Abstract
Heavy goods vehicles are an integral part of road cargo transportation and carried 85% of Europe's road freight in 2018. Many investigations have been carried out on different HGV aerodynamic devices to make them more fuel-efficient and reduce emissions. Cab Roof Deflectors (CRD) placed on tractor roofs are one of those devices used to guide the incoming flow on the roof of the trailer. Most HGVs have a mismatch in the heights of the tractor and trailer such that a largely exposed tractor face causes increased fuel consumption and turbulence in the gap area between tractor and trailer. The changing flow velocity and direction, however, require further research to find the optimum position at different flow conditions. This study has used computational fluid dynamics numerical modelling technique to investigate different relative velocities and yaw angles. It was found that the conventional way of adjusting the CRD in such a manner that it matches the height of the trailer, does not provide maximum fuel efficiency. Further investigations have revealed that there is not one fixed optimum position of the CRD, and it requires an active flow control system to adjust the position according to surrounding conditions. It was also found that the efficiency of the CRD was greatly reduced in strong crosswind conditions and requires adjustment to a different optimum position. This study has achieved an extra 7 to 13% fuel saving by adjusting the CRD to its different optimum positions according to the wind conditions.