Analysis of Drag Reduction Using Aerodynamic Devices on Commercial Buses by Computational Fluid Dynamic Simulation

Abstract

A large percentage of the usable fuel employed in a commercial bus is utilized to overcome the aerodynamic drag at highway speeds and therefore if reduced could produce a large reduction in the total fuel consumption of the vehicle and reduce the negative environmental effects. MCI's D4505 coach bus was modeled in this study and airvanes, drag reduction devices, were employed on the model bus to reduce the drag coefficient of the bus. Each airvane, attached to edges of the leeward face of the bus, was optimized by a parameter study were each individual dimension of the device was tested to determine the optimal design. The airflow surrounding the bus models with and without the airvanes attached were modeled using a computational fluid dynamics software. In this software different turbulence models and meshes were employed to observe the effect of these changes on the predicted airflow and optimization of the aerodynamic devices. Two separate sets of simulations were run on each dimension tested. The first simulation utilized a polyhedral mesh with the Realizable k-ε turbulence model, while the second set of simulations used a CutCell mesh and the Shear Stress Transport k-ω turbulence model. It was found that to reach a maximum reduction of the drag coefficient of the bus airvanes were placed on all edges of the leeward face and optimized for the specific placement on the bus. A drag coefficient of 0.54351 was produced which was a reduction of 12.37% for the polyhedral RKE model while the CutCell SST model produced a drag coefficient of 0.54021 a reduction of 14.55%. This reduction in the drag coefficient lead to a maximum reduction of 1.5% in the fuel consumption, which if applied to all commercial buses would have a significant effect on the total national fuel consumption and a positive impact on the environment.