may enter and leave between the windproof layer and the body.

It has been found that in a method according to the invention, the material, will form a bubble on the surface of the body at an angle of about 7Q° to 95°to the wind direction causing the flow of wind around the body to break away from the surface of the body producing a streamline-like effect and reducing thedrag c*i the body.

Without the streamline effect the laminar flow of wind around the body would to continue around the body from an upstream surface to a downstream surface eventually to break away from the surface in a turbulent flow which is the source of significant drag.

When the windproof layer has holes, it has been found that holes of between about 1mm and 2 mm work effectively. Normally the holes are distributed in parallel rows in the material so that when the material is formed into an item of clothing or as a drag reduction layer for a blunt body the parallel rows are parallel to axis of a limb or other body part of the person, or, when used to reduce the drag of a blunt body, to the axis of the blunt body. It has been found that smaller sized holes shows the greatest reduction in the drag coefficient but the reduction occurs at a higher wind velocities than for a larger holes. Clearly there is the possibility ot tuning the material to the particular application envisaged Any combination of compatible windproof layer coating on a woven layer can be used. For clothing for cycle racing, a fleece covered with a more breathable material such as Lycra® coated with a windproof and waterproof layer, such as BemisTM, works well. The holes are made by laser, about 1.5mm in diameter arranged in rows; the holes on the rows are about 5mm apart. The rows themselves are about 5mm apart.

To explain the invention more fully, reference is made, by way of example only, to the accompanying drawings in which; Figure 1 shows a section showing the invention in operation; Figure 2 shows in side section a material having laser cut holes according to the invention; Figure 3 shows a top section of a material shown in figure 2; Figure 4 shows test rults obtained using a test piece comprising a rod of dodecagon cross section, covered with a material according to the invention and subject to a head on wind of increasing velocity In figure 1 a body, which in this case is a thick rod 1, illustrative of an arm or a yacht mast, is shown in cross section. The rod 1 is covered with a triple layer material 2, comprising a fleece spacer layer 3, covered with a woven layer nylon, which has been coated with polyurethane 5. The rod 1 with the material covering 2 is placed in an air flow 7 coming from a direction 6 towards the rod 1. As the speed of the air flow increases a pair of elongate bubbles 8 form in material 2. The alignment of the bubbles is normal to the air flow. The bubbles 8 cause the flow around the rod to become detached and stream away being the rod. This detached flow leads to a significant reduction in drag caused by the rod (as illustrated in figure 4 below). The angle 9 subtended by a line through the centre of the bubbles 8 to the centre of the rod to a line 10 through the centre of the rod normal to the direction 6 from which the air flow comes is initially between 20° and 10°,i(e. 70° to 80° to the direction 6 from which the air flow comes). As the speed of the air flow increases, the angle 9 decreases eventually to about -5° to the normal 10 4.e. about 95° to the direction from which the air flow is coming), at this point no further change occurs.

In figures 2 and 3, a material 11 to be used in the manufacture of the arms of a cyclist's racing suit is showrt It comprises a first layer of a breathable nylon material 13 (such as Lycra ®) coated with a windproof layer 15 which is also water and oil repellent. The nylon layer covers a fleece layer 14, 2mm to 4mm thick, next to the cyclist's skin. The layer 15 has been laser treated to form rows of small holes, each hole being about 1.5mm in diameter and separate from the adjacent holes in its row by about 5mm. The rows themselves are arranged around the arm or thigh of a cyclist, and separated by about 5 mm. In practice it is easier to manufacture the material with holes around the body parts of interest, even though only those holes up-wind of the body part will be effective. As a cyclist wearing the suit having the material of the invention in his its arms, thighs and/or legs, wind will pass the cyclist from the head on direction and will enter into the suitthrough holes in the forward rows of holes under the wind proof layer 15 and travel around the arm of the cyclist before leaving though rows at about +/-75° to thedirection of travel. This causes the material to lift very slightly from the arm of the cyclist, effectively forming a deflector in a line parallel to the axis of the arm of the cyclist so diverting the air flow away from the rear of his/her arm, and reducing drag thereon.

Figure 3 shows the results of trails using a rod of roughly arm like proportions with a regular dodecagon cross section subject to a head on wind. The rod was covered with materials in accordance with the invention. The principle difference between the trials was the hole sizes used and the angle of the first row of holes with respect to the head-wind. In practice it was found that the angle subtended by the first row of holes into the head wind was not particularly critical. In figure 3 curve 20 shows the test results using a rod coveied with a plain PlastotexTM material without laser holes.

The drag is normalised at 1 for this material at an equivalent wind speed of 1 Om/s (Reynolds Number 70000). As the wind speed increases, following line 20, it can be seen that the drag does not vary much. Looking at lines 22 and 24, which show the results forthe same PlastotexTM material having rows of laser cut holes, the rows being parallel to the axis of the test rod, in accordance with the invention, the drag reduces very sharply above 20 m/s and remains low and constant as speed increases. The difference between curves 22 and 24 is that in the case ot curve 22 the first row of holes was at an angle of 30° to the head wind and in the case of curve 24 it was at 45°. It will be seem that the results show that thealignment of the first row of holes relative to the head wind is not especially sensitive. In both cases the holes themselves were 1.5mm in diameter.

More interesting is the effect of varying the holes. Curve 26 is for a material ha4ng smaller holes (1.25mm) aligned in the same way as curve 22. The impact is large, with the significant drop in drag occurring at a lower Reynolds number (about 1.2*1 0), but the drop is not quite as great as for the larger holes used to produce the curves of 22 and 24. Further rejuctions in hole size down about 1mm moved the position of the drop to the left, just above a Reynolds Number of 0.7*105 but with the lowest drag being higher at 0.7, bigger holes moved the drag reduction to the right, however, the improvement in drag performance was no better than that shown for curves 22 and 24 in figure 3.

The results obtained and in particular the marked reduction of drag are very significant and when applied to a cycling suit result in significant drag reductions at typical speeds reached in racing cycling.

Although the invention has been described in relation to a cycling suit, the principles can be applied to any number of situations. For example a material according to the invention applied to the mast of a yacht would result in reduction of the drag created by the mast.

Claims

Claims 1. A method of reducing drag on a body in and air stream comprkng the step of covering the object with a material having a ndproof coating thereon and forming one or more elongate bubbles beneath the surface of the windproof coating said elongate bubbles being aligned normally to the direction of the air flow.
2. A method according to claim 1 wherein the alignment of elongate bubbles subtends an angle of 70° to 95° to the direction of the air flow.
3. A method according to claim 1 or 2 in which the material comprises a windproof coating on a woven material itself over a spacer material
4. A method according to claimS in which tie spacer material is between 2 and 4mm inclusive thick.
5. A method according to claimS or 4 in which the spacer material is a fleece.
6. The method according to any preceding claim in which the windproof coating is polyurethane.
7. A method according to any preceding claim in which the material comprises a windproof layer having a plurality of rows of holes through which wind may enter and leave between the windproof layer and the body.
8. A method according to claim 7 diaracterised in that the holes between about 1mm and 2mm in diameter.
9. A method according to claim 8 diaracterised in that the holes are about 1.5 in diameter.
1 0.A method according to claim 7, 8 or 9 characterised in that the holes are in rows, said rows being parallel to an axis of a body on which the material is mounted.
11.A method according to any one of claims 7 to 10 Wierein the holes are about 5mm apart.
1 2.A method according to any one of claims 7 to 11 in which the holes are laser cut holes.
1 3.A material to cover a body or an object or part of such a body or object comprising a spacer layer, a woven layer and a windproof coating applied to the woven layer.
14.A material according to claim 13 in which the spacer material is between 2 and 4mm inclusive.
15.A material according to claim 13 or 14 in which the spacer material is a fleece.
1 6.A material according to claim 13, 14 or 15 in which the wind proof coating is polyurethane.
17. A material according to any one of claims 13 to 16 wherein the windproof layer has a plurality of rows of holes through which wind may enter and leave between the windproof layer and the body.
1 8.A material according to claim 17 characterised in that the holes between about 1mm and 2mm in diameter.
1 9.A material according to claim 18 in which the holes are about 1.5mm in diameter.
20.A material according to anyone of claims 17 to 19 charaderised in that the holes are in rows said rows being parallel to an axis of a body on which the material is mounted.
21.A material according to any one of claims 17 to2O wherein the holes are about 5mm apart.
22.A material according to any one of claims 17 to2l in which the holes are laser cut holes.
23.A material according to any one of claims 13 to 22 placed around a body or part thereof and forming a one or more bubbles between the body and the material in an air flow.
24.A material according to anyone of claims l3to 23 comprising part of a cyclist's suit.
25.A method of reducing drag on a body in an air flow substantially as hereinbefore described with reference to the accompanying drawings.
26.A material substantially as hereinbefore described with reference to the accompanying drawings.