Aerodynamics of heavy trucks

This project studies the aerodynamics of the HGV, focusing mainly on two important aspects: the drag reduction obtained using passive devices installed on the trailer and the wind-induced accident involving overturning and handling issue. The first topic is crucial in order to decrease the fuel consumption of the vehicle with both economic and environmental benefits. In this work, external passive devices installed on the trailer were developed and tested. The idea is to keep the internal load capacity of the trailer fixed. Front-rear trailer devices were developed as the best strategies to reduce drag, with reference to both developing and installation costs. The device reduces the aerodynamic drag around 10 %. The second topic is crucial in order to reduce wind induced accidents involving overturning when the vehicle is exposed to strong lateral wind, as when passing on viaducts or bridges. Since this phenomenon represents a serious concern for the running safety of vehicles, it has been widely investigated in literature. To increase the running safety, specific fences are occasionally placed both at the edges of bridges and close to towers, shielding vehicles from cross-wind. The design of these devices is however an extremely challenging task since it must account for the dynamic coupling of aerodynamic loads (depending on the bridge layout, i.e. deck, tower and fences) and vehicle-driver response. This work is the first step toward the validation of numerical models of aerodynamic forces acting on vehicles, used in Multi-Body simulations. It is fundamental also for the design of lateral shields to be installed on the infrastructure, and for studying the coupled driver-vehicle response during the aerodynamic interaction with the tower wake in cross wind conditions. A CFD numerical approach was developed to overcome the limitations of wind tunnel experiments using moving vehicles and dynamic mesh. The developed methodology was used in a real case to define the aerodynamic load on an HGV running on the cable-stayed bridge, designed in the “Forth Replacement Crossing” (FRC) project in Edinburgh. To mitigate wind induced accidents, in particular overturning, when the HGV is passing over long bridges or viaducts, it is possible to place lateral shield on the sides of the existing infrastructure, or it possible to optimize the aerodynamic response of the vehicle. In this work, three main ways were used and compared to optimize the aerodynamic response of the HGV:  Changing of the shape of the trailer.  Vortex Generators (VGs) installed on the leading edge of the trailer.  Front-rear trailer devices installed along the sides/top of the trailer. The first test carried out involved the change of the trailer shape making the corner between the top and the side of the trailer as smooth as possible. The performance of the rounded corner, inclined corner and corner cut were tested. All the modifications to the shape of the trailer proposed reduced the trailer load capacity. At a constant volume reduction, the rounded corner, shows a overturning moment reduction around 25 % with a limited reduction of load capacity below 1 %. VGs positioned on the top separation leading-edge, were implemented to reduce the overturning moment. Comparing the performance of the VGs with the one obtained in the previous strategy, the VGs did not seem a promising solution to mitigate the overturning risk, reducing the overturning moment no more than 2.4 %. The strategy of “adding” external passive devices onto the existing trailer was adopted. Their shape was based on the front-rear trailer device previously designed and patented by the author. This strategy seems to be the easiest one to be adopted by the “truck community;” in particular, if said device does not exceed the maximum vehicle dimension permitted by the regulation. The proposed device reduces the whole overturning moment by about 7.5 % - 8 % and whole vehicle drag around 4 %. The performance of the front-rear trailer devices installed along the sides/top of the trailer were validated with wind tunnel test on a 1:10 HGV model. The developed device has a significant influence on the HGV overturning risk reducing it about 5%-8 %, as demonstrated in the two scenarios: HGV on flat ground and HGV passing through the wake of a tower largely exposed to cross-wind.