CFD Analysis of Aerodynamic Trailer Devices for Drag Reduction

Today’s demand of reducing the fuel consumption of vehicles is one of the most challenging issues within the automotive industry. Together with the increased fuel price, the development of more fuel efficient vehicles has escalated. A recent research about fuel reduction technologies for trucks showed that aerodynamic improvement is one of the most important technologies when it comes to fuel saving. Volvo Trucks has a well established aerodynamic focus in the product development process of the tractor, although there are no focus on trailer aerodynamics. Therefore, more research of aerodynamics around the tractor and the trailer is desirable to see the possibilities to further reduce drag. Different aerodynamic trailer devices and aerodynamically shaped trailers have been tested by means of Computational Fluid Dynamics, in order to investigate their influence on the flow around the truck. The tests were simulated with a speed of 90 km/h, and with yaw angles of 0° and 5°. In addition, drag contribution from different regions was analyzed to see where it is possible to gain most drag. Finally, an evaluation was done to see if the results from the simulations could promote any possible aerodynamic profits of a mutual development between tractor and trailer manufacturers. The results show that the largest effects of the trailer devices are achieved during 5° yaw, this especially applies for the undercarriage treatment. Furthermore, devices that were implemented in the undercarriage and base region presented the best results, which indicates that these regions are most susceptible for drag improvements. However, it was very difficult to achieve a balanced base wake; devices placed at the rear face of the trailer improved the flow from the roof and the upper sides, whereas the air at ground level was very difficult to affect due to a disturbed undercarriage flow. The gap treatment improved the flow over the gap and along the trailer roof, although a larger gap clearance would probably have amplified the effect of these devices. Furthermore, this project has shown the importance of integrating the tractor and trailer development for further aerodynamic improvements. Profits of such mutual development can for example be that the gap could be further reduced, and the interface and flow transition between the cab, the trailer, the tractor chassis and the trailer undercarriage can be optimized