Patent Application
20220410985
The present invention relates to a vehicle, and in particular to a tractor-trailer where the trailer is adapted to reduce aerodynamic drag.
Heavy goods vehicles (HGVs) comprising a tractor and a trailer are responsible for approximately 17% of the UK's transport CO2 emissions. At motorway speeds up to 50% of the fuel consumed by a vehicle is used to overcome aerodynamic drag. At the rear of the HGV trailer, separation from the blunt trailing edges forms a large wake immediately behind the vehicle which produces lower pressures that act to resist the vehicle's motion. The rear of the trailer is responsible for 30-35% of the total vehicle drag.
Boat-tail designs for reducing drag are well known (Saltzman, E. and Jr. R. Meyer (1999—A Reassessment of Heavy-Duty Truck Aerodynamic Design Features and Priorities. California: NASA National Technical Information Service). However, these are largely impractical due to the difficulty of loading and unloading a vehicle fitted with such a device through more restricted access to the rear doors. There are also difficulties with the structural integrity of such attachments. In addition, safety and regulatory concerns exist over the stability of vehicles when fitted with these devices.
Over the years there have been many varied designs of panels attached to the rear of trailers with a view to reducing drag. All of these devices suffer from the same issues as above to varying degrees, e.g.: example as seen in U.S. Pat. No. 9,855,982 (a vertical member of the rear frame to extend generally rearward of the trailer) and US 2014/0239669 (a flap that extends from the roof over the end of the trailer). Rejniak, A.A. and Gatto, A. (2019) Application of Lobed Mixers to Reduce Drag of Boat-Tailed Ground Vehicles. Journal of Applied Fluid Mechanics, Vol. 12, No. 6, pp. 1729-1744 describes the use of lobed mixers within a boat-tail as an add-on device to a trailer so that the device protrudes from the base of trailer.
Vortex generators can also be added to the sides of the vehicle in this area (Lay, C. (2013)—Three Dimensional CFD Analysis on Aerodynamic Drag Reduction of a Bluff Tractor Trailer Body using Vortex Generators. 2013 Commercial Vehicles Engineering Congress, p. 10). They work on the principle of mixing enhancement to delay flow separation and therefore achieve drag reduction (Wood, R. M. (2006)—A Discussion of a Heavy Truck Advanced Aerodynamic Trailer System. SOLUS-Solutions and Technologies LLC). The effect of these are relatively small (1-5% fuel savings) but have been used in combination with truncated tail boats to improve drag reduction (e.g.: U.S. Pat. No. 6,959,958). However, these vortex generation devices normally develop high induced drag, reducing their effectiveness.
EP 0272998 A2 (United Technologies Corp.) discloses a projectile having a downstream extending surface of revolution which terminates as a blunt base which has a plurality of circumferentially spaced apart U-shaped downstream extending troughs in its surface. Each trough is essentially aligned with the direction of the bulk fluid flow adjacent the surface in the vicinity of the trough, and intersects the blunt base to form a trough outlet therein. The troughs are appropriately spaced apart, sized and configured over their entire length causing fluid to flow into the space immediately behind the blunt base, thereby reducing base drag on the projectile.
DE 102012010002 A1 (Daimler AG) discloses an invention which is based on a wind deflector for a commercial vehicle, in particular for a semi-trailer with an air guidance system which has at least one air guidance element arranged at a rear to reduce the air resistance of the commercial vehicle. It is proposed that the air guiding element arranged at the rear be designed as a diffuser and that the air guiding system have an aerodynamic inflow body as a further air guiding element which is matched to the diffuser.
In accordance with a first aspect of the invention, there is provided a vehicle including:
In a preferred embodiment, p1>p2. It will be appreciated that p2 is a continuous variable in the range 0<p2<p/2. However, in a preferred embodiment p2 is less than or equal to p/4.
Surprisingly, it has been found that providing side channels which are asymmetric (in that, preferably, the trough of the channel is closer to the top of the vehicle than the bottom) results in an improved drag coefficient (compared to symmetric channels), as does providing a pitched roof channel (compared to a flat roof). Furthermore, the combination of asymmetric side channels and a pitched roof channel gives even better results.
The side walls can in one embodiment include more than one channel, and the values of peaks and troughs of the plurality of channels may be irregular in shape, with the value of h varying and/or the value of p, p1 and p2 varying. Ideally however the two side walls have an identical configuration of channels and are identical or closely similar in configuration so that the drag on each side of the vehicle is broadly symmetrical.
In a preferred embodiment, the vehicle is a combination of a tractor and trailer. It could however be a powered vehicle such as a bus or a train or a boat or a car.
The inventive arrangement has the advantage that it does not protrude over the existing base of the vehicle and so avoids any concerns over vehicle stability and safety or structural integrity of the design. It is instead embedded in the vehicle itself so there are no significant safety and regulatory disadvantages. There is also the added advantage that it does not interfere with the loading and unloading of the vehicle.
In accordance with an alternative aspect of the invention, there is provided a vehicle including:
A preferred embodiment of the invention will now be described with reference to and as illustrated in the accompanying drawings, in which:
Turning to
In the illustrated embodiment, the side walls of trailer 10 are modified to each include a single channel 20. The roof is modified to include two roof channels 30, one on either side of a single roof peak 32 forming a ridge 31 of length L′ as will be described below. The trailer floor is unmodified to allow for unimpeded loading of goods into trailer 10. A trailer door or ramp may be attached to bottom edge 14 (not shown).
Channels 20 each have front end 21 and rear end 22 with length L. Each of channels 20 is shallow at the front end 21 and deeper at rear end 22, so that the floor of each channel 20 is angled away from the plane of the trailer wall at angle α. Each channel has an opening 23 at side edge 13.
The width of each channel 20 from peak-to-peak is labelled p on
For symmetric channels (not in accordance with the invention) p1=p2 and this is illustrated in (a)(i) in
Turning to
The profile of the roof at roof edge 15 where it meets rear end 12 is best seen from
Roof peak 32 is in the centre of the roof and is at the same height as the roofline and at the end of ridge 31 proximate roof edge 15. The end of each roof channel 30 distal to roof edge 15 is at the same height as the roofline and so the line forming the trough of each roof channel 30 along its length L′ is at an angle α′ to the roofline.
In an alternative embodiment (not shown) each side wall may include more than one channel in which case the profile of the channel openings at side edge 13 form a series of peaks and troughs.
Preferred ranges for angle α height h, width p and length L are given in Table 1 below:
More preferred ranges for angle α, height h, width p and length L are given in Table 2 below:
In use, tractor 5 is driven to tow trailer 10 behind it. Air flowing down the trailer side walls enters each channel 20 at front end 21, flow down length L of channel 20, and exits channel 20 at rear end 22 through channel opening 23.
Air flowing along the pitched roof profile flows along roof channels 30 and exits at roof edge 15.
In an alternative embodiment, channels 20 and 30 may be embedded into the walls and roof of a driven vehicle such as a bus or boat or train or car.
A simplified 1/24th-scale model as illustrated in
The drag force, in Newtons, was measured for both the baseline vehicle without any channels and for the modified vehicle with channels embedded. All measurements were repeated three times to assess variability.
The baseline drag coefficient, Cdbaseline, for the vehicle (without channels) is calculated as:
and the drag coefficient for the modified vehicle, Cd, is calculated as:
Where,
Dbaseline=Drag force of baseline vehicle without channels, N
D=Drag force of baseline vehicle with channels, N
ρ=air density, kg/m3
V=flow velocity, m/s
S=Vehicle frontal area, m2
Results can be reported as either the absolute drag coefficient, Cd, or as the change in drag coefficient,
Results
In Examples 1 to 5 the effect of the design is demonstrated for α=20°. As shown in Example 1, a reduction in drag coefficient, −ΔCd, of 9.7% is achieved when a single asymmetrical channel (p2=p/4) is embedded on both sides of the trailer with a peak roof. This can be compared to Example 2 where a single symmetrical channel (p2=p/2) is embedded on both sides of the trailer with a peak roof and a reduction in drag coefficient, −ΔCd, of only 7.4% is achieved.
The contribution of each of the channels embedded in the top and sides of the trailer can also be seen. As shown in Example 4, a reduction in drag coefficient, −ΔCd, of 4.9% is achieved when a single asymmetrical channel (p2=p/4) is embedded on both sides of the trailer with no peak roof. This can be compared to Example 5 where a single symmetrical channel (p2=p/2) is embedded on both sides of the trailer with no peak roof and a reduction in drag coefficient, −ΔCd, of only 3.2% is achieved.
The effect of the combination of the designs for the two sides and the roof are seen by comparison of Examples 3 and 4 with Example 1. The simple addition of the designs on the roof in Example 3 and the sides only in Example 4 would predict a reduction in drag coefficient, −ΔCd, of 6.7%. However, this combined design as measured in Example 1 gives a reduction in drag coefficient, −ΔCd, of 9.7% thereby demonstrating the surprisingly increased benefit of combining the roof and sides designs.
In Examples 6-12 the effect of effect of the angle α=25° is demonstrated. As shown in Example 6, a reduction in drag coefficient, −ΔCd, of 6.5% is achieved when a single asymmetrical channel (p2=5p/6) is embedded on both sides of the trailer with a peak roof. This can be compared to Example 7 where a single symmetrical channel (p2=p/2) is embedded on both sides of the trailer with a peak roof and a reduction in drag coefficient, −ΔCd, of only 4.5% is achieved.
The contribution of each of the channels embedded in the top and sides of the trailer can also be seen. As shown in Example 9, a reduction in drag coefficient, −ΔCd, of 1.8% is achieved when a single asymmetrical channel (p2=5p/6) is embedded on both sides of the trailer with no peak roof. This can be compared to Example 10 where a single symmetrical channel (p2=p/2) is embedded on both sides of the trailer with no peak roof and a reduction in drag coefficient, −ΔCd, of only 0.7% is achieved.
The effect of the combination of the designs for the two sides and the roof are seen by comparison of Examples 8 and 9 with Example 6. The simple addition of the designs on the roof in Example 8 and the sides only in Example 9 would predict a reduction in drag coefficient, −ΔCd, of 4.2%. However, this combined design as measured in Example 6 gives a reduction in drag coefficient, −ΔCd, of 6.5% thereby demonstrating the surprisingly increased benefit of combining the sides and roof designs.
As shown in Example 11, a reduction in drag coefficient, −ΔCd, of 5.0% is achieved when a single asymmetrical channel (p2=p/4) is embedded on both sides of the trailer with a peak roof. This can be compared again to Example 7 where a single symmetrical channel (p2=p/2) is embedded on both sides of the trailer with a peak roof and a reduction in drag coefficient, −ΔCd, of only 4.5% is achieved.
The contribution of each of the channels embedded in the top and sides of the trailer can also be seen. As shown in Example 12, a reduction in drag coefficient, −ΔCd, of 2.2% is achieved when a single asymmetrical channel (p2=p/4) is embedded on both sides of the trailer with no peak roof. This can be again compared to Example 10 where a single symmetrical channel (p2=p/2) is embedded on both sides of the trailer with no peak roof and a reduction in drag coefficient, −ΔCd, of only 0.7% is achieved.
The effect of the combination of the designs for the two sides and the roof are seen by comparison of Examples 8 and 12 with Example 11. The simple addition of the designs on the roof in Example 8 and the sides only in Example 12 would predict a reduction in drag coefficient, −ΔCd, of 4.6%. However, this combined design as measured in Example 11 gives a reduction in drag coefficient, −ΔCd, of 5.0% thereby demonstrating the surprisingly increased benefit of combining the sides and roof designs.
All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.
The disclosures in UK patent application number 1917653.6, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1917653.6 | Dec 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2020/053091 | 12/2/2020 | WO |
