Development of a Budget Roof Fairing Using a CFD Analysis of Different Roof Fairing Shapes

Abstract

Semi-trailer trucks are commonly used in Sri Lanka for long distance transportation. These trucks are subjected to an unfavourable high drag which makes a huge impact in fuel consumption. In order to reduce this drag, semi-trailer truck cabins are implemented with a roof fairing which provides a perfect air flow over the entire vehicle. Purpose of this research was to evaluate the efficiency in drag reduction of different roof fairing shapes by conducting a computational fluid dynamics (CFD) analysis. Simulations were done on a 1:1 scaled semi-trailer truck model which was modelled using the blueprint of a commonly used truck model in Sri Lanka. Initial simulation was done without the roof fairing and results were compared with the values of coefficient of drag provided by the manufacturer to improve the accuracy of the research. Different roof fairing shapes were then modelled and attached to above mentioned cabin model and CFD simulations were performed. Subsequent simulations were done using three truck speeds which were 30, 60 and 100 kilometres per hour. The efficiency of each roof fairing was analysed during the post-processing phase after the estimation of the coefficient of drag values. Effect of other coefficients such as coefficient of lift and moment were also considered during the analysis. Results which were achieved through the simulations illustrated a drag reduction excess of 10-25% due to the impact of the geometry and the deflection angles of the roof fairing. Based on the analysis, an effective roof fairing shape was proposed which can be manufactured at a lower cost compared to the roof fairing shapes that are available in Sri Lanka. Final outcomes of this research will be helpful for designers to design more effective roof fairings for semitrailer trucks with improved drag reduction.