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Aerodynamic Resources for Tractor/Trailers
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We are starting a new resource page on aerodynamic research, resources and products for the tractor/trailer for our viewers:
From the Aerospace Engineering Dpt of Netherlands UT Delft who created PART (Platform for Aerodynamic Road Transport):
Fuel Consumption:
The relative importance of aerodynamic design to reducing truck fuel consumption can be seen from an overview of the various factors involved in fuel consumption. It is important here to distinguish between different types of truck. The chart below shows the components that use energy in an articulated vehicle expressed as losses. As the chart shows, 15% of the fuel is used to overcome mechanical friction in the engine, gearbox and drive shaft. 45% of the fuel is used to overcome the rolling resistance. Drag is responsible for 40% of fuel consumption.
Drag, indicated by the letter D, is the force that the air exerts on the vehicle, which the engine has to overcome. The power needed to overcome this drag equals D · V. As the drag itself increases with the square of the travelling speed V, the power needed is proportional to the cube of the speed.
The rolling resistance, indicated by Drol, is caused by the contact between the tyres and the road. The rolling resistance can be expressed as the product of the friction coefficient μ of the tyres and the normal force N, the actual weight of the vehicle. The correlation between rolling resistance and drag depends on the speed of the vehicle and the vehicle configuration.
The correlation between fuel consumption and travelling speed is similar to the curve of overall drag. At a constant speed of 50 kmph less than 40% of the engine power is used to overcome drag, as against 60% at a speed of 80 kmph. Crosswind, interference with other traffic and weather conditions all have an effect on the aerodynamic forces that ultimately need to be overcome: these constantly changing factors increase drag.
If a truck accelerates it uses more fuel. This factor depends above all on the driving style, but also on the traffic situation and the nature of the journey. A large change in speed per unit of time yields a high acceleration a, ultimately resulting in higher energy consumption.
To follow, is Delft University's PART recommendations. (For the Cab):
This section looks at the aerodynamic aids available to reduce drag on a tractor (i.e. the motive power unit in an articulated vehicle, or the cab of a rigid vehicle or a drawbar vehicle):
Cab side-edge turning vanes
Aerodynamic side mirrors
Additional lights and horns
Air dam
Eco-flaps
Side panels
Hub caps
Chassis filler panel
Sun visor
Roof fairing or deflector
Collar with roof fairing
Tractor side panels
Base bleed
(For the Container):
This section looks at the container portion of the vehicle, i.e. the semi-trailer of an articulated vehicle or the body of a rigid vehicle and any trailer. The performance figures for the aerodynamic aids are based on various studies and experiments carried out by a variety of research organisations and universities. It should be noted that the fuel savings stated in this section for a drawbar vehicle relate to the motor vehicle, not the trailer. Any fuel savings from fitting aerodynamic aids to a trailer towed by a rigid vehicle are mentioned separately.
Fairing
Vortex stabilisers
Teardrop roof
Sloping roof
Rotating cylinders
Flatbed container
Side panels
Wedge
High-momentum mud flaps
Airwedge
Aerodynamic under-body
Rear mud flap
Underride guard
Boat tail
Inset boat tail
SDR
Vanes
Vortex generators
Vortex strakes
Blowing slots
For more information, please go to: http://www.part20.eu/en/
From the SimCenter for Riverbend Technologies at UTC in Chattanooga, TN:
Computational Simulations of Airflows Related to Class-8 Trucks and Affecting Fuel Economy and Exhaust Emissions
These simulations involve very complex flow patterns about very complex vehicle geometries, and they require the leading-edge capabilities of the SimCenter’s Tenasi code for high-resolution of unsteady turbulent three-dimensional flows.
Full-scale simulations of airflow past a Class-8 truck showing the effect of different mudflap designs on the aerodynamic drag force coefficient. These results show that mudflap design has an important influence on aerodynamic drag and hence fuel economy and exhaust emissions. (Sponsored by Riverbend Technology Institute, John Schaerer)
Full-scale Simulation of airflow past a Class-8 truck showing the effect of aerodynamic drag reduction devices such as trailer splitter plates and base flaps. These results show how these devices affect the very complex flow patterns on the downwind side of a truck traveling in a cross wind at nine degrees to the direction of travel. (Sponsored by Riverbend Technology Institute, John Schaerer)
Comparison of SimCenter Tenasi flow simulations and experimental data taken at NASA’s 7 ft. by 10 ft. wind tunnel. These comparisons show that the computational flow simulations give accurate predictions of pressure distributions affecting aerodynamic drag and hence fuel economy and exhaust emissions. (Sponsored by the Department of Energy: National Transportation Research Center, Oak Ridge National Laboratory, and Lawrence Livermore National Laboratory)
SimCenter flow simulation of past an isolated rotating wheel on a roadbed, showing the complex three-dimensional viscous contact jet generated where the rolling wheel contacts the roadbed. The excellent agreement with experimental measurements validates this capability of the Tenasi code. (Sponsored by the Department of Energy: National Transportation Research Center, Oak Ridge National Laboratory, and Lawrence Livermore National Laboratory)
Flow Simulations for complex flow patterns past complex vehicle geometries require very advanced geometric modeling and grid generation algorithms and software. The SimCenter is a leader in unstructured grid generation technology for viscous flow simulations. Shown here are some examples of grids generated for several complex vehicle geometries using the SimCenter’s HUGG grid-generation software system. (Sponsored by the Tennessee Higher Education Commission Center of Excellence for Applied Computational Science and Engineering at UTC)
From our New England Distributor, with the help of several trucking companies in their area, has comprised a helpful list of things that your fleet can do to increase your “Green Profile”. Please go to the link below for more complete details: http://blog.fleetfuelsaver.net/
- DON'T hang those trailer flaps at the ICC bar. Several fleets do this to either save money on hanger brackets, or to try to eliminate breaking flaps that are mounted directly behind the rear axle when they get caught backing up over a curb. FLAPS HUNG AT THE ICC BAR COST 0.3 TO 0.4 MPG IN FUEL ECONOMY. We've demonstrated this repeatedly this year with folks who had made equipment decisions to run this way.
- Similarly, DON'T use stiffeners to keep conventional flaps from blowing back at highway speeds. Same effect. You end up exaggerating the drag factor of the flaps, and further reducing your fuel economy.
- Trailer flaps are the most critical part of the fuel savings solution. If you can only change one thing on a rig, make sure the trailer flaps are what you swap out for fuel saving Eco-flaps. 2/3 of the overall savings from Eco-flaps get delivered by the trailer flaps.
- The more flaps you have on a rig, the greater the loss of fuel economy on the highway. We have picked up over 10% improvement in fuel economy for flatbeds, tankers, reefers, etc. that operate with 6 or more mudflaps.
- DON'T block any unnecessary portion of the undercarriage of the trailer with extra fuel tanks, air tanks, hazard signs spanning the ICC bar, deck to flap solid hanger bars, etc.. ANYTHING that blocks this air flow, especially back towards the rear of the trailer significantly pulls down fuel economy.
Crosswind Notes for Class 8 Highway Tractor/Trailers
Download: Crosswind1.pdf
Crosswind2.pdf
Crosswind3.pdf
Crosswind4.pdf
Resources:
- An article by Kevin R. Cooper of the National Research Council of
Canada. He compiled a historical perspective on aerodynamic drag
reduction for commercial vehicles, and much of the info on the impact
of yaw on the coefficient of drag came from a Trailmobile trailer
study and wind tunnel testing done by A. Wiley Sherwood at the
University of Maryland.
- Rose McCallen from Lawrence Livermore National Laboratory, who
heads up the team commissioned by the Department of Energy to reduce
aerodynamic drag on Class 8 equipment by 25% co-authored an article
that quantifies the change in MPGs as the coefficient of drag on
Class 8 equipment increases.
- Robert J. Englar from Georgia Tech also was a source of info. He
presented an SAE technical paper on advanced aerodynamic devices to
improve performance and handling of heavy vehicles, and in the paper
he detailed the effects of side winds on drag for a bunch of
different aerodynamic configurations of Class 8 tractors and trailers.
- The average wind speed data for different parts of the country
came from the US Weather Bureau's NOAA website.
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