Aerodynamic analysis of a car-trailer combination using CFD based numerical techniques: A shape optimisation and drag reduction study

The concept of towable horse trailers and caravans has become increasingly common for transporting horses around the country as well as for providing a comfortable and mobile living space during vacations. It is very common for the towing vehicle to double its fuel usage by towing a horse trailer or a caravan. The massive increase in fuel consumption is mainly due to the changed aerodynamics. To optimise the design of the trailer and reduce fuel consumption, it is essential to know the high drag contribution surfaces and appropriately modifying them. In the present study, two different industrial models of the horse-trailer have been evaluated and optimised for their aerodynamic drag. Both trailers have a different front design which can represent almost all-important feature changes to estimate the drag contribution and prediction of the best-optimised shape. The challenge is to reduce the drag force without reducing the internal accommodation space and meeting the legal specifications. The front shape of the trailer, roof and different add-on devices has been tested and drag performance has been evaluated. The length of the wake region has been improved by providing a roof curvature and diffuser at the top and bottom rear side of the trailer. Providing a roof curvature on the trailer roof has delayed the flow separation at the rear end of the roof by reducing the adverse pressure gradients. The wake behind the car is found sensitive to the gap between the car and trailer. Adverse pressure gradient has been recovered in the wake region by using add-on devices. This resulted in the conclusion that fuel consumption has been reduced to a significant percentage.