The global fuel consumption by Heavy duty vehicles is an important issue in every climate change summit. Aerodynamic drag consumes majority of fuel at highway speeds. Thus, it is important to strive hard to reduce drag using different techniques. WABCO's SideWing (side-skirt) is an air dam (aerodynamic device) placed along the sides of the trailer to prevent low and high momentum flow being mixed and eventually increase drag.

WABCO's track test data suggests that the side-skirt is under-performing in dual rear axle condition, that is in 6X4 tractor configuration. This thesis is aimed at understanding the flow physics responsible for fuel savings in single axle condition (4X2) and further extend the knowledge to 6X4 condition. In order to do so, flow physics at the front wheel (available in literature) is studied initially and validated using CFD simulations in this thesis. The side-skirt behavior is studied in single axle condition. Furthermore, the influence of rear wheel of tractor on drag and flow features is understood first. Lastly, the changes in flow features observed on the addition of an axle are understood.

The sidek-skirt showed reduced drag reduction in 6X4 condition in this thesis. This is positive trend in the sense that CFD simulation is conforms with the track test data. It is understood that the additional axle creates a under pressure region lower than compared to single axle case.