Perspectives of Aerodynamic Drag and Cooling Airflow for Heavy-Duty Trucks - Reconsidering European Total Length Legislation

Doctoral thesis, 2016

Increasing fuel prices and constantly lowered emission legislation forces the vehicle industry to develop new methods for propelling vehicles and to optimize existing technology. Trucks constitute a significant proportion of the transportation system; consequently it is of great importance to ensure as low an impact as possible on the environment.\\[2mm] The length legislation for trucks in Europe regulates the total length of a vehicle combination, from the front of the cab to the trailing edge of the trailer. The European Cab Over Engine (COE) tractive units are, compared to the conventional designs with a hood, not preferred aerodynamically due to its flat front and relatively sharp edges. If elongating the nose of the COE cab, creating a so-called Soft Nose (SN), potential for improved aerodynamic properties is seen. To improve the transport efficiency, some countries in Europe allow vehicle combinations of up to 25.25m; the aerodynamic properties of these longer vehicles have however not been in much focus historically. This thesis deals with perspectives of aerodynamic drag and cooling airflow for heavy trucks, under the circumstances of reconsidered total length legislation. The potential for design changes of different parts of a complete truck-trailer combination have been evaluated. Computational Fluid Dynamics (CFD) was the main tool for obtaining the results; measurements have been used to verify the results.\\[2mm] The results presented in this thesis showed that there are many areas on a complete truck-trailer combination where substantial drag reductions may be acquired. It has been seen that for longer vehicle combinations, the gap between the cargo-units and the chassis level of the trailer units were large sources of drag, especially in yawed-wind conditions. By design changes of these areas, drag was reduced by significant amounts. Working with the front-end of the COE cab, an elongation of the grille area could result in both improved aerodynamic properties, but also cooling airflow can be enhanced if also considering the layout of the components in the under hood. Without a ducting system, guiding the flow from the grille towards the cooling module, or a movement of the cooling module by the same magnitude as the SN elongation, a large portion of the airflow in the under hood leaked around the cooling module and reduced cooling capacity. The main conclusion to be made is that there still are much room for aerodynamic improvements on a truck-trailer combination if reconsidering the total-length legislation. Ideally, the tractive units and trailers should be developed as a whole, to maximize the possible aerodynamic reductions.