Flow around an articulated lorry model

Keywords: Articulated vehicles Bluff bodies Road vehicle aerodynamics Square back vehicles Wake flow Wind tunnel tests a b s t r a c t An experimental study has been conducted to investigate both the time-averaged and instantaneous flow pattern over a scale articulated vehicle model for understanding the flow physics of tractor-trailer vehicles. Fully turbulent flow was used in the study and smoke visualisation, surface oil flow visualisation and two-component particle image velocimetry were employed for flow diagnostics. Results obtained from the time-averaged and instantaneous flow fields show different flow pattern in the wake region downstream of the rear end of the trailer model. In the time-averaged flow field, a single counterclockwise rotating vortex is presented in the wake region due to the coil-up of the lower shear layer. The instantaneous flow pattern shows that two wake vortices are presented in the wake region downstream of the trailer model. Moreover, the interactions between the wake vortex and the upper shear layer lead to the formation of the streamwise vortices within the shear layer. These streamwise vortices grow and propagate downstream which lead to the occurrence of vortex shedding in the upper shear layer downstream of the trailer model. Heavy Goods Vehicles (HGVs) play an important role in daily domestic goods transportation within the United Kingdom. According to the information shown in the report ''Transport Statistics Great Britain 2015 " [1], published by the Department of Transport of the United Kingdom Government, approximately 73.5% of domestic freight was transported by HGVs in 2014. In addition, about 15.5 million tonnes of greenhouse gas emissions came from HGVs. Due to the considerably poor aerodynamics efficiency of most HGVs, significant amount of fuel is consumed by HGVs to overcome the aerodynamics drag acting on the vehicles during high-speed operation. Altaf et al. [2] concluded that as much as 65% of fuel is consumed to overcome the aerodynamic drag encountered by buses and HGVs in long-haul journeys. Similarly , Bradley [3] indicated that the aerodynamic drag contributes approximately 21% of energy loss when a 36-tonne heavy goods vehicle is travelling at 105 km/h. Hsu and Davis [4] deduced that an annual fuel cost saving of US$ 10,000 could be achieved if the aerodynamic drag acting on a heavy vehicle is reduced by 40%. Similarly, Bradley [3] also anticipated that a 20% aerodynamic drag reduction on a heavy goods vehicle could lead to 4% of fuel …