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The underbody of a truck is responsible for an appreciable portion of the vehicle’s aerodynamic drag, and thus its fuel consumption. This paper investigates experimentally the flow around side-skirts, a common underbody aerodynamic device which is known to be effective at reducing vehicle drag. A full, 1/10 scale European truck model is used. The chassis of the model is designed to represent one that would be found on a typical trailer, and is fully reconfigurable. Testing is carried out in a water towing tank, which allows the correct establishment of the ground flow and rotating wheels. Optical access into the underbody is possible through the clear working section of the facility. Stereoscopic and planar Particle Image Velocimetry (PIV) set-ups are used to provide both qualitative images of and quantitative information on the flow field.

The turbulent wake behind a truck is responsible for a considerable proportion of the total aerodynamic drag. There is evidence to suggest that the underbody flow affects the wake topology, although this interaction is not well understood. Typical truck trailer underbodies are geometrically very complex and have a range of bluff bodies - such as the wheel and axle assembly, structural beams or the secondary fuel tank for refrigerated trucks - attached. These components block the underbody flow and erode its momentum. However, most of the previous studies of the wake flow have used models with clean underbodies. It is thus uncertain whether the wake shapes found by these studies accurately represent the wake topology behind a real truck with a detailed underbody.