Flow around an articulated lorry model

•The flow physics over an articulated vehicle was investigated experimentally.•Both time-averaged and instantaneous flow fields are presented.•Shear layer flapping is observed in the instantaneous flow field.•The flapping is caused by the shear layer and wake vortex interaction.•Detailed quantitative data measured in the wake region are provided. 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 counter-clockwise 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.