GB2513540A

GB2513540A - Device for improving aerodynamics of vehicles

Info

Publication number: GB2513540A
Application number: GB1302214.0A
Authority: GB
Inventors: Ashwyn Dhir
Original assignee: Swift Group Ltd
Current assignee: Swift Group Ltd
Priority date: 2013-02-08
Filing date: 2013-02-08
Publication date: 2014-11-05
Also published as: GB201302214D0

Abstract

A device to manipulate a fluid flow around a towed vehicle 200 comprises a deflecting member 300 and an attachment portion. The attachment portion is configured to attach the deflecting member proximate a front side edge 212/214 of the towed vehicle. The deflecting member is configured to control flow around the front side edge of the vehicle, such that a wake extending from the side of the vehicle is reduced. The flow may be delayed in separating from the side of the vehicle. The device may be integral or removable from the vehicle, and may be designed to extend around a portion of the front side edge of the vehicle. The device may be in the shape of a tear drop aerofoil. There may be a gap of between 2-30cm between the device and the towed vehicle, defining a duct with an inlet and outlet, wherein the inlet may be 20%-50% larger than the outlet. There may be another device positioned on the same front side edge of the towed vehicle. The towed vehicle may be a caravan.

Description

DEVICE FOR IMPROVING AERODYNAMICS OF VEHICLES

FIELD OF INVENTION

The invention relates to apparatus for improving the aerodynamics of a vehicle. More particularly, the invention relates to apparatus for improving the aerodynamics of a towed vehicle, such as a caravan.

BACKGROUND OF THE INVENTION

Caravans are not particularly efficient when towed. This is due to their high weight relative to the towing vehicle, rolling resistance from tyres, and their large size and shape. The latter contributes to a high aerodynamic drag, which comprises, skin friction drag and principally the pressure drag. Consequently, the vehicle used to tow the caravan expends a large amount of fuel during towing.

Historically, aerodynamic studies of flow around caravans have been considered unnecessary since it is generally accepted that the wake from the towing vehicle encompasses the flow around the caravan. Therefore, it is considered more effective to attach components upstream of the rear of the towing vehicle, such as deflectors or diffusers to control the wake, rather than attempt to optimise the shape of the caravan.

An object of the present invention is to provide a caravan which overcomes one of the above or other problems. More specifically, an object of the present invention is to provide a towed vehicle which is more efficient to tow.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a device to manipulate a fluid flow around a vehicle, the device comprising: a deflecting member and an attachment portion, wherein the attachment portion is configured to attach the deflecting member proximate a front side edge of the towed vehicle, and the deflecting member is configured to manipulate a position of a portion of the flow travelling into the front surface of the vehicle such that it is redirected onto a side of the vehicle to thereby control flow around the front side edge such that a wake extending from the side of the vehicle is reduced.

By undertaking numerical modelling of the flow around a caravan the inventors have found that, contrary to conventional opinion, and at normal towing velocities, the wake of the flow from the tow vehicle is in general resolved before the flow reaches the caravan.

Accordingly, and contrary to the current technical prejudice, it has been found that substantial aerodynamic improvements can be made by optimising the shape of the caravan.

More particularly it has been found that on a conventional caravan, a portion of the free stream flow that travels above and around the towing vehicle is deflected such that it travels into the front face of the caravan where it causes high drag. A portion of this flow is diffused around the top and sides of the caravan. Generally, the top front edge of the caravan is curved such that the flow is able to smoothly transition from the front to top. However, the front side edged of the caravan are generally sharply angled with minimum curvature. This is because it is it undesirable to curve these edges since such curvature would reduce the occupiable interior space of the caravan. Accordingly, as the flow travels around this the front side edge, the flow is unable to be turned which results in flow separation and a consequent region of wake which extends outwardly from the front side edge. Such an effect is undesirable since it results in high drag.

Accordingly, the invention solves the first objective by reducing the quantity of wake that extends from the front side edge, or alternatively put, by delaying flow separation on the sides, which reduced the drag of the caravan.

Preferably, the vehicle is a caravan or motorhome or trailer.

Preferably, the deflecting member is configured to reduce the size of the wake which extends from the side of the vehicle, in a position proximate the front side edge of the vehicle.

Preferably, the device is operable to reduce the volume of the wake which extends proximate the front side edge of the vehicle. Preferably, the device is operable to reduce the extent of the wake which extends from the side of the vehicle, when preferably measured along a line normal to the side of the caravan.

Preferably, the deflecting member is configured to delay separation of flow around the front side edge of the caravan such that it preferably occurs further downstream, wherein separation preferably occurs as the flow travelling along the surface of the vehicle is detached from the surface of the vehicle.

Preferably, the deflecting member is configured to transition a portion of the flow travelling over the front face towards the side face through an angle of about 90° -450 Preferably, the deflecting member is configured to smooth a portion of the edge between the front and side of the vehicle.

Preferably, the deflecting member is configured such that at least part of the flow flowing over it attaches to the side of the vehicle without separation.

Preferably, the attachment portion is configured to attach the device to one or more of the top, front and sides of the vehicle. Optionally, the attachment portion comprises a removable attachment comprising fixing means such as bolts. Optionally, the attachment portion is formed integrally with part of the vehicle, such as the body work or other structural member.

Preferably, the deflecting member comprises a first control surface which is arranged to extend around a portion of the front of the vehicle. Preferably, first control surface is configured to extend a long at least part of the side of the vehicle. Preferably, first control surface is configured to extend around a portion of the front side edge of the vehicle.

Preferably, the first control surface comprises a first end and second end, wherein the first end is preferably positioned to extend over at least part of the front face and the second end is preferably positioned to extend over at least part the side face. Accordingly, the first end is arranged upstream of the second end.

Preferably, the first control surface extends around at least part of the front side edge from a leading edge to a trailing edge to provide a guide that re-directs flow travelling on to the front face to the side face.

The first control surface is optionally shaped in the form of an aerofoil, wherein the aerofoil shape comprises a tear drop shape having a rounded leading edge at the first end, followed by a sharp trailing edge at the second end. Preferably, the aerofoil is cambered, wherein the camber line is curved such that it extends around at least part of the front side edge of the towed vehicle. Optionally, the curvature of an inner surface of the control surface is greater than that at the adjacent point an outer surface of the control surface, more preferably, it is at least 10% greater.

Alternatively, the first control surface is in the form of a substantially flat plate, which curves around at least part between the first and second end.

Optionally, the leading edge at the first end, and I or the trailing edge at the second end are arranged to be substantially parallel to the front side edge. Optionally, the leading edge at the first end is angled with respect to the front side edge, such that it is closer to the front side edge at an upper edge rather than a lower edge.

Preferably, first control surface is configured such that the leading edge is a horizontal distance of between 2 -30cm from an adjacent portion of the front face of the towed vehicle, more preferably it is about 10cm. Preferably, the distance between the leading edge of the control surface and the adjacent portion of the top surface defines an inlet, the inlet being arranged to ingest a portion of flow that travels into the front face.

Preferably, first control surface is configured such that the trailing edge is a horizontal distance of between 2-30cm from an adjacent portion of the side face of the towed vehicle, more preferably it is about 10cm. Preferably, the distance between the trailing edge of the control surface and the adjacent portion of the side surface defines an outlet, the outlet being arranged to outlet the flow ingested by the inlet.

Preferably, the outlet and inlet are arranged such that in angle of the outlet flow is about go° -453 of that of in inlet flow, when measured in relation to the free stream direction.

Optionally, the cross sectional area of the outlet is substantially the same as the inlet.

Optionally, the cross sectional area of the inlet is about 20 -50% greater than that of the outlet.

Preferably, the first control surface is configured such that, when positioned on the towed vehicle, a lower surface of the control surface and surface of the towed vehicle, which extends around the front side edge, defines duct for transmission of flow, which extends from the inlet to the outlet.

Preferably, the radii of curvature of an inner surface of the control surface is greater than that at the adjacent point on the rear edge of the vehicle, more preferably, it is at least 10% greater. Preferably, the curvature is through an angle of between about 60 -135°. More preferably, the radius of curvature adjacent the side edge is between about Scm -20cm.

Preferably, the first control surface is arranged to smoothly transition flow travelling proximate the front face of the vehicle, to the side face of the vehicle.

Preferably, the leading edge overlaps the front face such that the overlap region extends a horizontal distance of about 10 -50 cm from the front side edge. Preferably, the trailing edge overlaps the side face such that the overlap region extends a horizontal distance of about 10 - 50cm from the front side edge.

Preferably, the first control surface comprise an apex, which is defined as furthest point in a width direction from the central axis of the caravan, the apex being positioned between the first and second end, wherein the second end is positioned a lesser width from the central axis of the caravan. Such that the first control surface tucks back in form the apex. In this way flow traveling through the duct is guided back onto the side face.

Preferably, the upper edge and lower edge of the first control surface extend such that they are substantially parallel to each other. More preferably, they are spaced apart by a distance of about 10cm -70cm. More preferably, they are about 20cm apart.

Preferably, the lower edge of the device is positioned at a height of between 10-30% of the vertical distance from the bottom to the top of the vehicle, when measured from the bottom surface of the vehicle.

Additionally, or alternatively further device may be positioned on the same edge, the device being arranged such that the lower edge is positioned at a height of between 40 -80 % of the vertical distance from the bottom to the top of the vehicle, when measured from the bottom surface of the vehicle.

Optionally, the deflecting member further comprises a second control surface, which is configured to abut side face proximate the front side edge of the towed vehicle, the second control surface being shaped to extend into the dud to control expansion of flow within the duct. Preferably the second control surface is configured to increase the effective radii of the front side edge, such that the flow travelling within the duct is gradually turned to delay/prevent separation of the flow travelling around the front side edge.

Preferably, the second control surface is configured to extend into the duct such that a constant distance is maintained between an outer surface of the second control surface and the inner surface of the first control surface.

Preferably, the deflecting member is configured to manipulate flow at conventional vehicle velocities, such as 20-120 KM/H.

Preferably, the device is made from one or more or the following, or a similar material; ABS, GRP, Nylon, ASA.

According to a second aspect of the invention there is provided a vehicle comprising one or more of the devices as described according to the first aspect of the invention.

According to a third aspect of the present invention there is provided a method of manipulate flow around a towed vehicle, the method comprising: interacting a deflecting member of a device with a portion of the flow travelling into the front surface of the vehicle such that it is redirected onto a side of the vehicle to thereby control flow around the front side edge such that the wake extending from the side of the vehicle is reduced.

All of the features described herein may be combined with any of the above aspects, in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 shows a perspective view of a prior art caravan; Figure 2 shows a top cross-sectional view of fluid flow around a prior art caravan; Figure 3 shows a perspective view of a device to manipulate flow around a caravan according to a first aspect of the invention; Figure 4 shows a perspective view of the caravan of figure 2 with the device of figure 3 attached; Figure 5 shows a top cross-sectional view of fluid flow around the caravan of figure 4 at a cross-sectional height such that the device of figure 3 is intersected, the height of the cross-section being the same as that of the cross-section in figure 2;

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Figure 1 shows a perspective view of a caravan 200. Herein, the caravan 200 is defined as having a front face 210 and rear face 220, both of which are generally arranged to have a plane which is substantially perpendicular to the direction of motion of the caravan 200 (although in this embodiment the front face is shown curved to improve the aerodynamics of the caravan) and extend substantially upwardly from the ground (not shown), wherein the front face 210 is positioned upstream with respect to the rear face 220 in relation to the flow over the caravan 200 when being towed.

The caravan 200 further comprises a left side face 230 (not shown) and right side face 240, both of which extend substantially upwards from the ground, and both of which extend from the front face 210 to the rear face 220.

The caravan 200 further comprises a bottom face 250 (not shown) and top face 260.

both of which are substantially aligned to the ground, and both of which extend from the front face 210 to the rear face 220. The bottom face 250 is closest to the ground, and the top face 260 is positioned furthest from the ground.

In more detail, on one side of the front face 210 there is a left front edge 212, and on the other side there is a right front edge 214, both of which extend from a bottom to a top of the caravan 200. On one side of the rear face 220 there is a left rear edge 222 (not shown), and on the other side there is a right rear edge 224, both of which extend from a bottom to a top of the caravan 200. The left side face 230 and right side face 240 are positioned symmetrically about a centrally aligned plane 270 (not shown) of the caravan 200. The left side face 230 extends from the left front edge 212, to the left rear edge 222, and the right side face 240 extends from the right front edge 214, to right rear edge 224.

On the top of the front face 210 there is a top front edge 216, and on the bottom there is a bottom front edge 218, both of which extend in a direction which is substantially aligned to the ground and between the two side faces 230, 240. On the top of the rear face 220 there is a top rear edge 226, and on the bottom there is a bottom rear edge 228 (not shown), both of which extend in a direction which is substantially aligned to the ground and between the two side faces 230, 240. Hence the top face 260 extends from the top front edge 216 to the top rear edge 226, and the bottom face 250 extends from the bottom front edge 218 to the bottom rear edge 228.

The caravan 200 further comprises wheels 280. The wheels 280 are positioned between the bottom surface 250 and the ground and are located approximately mid-way between the front face 210 and rear face 220. In more detail the wheels 280 comprise a first wheel 282 (not shown) poisoned proximate the left side face 230, and a second wheel 284 positioned proximate the right side face 240. The wheels 282, 284 are connected by means of an axle 286 (not shown) and are arranged symmetrically about the central plane 270. The axle 286 protrudes from the bottom of the caravan 200 such that the wheels 280 extend partially into a wheel arch 288 of the bottom surface 250.

The caravan 200 yet further comprises a drawbar 290 for receiving a tow bar (not shown) of a towing vehicle, which may comprise a car or other suitable vehicle. The drawbar 290 is arranged to extend in the direction of towing from proximate the bottom front edge 218.

The caravan 200 yet further comprises a chassis 294 (not shown). The chassis 294 extends proximate the bottom face 250, and forms the main structural component of the caravan 294, to provide a rigid support for the wheels 280, drawbar 290, body panels which comprise the top, front, rear and side faces, and the framework 296 (not shown) that supports these body panels.

Figure 2 shows the flow around the front face 210, and sides 240, 230 of the caravan of figure 1 when viewed from a direction normally into the top face 260 of the caravan. By undertaking numerical modelling of the flow around the caravan the inventors have found that, contrary to conventional opinion, and at normal towing velocities, the wake of the flow from the tow vehicle is in general resolved before the flow reaches the front of the caravan. As shown in figure 2 the resultant flow travels onto and over the front face 210 of the caravan. As this flow subsequently travels over the edges 214, 212 flow separations occurs since the flow is unable to be turned such that it flows around the edge and onto the side face 240, 230. As a result flow separation is experienced along the sides of the caravan, as indicated by regions of wake 215. This is undesirable since the large wake 215 results in high drag.

Referring to figures 3 -5 an exemplary embodiment of the invention is shown, which comprises a device 100 to manipulate flow around the caravan 200. The device 100 comprises a deflecting member 300 and attachment portion 400 (not shown).

In this embodiment the attachment portion 400 comprises a bracket and fixing means (not shown) to connect the deflecting member 300 of the device 100 to the side face 240, 230 at a position which is adjacent the right front side edge 214, 212 of the caravan 200. In this embodiment the attachment portion 400 comprises part of the deflecting member, such as the upper and lower edge, which curves to abut the surface of the caravan to provide a suitable attachment point. Fixing means in the form of apertures (not shown) through which bolts are inserted secure attachment portion to the caravan 200. In other embodiments the fixing means may comprise other suitable fixings, such as an adhesive strip. Referring back to this embodiment, to remove the attachment 100 from the caravan 200, the bolts are unscrewed and removed from the apertures. Accordingly, the device 100 is removably attached to the caravan 200. In an alternative embodiment the device 100 may be formed integrally with the body of the caravan 200 such that it is not removably attached. The attachment portion 400 may be arranged to attach the device to part of the structure of the caravan, such as the body panels which comprise the front and side faces, or another structural component of the caravan.

Although only a single device has been described for convenience, as shown in figure 4, there are generally two devices 100A and bOB, one on either front side edge 214, 212 of the caravan 200.

Considering the shape of the deflecting member 300 in more detail, and with reference to figures 3 and 5: the deflecting member comprises a first control surface 301, which in this example shaped substantially in the form of an aerofoil, wherein the aerofoil form comprises a characteristic tear drop shape having a rounded leading edge 302, followed by a sharp trailing edge 304. The aerofoil is cambered, wherein the camber line is curved such that it extends around the front side edge 214, 212.

It will be appreciated that the deflecting member may be shaped in other forms, such as a flat plate, which curves around the front side edge 214, 212.

The deflecting member 300 is positioned such that the leading edge 302 is closest to the front face 210 and such that the trailing edge 304 is closest to the side face 240, 230. The distance between the leading edge 302 and side face 210 defines and inlet 306, whereas the distance between the trailing edge 304 and side face 230 defines and outlet 308. It will be appreciated that the outlet 308 expels the flow ingested by the inlet 306, as will be discussed in more detail below.

In this example the cord line (the distance between the leading end trailing edge) of the first control surface is about 50 -70 cm and the distance between the leading edge 302 and front face 201 is about 10 -20 cm, and the distance between the trailing edge 834 and rear face 220 is about 10-20 cm. The maximum thickness at the leading edge is about 3 -10 cm. Accordingly, in this embodiment, the cross sectional area of the outlet 308 is similar to that of the inlet 306, however it will be appreciated that in other embodiments one of the outlets or inlets may have a greater size than the other.

An upper edge 312 and lower edge 314 of the device 100 extend between the leading edge 302 and trailing edge 304. In this particular embodiment, the upper and lower edges are substantially parallel to each other, and are about 40 -60 cm apart.

The leading edge 302 can be angled with respect to the front side edge 214, 212, as shown in figure 4, or aligned to the front side edge 214, 212. In a similar fashion the trailing edge 304 can be angled or aligned to the front side edge 214, 212.

The deflecting member 300 further comprises an outer surface 316, and an inner surface 318, the inner surface being adjacent the surface of the front side edge 214, 212. As shown in figureS, the radii of curvature of the outer surface 318 of the deflecting member 300 generally less than that at the inner surface 318. In a preferred embodiment, it is at least 10% less.

In this embodiment, the deflecting member further comprises a second control surface 330, as best seen in figure 5. The second control surface 330 is positioned on the side face 240, 230 proximate the front side edge 214, 212. The second control surface 330 comprises a curved tip 332, which extends outwardly from the side face 240, 230 and abuts the front side edge 214, 212. The tip 332 tapers inwardly towards the side face at a trailing edge 334. The second control surface 330 extends between the upper 312 and lower 314 surfaces of the first control surface 301 In the example embodiment the front side edge 214, 212 of the caravan has a relatively sharp radius of curvature of about 2-Scm. However, it will be appreciated that the degree of curvature will vary, and therefore that the exact shape of the deflecting member 301, 330 will be optimised for the particular caravan it is intended for use with.

Generally, the deflecting member is positioned in an upper region, for instance the upper two thirds of the height of the front face 210, since this region has been found to experience a greater amount of the high energy oncoming flow. Whereas at a lower region the front face is proximate the wake from the tow vehicle. In figure 4 it is shown in a lower region.

Figure 5 shows the flow around the deflecting member 300. Notably, a portion of the flow that travels into and along the front face 210 is ingested by the inlet 306. This flow then travels through a duct defied by the inner surface 318 of the deflecting member and an outer surface 336 of the second control surface 330. As can be seen, the flow that travels along the front face is turned through about 900 such that the flow at the outlet 308 is substantially in line with the free stream flow.

In this way the ingested flow is redirected onto the side 240, 230 of the caravan, such that the size of the wake 215 (as shown in figures 2 and 3) that extends from the side face 240, 230 is reduced. It will also be appreciated that, when comparing figures 2 and 5, the device acts to control the flow such that the point of separation 213 occurs further around the front side edge 214, 212. Alternatively put, the point of separation 213 is delayed. At lower velocities, the device may also act of prevent separation on the side face 240, 230.

The second control surface 330 is arranged to maintain a more or less constant distance between its outer surface 336 and the inner surface 318 of the first control surface 301. In this way the expansion of the flow within the duct is controlled. Alternatively, put the second control surface acts to increase the effective radii of the front side edge 214, 212, such that flow traveling within the duct is gradually turned, which makes subsequent separation less likely.

As can also be seen from figure 5 that the outer surface 316 of the first control surface 301 acts to smoothly transition flow that travels onto it around the front side edge 214, 212. In this way the point of separation is delayed.

It will be appreciated that the device 100 is not restricted to use on caravans and will also be suitable for improving aerodynamics of other vehicles such as motorhomes and trailers.

It will also be appreciated that more than one device can be fitted to one of the edges 212, 214. For instance, additional devices may be fitted above and / or below the devices bOA, B. In this way the above mentioned effect can be applied to a greater proportion of the flow.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS: 1. A device to manipulate a fluid flow around a towed vehicle, the device comprising: a deflecting member and an attachment portion, wherein the attachment portion is configured to attach the deflecting member proximate a front side edge of the towed vehicle, and the deflecting member is configured to manipulate a position of a portion of the flow travelling into a front surface of the vehicle such that it is redirected onto a side of the vehicle to thereby control flow around the front side edge such that a wake extending from the side of the vehicle is reduced.
2. The device as claimed in claim 1, wherein the vehicle is a caravan or motorhome or trailer.
3. The device as claimed in any preceding claim, wherein the deflecting member is configured to reduce the size of the wake which extends from the side of the vehicle, in a position proximate the front side edge of the vehicle.
4. The device as claimed in any preceding claim, wherein the deflecting member is O configured to delay separation of flow around the front side edge of the caravan such that it preferably occurs further downstream, wherein separation occurs as the flow travelling along the surface of the vehicle is detached from the surface of the vehicle.
5. The device as claimed in any preceding claim, wherein the deflecting member is configured to transition a portion of the flow travelling over the front face towards the side face through an angle of about 9g0_450
6. The device as claimed in any preceding claim, wherein the deflecting member is configured to smooth a portion of the edge between the front and side of the vehicle.
7. The device as claimed in any preceding claim, wherein the deflecting member is configured such that at least part of the flow flowing over it attaches to the side of the vehicle without separation.
8. The device as claimed in any preceding claim, wherein the attachment portion is configured to attach the device to one or more of the top, front and sides of the vehicle.
9. The device as claimed in claim 8, wherein the attachment portion comprises a removable attachment comprising fixing means such as bolts or the attachment portion is formed integrally with part of the vehicle, such as the body work or other structural member.
10. The device as claimed in any preceding claim, wherein the deflecting member comprises a first control surface which is arranged to extend around a portion of the front of the vehicle.
11. The device as claimed in claim 10, wherein the first control surface is configured to extend around a portion of the front side edge of the vehicle.
12. The device as claimed in claim 11, wherein the first control surface comprises a first end and second end, the first end having a leading edge which is positioned to extend over at least part of the front face and the second end having a trailing edge is positioned to extend over at least part the side face, such that the first end is arranged upstream of the second end.
13. The device as claimed in claims 10, 11 and 12, wherein the first control surface is shaped in the form of an aerofoil, the aerofoil shape comprisins a tear drop shape having a rounded leading edge at the first end, followed by a sharp trailing edge at the second end.
14. The device as claimed in claim 13, wherein the aerofoil is cambered, wherein the camber line is curved such that it extends around at least part of the front side edge of the towed vehicle.
15. The device as claimed in claims 10-12, wherein the first control surface is in the form of a substantially flat plate. 4-2016. The device as claimed in claims 12-15, wherein the leading edge at the first end, and / or the trailing edge at the second end are configured to extend in a direction which is (%I,J substantially parallel to the front side edge.17. The device as claimed in claims 12-15, wherein the leading edge at the first end is angled with respect to the front side edge, such that it is closer to the front side edge at an 0 upper edge ratherthan a lower edge.18. The device as claimed in claims 12-17, wherein the first control surface is configured such that the leading edge is a horizontal distance of between 2-30cm or about 10cm from an adjacent portion of the front face of the towed vehicle and wherein the first control surface is configured such that the trailing edge is a horizontal distance of between 2 -30cm or about 10cm from an adjacent portion of the side face of the towed vehicle.19. The device as claimed in claim 18, wherein the distance between the leading edge of the first control surface and the adjacent portion of the top surface defines an inlet, the inlet being arranged to ingest a portion of flow that travels into the front face, wherein the distance between the trailing edge of the control surface and the adjacent portion of the side surface defines an outlet, the outlet being arranged to outlet the flow ingested by the inlet.20. The device as claimed in claim 19, wherein the cross sectional area of the outlet is substantially the same as the inlet.21. The device as claimed in claim 19, wherein the cross sectional area of the inlet is about 20-50% greater than that of the outlet.22. The device as claimed in claims 19-21, wherein the first control surface is configured such that, when positioned on the towed vehicle, an inner surface of the control surface and surface of the towed vehicle, which extends around the front side edge, defines a duct for transmission of flow, which extends from the inlet to the outlet.23. The device as claimed in claims 12-22, wherein the device is configured such that the leading edge overlaps the front face such that the overlap region extends a horizontal distance of about 10-50 cm from the front side edge and the trailing edge overlaps the side face such that the overlap region extends a horizontal distance of about 10 -50 cm from the front side edge.24. The device as claimed in claims 12-24, wherein the first control surface comprise an apex, which is defined as furthest point in a width direction from the central axis of the caravan, the apex being positioned between the first and second end, wherein the second end is positioned a lesser width from the central axis of the caravan, such that the first control surface tucks back in form the apex.25. The device as claimed in any preceding claim, wherein an upper edge and lower edge of the first control surface extend such that they are substantially parallel to each other.26. The device as claimed in claim 25, wherein the upper edge and lower edge are spaced apart by a distance of about 10cm -70cm.27. The device as claimed in claims 25 -26, wherein the lower edge of the device is positionable at a height of between 10 -30% of the vertical distance from the bottom to the top of the vehicle, when measured from the bottom surface of the vehicle.N-25 28. The device as claimed in any preceding claim, wherein a further device is positionable o on the same edge of the towed vehicle, the device being arrangable such that the lower edge is positioned at a height of between 40-80% of the vertical distance from the bottom to the top of the vehicle, when measured from the bottom surface of the vehicle.29. The device as claimed in claims 22 -28, wherein the deflecting member further comprises a second control surface, which is configured to abut the side face proximate the front side edge of the towed vehicle, the second control surface being shaped to extend into the duct to control expansion of flow within the duct.30. The device as claimed in claim 29, wherein the second control surface is configured to increase the effective radii of the front side edge, such that the flow travelling within the duct is gradually turned to delay/prevent separation of the flow travelling around the front side edge.31. The device as claimed in claims 29 -30, wherein the second control surface is configured to extend into the duct such that a constant distance is maintained between an outer surface of the second control surface and the inner surface of the first control surface.32. A vehicle comprising one or more of the devices as claimed in claims 1-31.33. A method of manipulating flow around a towed vehicle, the method comprising: interacting a deflecting member of a device with a portion of the flow travelling into the front surface of the vehicle such that it is redirected onto a side of the vehicle to thereby control flow around the front side edge such that the wake extending from the side of the vehicle is reduced. (4N