Analysis on the influence of gap flow around a tractor-trailer

Abstract

With the booming of electronic commerce and logistics industry, tractor-trailers play an increasingly important role in transport industry. However, as tractor-trailers are large consumers of energy, this issue arouses the attention of scholars and manufacturers to reduce their energy consumption due to the global energy crisis. For tractor-trailers, aerodynamic drag accounts for a large proportion of total resistance, thus reduction of aerodynamic drag is an efficient energy-saving method. Among various kinds of aerodynamic drag, the gap flow between truck and trailer has a relatively large impact, which has attracted people’s attention. Due to the great differences in structures and sizes of trucks, it is of great significance to find out the optimal gap between truck head and carriage to get the best aerodynamic characteristics. This paper aims to explore the optimum gap of each model and analyze the mechanisms and laws of the flow. The Ahmed reference model was established, without considering other factors, such as wheels, wing mirrors and so on. The grid division was done with ICEM software. By comparing the CFD numerical simulation results in ANSYS FLUENT with the wind tunnel experiment, the established model was evidenced to be correct and reliable. Three typical tractor-trailers were chosen and simplified as models with different area ratios of truck and trailer. The turbulent flow around models was investigated with LES (Large Eddy Simulation) model to discuss the influence on aerodynamic characteristics caused by gap between truck and trailer. It is indicated by the research that there was a best gap for minimal coefficient of drag (𝐶") about per model. In conclusion, when the height of trucks does not exceed that of trailers, it has the minimal 𝐶"when the area ratio is close to one. The relationship among gap, 𝐶"and area ratio provides a meaningful reference for the design of trucks in efficiently reducing fuel consumption and greenhouse gas emission.