LOW DRAG GARMENT

Abstract

A low drag garment comprises a textured fabric in at least one side region of the garment, wherein the textured fabric has a substantially uniform texture height in the range 0.2-0.8 mm.

Claims

1. A low drag garment comprising a textured fabric in at least one side region of the garment, wherein the textured fabric has a texture pattern with a substantially uniform texture height in the range 0.2-0.8 mm.

2. A low drag garment according to claim 1, wherein the textured fabric has a texture pattern with a substantially uniform texture height in the range 0.3-0.7 mm, preferably 0.4-0.6 mm.

3. A low drag garment according to claim 1, wherein the garment includes a body portion and the textured fabric is provided in at least one side region of the body portion, and wherein the textured fabric in the side region of the body portion has a texture pattern with a substantially uniform texture height in the range 0.2-0.4 mm.

4. A low drag garment according to claim 3, wherein the garment includes a sleeve portion and the textured fabric is provided in at least one side region of the sleeve portion, and wherein the textured fabric in the side region of the sleeve portion has a texture pattern with a substantially uniform texture height in the range 0.3-0.8 mm.

5. A low drag garment according to claim 3, wherein the garment includes a leg portion and the textured fabric is provided in at least one side region of the leg portion, and wherein the textured fabric in the side region of the leg portion has a texture pattern with a substantially uniform texture height in the range 0.2-0.4 mm.

6. A low drag garment according to claim 1, comprising a relatively smooth fabric in at least one front region of the garment, wherein the relatively smooth fabric has a texture height of less than 0.2 mm.

7. A low drag garment according to claim 1, comprising a textured fabric in at least one rear region of the garment, wherein the textured fabric in the rear region of the garment has a texture height of at least 0.4 mm.

8. A low drag garment according to claim 1, wherein the side region of the garment comprises a region of the garment in which the surface angle has a minimum value .sub.1 in the range 5 to 45, and a maximum value .sub.2 in the range 95-160.

9. A low drag garment according to claim 1, wherein the side region of the garment comprises a region of the garment having a width in the range 30-170 mm.

10. A low drag garment according to claim 1, wherein the textured region has a texture pattern that comprises a plurality of isolated texture formations separated by regions with substantially no surface texture.

11. A low drag garment according to claim 10, wherein the texture formations are arranged in rows that extend transverse to the direction of airflow, wherein the rows have a mean spacing D in a direction of airflow in the range 1 mm to 10 mm.

12. A low drag garment according to claim 11, wherein the texture formations forming the rows have a mean spacing G in a direction perpendicular to a direction of airflow in the range 1 mm to 10 mm.

13. A low drag garment according to claim 1, wherein the fabric has a texture pattern that is provided by jacquard knitting of the fabric, or by printing a 3D pattern on the outer surface of the fabric, or by the application of a solid material to the outer surface of the fabric.

14. A low drag garment according to claim 1, wherein the garment is an article of sports clothing.

15. A low drag garment according to claim 14, wherein the garment is an article of sports clothing for use in cycling, running, skiing, horse racing or speed skating.

16. A low drag garment according to claim 14, wherein the garment is an article of sports clothing for use in a sport where an athlete typically travels at a speed in the range 5-20 m/s.

17. A low drag garment according to claim 1, wherein the garment is a shirt, trousers, leggings, shorts, bibshorts, shoes, overshoes, arm covers, calf guards, gloves, socks or a bodysuit.

18. A low drag garment according to claim 2, wherein the garment includes a body portion and the textured fabric is provided in at least one side region of the body portion, and wherein the textured fabric in the side region of the body portion has a texture pattern with a substantially uniform texture height in the range 0.2-0.4 mm.

19. A low drag garment according to claim 4, wherein the garment includes a leg portion and the textured fabric is provided in at least one side region of the leg portion, and wherein the textured fabric in the side region of the leg portion has a texture pattern with a substantially uniform texture height in the range 0.2-0.4 mm.

20. A low drag garment according to claim 5, comprising a relatively smooth fabric in at least one front region of the garment, wherein the relatively smooth fabric has a texture height of less than 0.2 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:

[0038] FIG. 1 illustrates schematically the flow of air around a cylindrical object;

[0039] FIG. 2a illustrates graphically the results of a set of tests investigating the variation of drag coefficient (Cd) with air speed for various textured fabrics on an 80 mm radius cylindrical body;

[0040] FIG. 2b illustrates graphically the results of a set of tests investigating the variation of drag coefficient (Cd) with air speed for various textured fabrics on a 130 mm radius cylindrical body;

[0041] FIG. 3 is a plan view of an exemplary texture pattern according to an embodiment of the invention;

[0042] FIG. 4 is a sectional view of the exemplary texture pattern on line A-A of FIG. 3;

[0043] FIG. 5 is a sectional view of the exemplary texture pattern on line B-B of FIG. 3;

[0044] FIG. 6 is a front view of a cyclist wearing a bodysuit for cycling; and

[0045] FIG. 7 is a side view of the cyclist wearing the bodysuit shown in FIG. 6.

DETAILED DESCRIPTION

[0046] For the majority of the applications in which use of the invention is envisaged, the Reynolds number will have a value of up to 10.sup.6, such that the flow of air will be in the laminar/turbulent transition zone. We have used wind tunnel testing to understand and derive optimum textures for use in the invention, and in particular on garments that are worn in applications where they are exposed to an airflow with a speed in the range 5-20 m/s, preferably 10-20 m/s.

[0047] In order to simplify experimentation, much of our research is based on optimising the drag around cylindrical objects with radii of 80 mm and 130 mm. This has enabled us to identify the surface requirements for a wide range of applications. Testing is conducted at a range of speeds and consideration is also given to wind direction. Within the sizes of cylinder used it is possible to approximate a range of curvatures that the airflow will encounter on a human body in a range of applications. For example, for an adult, the upper arm typically has an average radius (based on circumference) of about 50 mm, the thigh typically has an average radius of about 80 mm, and the chest typically has an average radius of about 160 mm. It is of course recognised that the human body is not a perfect cylinder and in regions such as the chest it is closer to an elliptical shape. However, a cylinder provides a good first approximation to an irregular curved body in which the radius of curvature is similar to that of the cylinder.

[0048] FIG. 1 illustrates a typical airflow around a cylindrical body 2, wherein the longitudinal axis X of the cylindrical body is perpendicular to the direction of airflow relative to the cylindrical body. It will be understood that the movement of a body through stationary air may be modelled in a wind tunnel by creating a moving airstream that flows over a stationary body, as depicted in the drawings. In this example the direction of airflow as indicated by arrow S is perpendicular to the surface of the cylindrical body at point P, which is called the stagnation point. This is equivalent to forward relative movement of the body 2 through the air in the direction of arrow M.

[0049] On either side of the stagnation point P the airflow splits into two streams F.sub.1, F2 that pass around opposite sides of the cylindrical body 2. Up to approximately the widest point of the cylindrical body relative to the flow direction, the airflow is substantially laminar, allowing a boundary layer to build up against the surface of the cylindrical body 2.

[0050] After passing the widest point of the cylindrical body 2 relative to the direction of flow, the flow streams F.sub.1, F2 tend to separate from the surface of the cylindrical body forming vortices V in the region behind the cylindrical body. This creates a low pressure zone L behind the cylindrical body 2 and the resulting pressure difference between the front and the rear faces 5, 6 of the cylindrical body creates a pressure drag force F.sub.d that opposes movement of the cylindrical body relative to the air. The movement of air over the surface of the cylindrical body also creates a surface friction force F.sub.s, which is usually much smaller than the drag force F.sub.d at relative speeds in the range 6-40 m/sec.

[0051] The points where the boundary layer separates from the surface of the cylindrical body 2 are called the transition points T.sub.1, T.sub.2. The pressure drag force F.sub.a experienced by the cylindrical body 2 depends in part on the area of the cylindrical body located within the low pressure zone L between the transition points T.sub.1, T.sub.2. If the transition points T.sub.1, T.sub.2 can be moved rearwards, this will reduce the size of the area affected by the low pressure zone L, thereby reducing the pressure drag F.sub.a acting on the cylindrical body 2.

[0052] It is known that the transition points T.sub.1, T.sub.2 can be shifted rearwards by providing a suitable texture 8 on the surface of the cylindrical body 2. It should be understood that the texture pattern 8 shown on the upper part of the cylindrical body 2 may also be repeated on the lower side of the body. In the present invention we have sought to design a fabric with a substantially uniform surface texture, which maximises the reduction in pressure drag F.sub.d without significantly increasing surface friction drag F.sub.s.

[0053] As illustrated in FIG. 1 we have discovered that the pressure drag force F.sub.a can be reduced substantially, without significantly increasing the surface friction drag force F.sub.S by covering the cylindrical body 2 with a fabric 3 having a texture pattern 8 comprising a plurality of texture formations 8a on at least the side regions of its outer surface, between the front face 5 and the rear face 6 of the cylindrical body 2. The size of the side region can be expressed in terms of the surface angle , which is the angle subtended between the direction of forward movement M and a line 7 that is perpendicular to the surface of the cylindrical body.

[0054] Our research has identified the optimum height and spacing of the surface texture formations for a range of curvatures, speeds, and onset flow angles. This has allowed us to derive a simple texture pattern that can be utilised to give an optimum level of airflow perturbation without being sensitive to flow direction changes, whilst minimising the surface friction drag through effective spacing of the texture formations 8a that form the three-dimensional texture pattern 8.

[0055] Much research has been done into the change in the drag on a cylindrical body through a range of speeds. It is well known that the drag coefficient falls and then increases again as the speed of the airflow increases for a given cylinder size. This is due to vortex formation and periodic shedding, which affects the laminar transition points behind the cylindrical body.

[0056] Our research has enabled us to modify this flow behaviour through the use of variable surface textures and thus minimise the pressure drag for the speed range in question (5-20 m/s). We have conducted a series of wind tunnel tests to determine how different textured fabrics affect the drag coefficient for 80 mm and 130 mm radius cylinders at air speeds ranging from 3 m/s to 25 m/s. The results are illustrated in FIGS. 2a and 2b.

[0057] In FIG. 2a the wind tunnel test results are illustrated for a plain 80 mm radius cylinder and for six different fabrics on an 80 mm radius cylinder, the fabrics being as follows: [0058] Sample Aa prior art textured fabric that performs best at high speeds; [0059] Sample Ba prior art textured fabric that performs best at low speeds; [0060] Sample Ca new fabric comprising an embodiment of the invention, having a silicone chevron texture pattern with a spacing of 7 mm and a constant texture height of 0.4 mm; [0061] Sample Da new fabric comprising an embodiment of the invention, having a silicone chevron texture pattern with a spacing of 7 mm and a constant texture height of 0.5 mm; [0062] Sample Ea new fabric comprising an embodiment of the invention, having a silicone chevron texture pattern with a spacing of 7 mm and a constant texture height of 0.6 mm; [0063] Sample Fa new fabric of the type described in EP16165668.1, which does not comprise an embodiment of the invention, having a silicone chevron texture pattern with a spacing of 7 mm and a texture height that increases gradually from 0.5 mm to 5.0 mm (the portion with the smallest texture height being positioned on the front part of the cylinder).

[0064] The fabrics were all wrapped around the circumference of the cylinder for the test.

[0065] As can be seen in FIG. 2a, the prior art Sample A fabric performed well at speeds above 17 m/s, having a drag coefficient Cd of less than 0.72 at air speeds between 17 m/s and 23 m/s, but less well at lower speeds, the drag coefficient rising rapidly at air speeds of less than 17 m/s to a value in excess of 1.00 at air speeds less than 14 m/s.

[0066] The Sample B fabric performed well at low speeds, having a drag coefficient Cd of less than 0.80 at air speeds between 6 m/s and 8 m/s, but less well at higher speeds, the drag coefficient exceeding 1.00 at air speeds of more than 16 m/s.

[0067] The new Sample F fabric with a gradually varying texture height performed well across a wide range of speeds, having a drag coefficient Cd of less than 1.00 at speeds above 8 m/s and a drag coefficient Cd of less than 0.80 at speeds between 10 m/s and 25 m/s.

[0068] The new Sample C, Sample D and Sample E fabrics were all comparable with the Sample F fabric and performed well across a wide range of speeds, particularly in the crucial 5-20 m/s speed range. All three had a drag coefficient Cd of less than 1.00 at speeds above 8.5 m/s and a drag coefficient Cd of less than 0.82 at speeds between 10 m/s and 25 m/s, the Sample E fabric performing slightly better than the Sample c and Sample D fabrics at speeds below 9 m/s, and not quite so well at speeds above 11 m/s.

[0069] Therefore, neither of the prior art Sample A and Sample B fabrics provided a low drag coefficient across the entire 5 m/s to 20 m/s speed range, the Sample A fabric providing low drag only at high speeds between 16 m/s and 25 m/s, and the Sample B fabric providing low drag only at relatively slow speeds between 6 m/s and 10 m/s.

[0070] By comparison the three new constant height fabrics (Samples C, D and E) provided a much wider range of low drag performance, all providing a drag coefficient of less than 1.00 at air speeds above 9 m/s, and less than 0.82 at air speeds between 11 m/s and 25 m/s.

[0071] In FIG. 2b the wind tunnel test results are illustrated for a plain 130 mm radius cylinder and for four different fabrics on a 130 mm radius cylinder, the fabrics being as follows: [0072] Sample Aa prior art textured fabric that performs best at high speeds; [0073] Sample Ba prior art textured fabric that performs best at low speeds; [0074] Sample Ca new fabric comprising an embodiment of the invention, having a silicone chevron texture pattern with a spacing of 7 mm and a constant texture height of 0.4 mm; [0075] Sample Da new fabric of the type described in EP16165668.1, which does not comprise an embodiment of the invention, having a silicone chevron texture pattern with a spacing of 7 mm and a texture height that increases gradually from 0.5 mm to 5.0 mm (the portion with the smallest texture height being positioned on the front part of the cylinder).

[0076] The fabrics were each wrapped around the circumference of the 130 mm radius cylinder for the test.

[0077] As can be seen in FIG. 2b, the prior art Sample A fabric again performed well at high speeds, having a drag coefficient of less than 0.60 at air speeds between about 14 m/s and 20 m/s, but less well at lower speeds, the drag coefficient rising rapidly to a value in excess of 1.00 at air speeds less than about 12 m/s.

[0078] The Sample B fabric performed well at low speeds, having a drag coefficient of less than 0.80 at an air speed of about 5 m/s, but less well at higher speeds, the drag coefficient exceeding 0.88 at air speeds of more than 10 m/s.

[0079] The Sample D fabric with a gradually varying texture height performed well across a wide range of speeds, having a drag coefficient of less than 1.00 at speeds above 6 m/s and a drag coefficient of less than 0.80 at speeds between 8 m/s and 25 m/s.

[0080] However, the Sample C fabric performed even better than the Sample D fabric across the entire 5-20 m/s speed range, having a drag coefficient of less than 1.00 at speeds above 5.5 m/s and a drag coefficient of less than 0.80 at speeds between 7 m/s and 25 m/s.

[0081] As a result of these and other tests we have identified the following advantageous characteristics in relation to a low drag garment that is designed to provide a low drag coefficient across a range of relative speeds including in particular the range 5-20 m/s: [0082] the garment comprises a textured fabric in at least a side region of the garment, wherein the textured fabric has a texture pattern with a substantially uniform texture height in the range 0.2-0.8 mm, preferably 0.3-0.7 mm, more preferably 0.4-0.6 mm. [0083] the garment includes a body portion, and the textured fabric is provided in at least one side region of the body portion, wherein the textured fabric in the side region of the body portion has a texture pattern with a substantially uniform texture height in the range 0.2-0.4 mm. [0084] the garment includes a sleeve portion and the textured fabric is provided in at least one side region of the sleeve portion, wherein the textured fabric in the side region of the sleeve portion has a texture pattern with a substantially uniform texture height in the range 0.3-0.8 mm, preferably 0.4-0.6 mm. [0085] the garment includes a leg portion and the textured fabric is provided in at least one side region of the leg portion, and wherein the textured fabric in the side region of the leg portion has a texture pattern with a substantially uniform texture height in the range 0.2-0.4 mm. [0086] the garment additionally comprises a relatively smooth fabric in at least one front region of the garment, wherein the relatively smooth fabric has a texture height of less than 0.2 mm, preferably less than 0.1 mm. [0087] the garment additionally comprises a textured fabric in at least one rear region of the garment, wherein the textured fabric in the rear region of the garment has a texture height of at least 0.4 mm, preferably at least 0.5 mm. [0088] the side region of the garment comprises a region of the garment in which the surface angle has a minimum value .sub.1 in the range 5 to 45, preferably 10 to 25, and a maximum value .sub.2 in the range 95-160, preferably 105-140. [0089] the texture pattern 8 comprises a plurality of isolated texture formations 8a separated by regions with substantially no surface texture. [0090] the texture formations 8a are arranged in rows 10 that extend transverse to the direction of air flow, preferably with a mean spacing between the rows in the range 1 mm to 10 mm, more preferably 2 mm to 8 mm.

[0091] The garment may include any one or a combination of the preferred characteristics set out above.

[0092] We have found that in certain embodiments the textured fabric 3 covering the surface of a cylindrical body 2 can be divided into a number of zones including a front zone A, a side zone B and a rear zone C, which are defined in relation to the direction of forward movement M, as shown in FIG. 1. The first zone A is located generally in an inner front region of the cylindrical body 2, the side zone B is located generally in an outer region of the cylindrical body 2, and the rear zone C is located generally in a rear region of the cylindrical body 2.

[0093] In the front zone A the fabric may be relatively smooth, having a texture height HA of less 0.2 mm, to minimise friction drag.

[0094] In the side zone B the texture pattern preferably has a height H.sub.B in the range 0.2-0.8 mm, more preferably 0.2-0.4 mm in a body portion of the garment, 0.4-0.8 mm in a sleeve portion and 0.2-0.4 mm in a leg portion.

[0095] In the rear zone C the texture pattern preferably has a height H.sub.C that is at least as great as that in the side zone B, and may be greater to further reduce pressure drag.

[0096] The side zone B may be defined as comprising the region of the textured fabric in which the surface angle has a minimum value .sub.1 in the range 5 to 45, preferably 10 to 25, and a maximum value .sub.2 in the range 95-160, preferably 105-140. The front zone A and the rear zone C comprise the remaining portions of the textured fabric.

[0097] The texture pattern 8 can take various different forms, an example being illustrated in FIGS. 3-5. The texture pattern illustrated in FIGS. 3-5 comprises a staggered array of chevron-shaped texture formations 8a, which are arranged in transverse rows 10 with a mean separation D between the rows in the direction of air flow typically in the range 1 mm to 10 mm, preferably 2 mm to 8 mm. The mean separation G between the texture formations 8a that form each row 10 in a direction perpendicular to the direction of air flow is typically in the range 1 mm to 6 mm, preferably 2 mm to 4 mm. The height of the texture pattern corresponds to the height H of the formations 8a. The chevron-shaped texture formations 8a are preferably arranged to point in the expected direction of airflow over the surface.

[0098] In this embodiment the texture pattern 8 comprises a plurality of isolated texture formations 8a, which are separated by regions with substantially no surface texture. We have found that isolated texture formations, separated by areas of fabric with substantially no surface texture, provide reduced surface drag as compared to fabrics with continuous texture formations, as well as reduced pressure drag.

[0099] It should be noted that the exemplary texture pattern illustrated in FIGS. 3-5 is only one example of the many different patterns that may be used.

[0100] In the case of a garment made from a textured fabric, the texture pattern 8 may for example be provided by using a jacquard knitted fabric. Alternatively, the texture pattern can be printed onto the fabric or it can be created by applying a suitable solid material, for example silicone, to the surface of the fabric. The silicone may for example be applied to the surface of the fabric using a 3D printer.

[0101] The garment is preferably an article of sports clothing, which may be used for any sport where the reduction of drag is important. This applies particularly to sports where the input power is limited (for example being supplied by the athlete or the force of gravity) and where the athlete travels at a speed typically in the range 5-20 m/sec, for example cycling, running, speed skating or skiing. The article of clothing may for example consist of a shirt, trousers, leggings, shorts, bibshorts, shoes, overshoes, arm covers, calf guards, gloves, socks or a one-piece bodysuit. The article of clothing may also be an item of headwear, for example a hat or helmet, or a fabric covering for a helmet.

[0102] An example of a garment intended for use while cycling is illustrated in FIGS. 6 and 7. The garment in this case is a one-piece bodysuit 11 comprising a body portion 12 that covers the athlete's trunk, with short sleeves 14 and legs 16 that cover the upper portions of the athlete's arms and legs. The garment has a plurality of zones that are defined in relation to the direction of forward travel M of the athlete, and which take account of the athlete's posture. The zones include a first zone A located generally in an inner front region of the garment, a second zone B located in a side region of the garment and a third zone C that is located in a rear region of the garment. The outer surface of the garment has a texture that varies across the three zones, the fabric being essentially smooth in the first zone A (e.g. having a height less than 0.2 mm), have a height of 0.2-0.8 mm in the second zone B, and a height in third zone C that is either equal to or greater than that in the side region 8.

[0103] In this example, the first zone A is located primarily on the chest and shoulder regions of the trunk 12 and on the forward facing portions of the sleeves 14 and the legs 16. The second zone B is located primarily on the side and back regions of the body 12 and on the side regions of the sleeves 14 and the legs 16. The third zone C is located primarily on the lower back portion of the body 12 and the rear portions of the sleeves 14 and the legs 16. This arrangement of texture patterns has been found to be particularly advantageous for cyclists adopting the classic crouched posture illustrated in FIGS. 6 & 7. It will be appreciated that in other sports where the athletes adopt different postures, the arrangement of the texture patterns will be adapted as required to provide a low level of pressure drag.