The flow-field around a "common" European heavy truck, equipped with several different trailer devices, is investigated using steady and unsteady simulations. This work demonstrates how with simple devices added on the trailer it is possible to strongly decrease the aerodynamic drag over 10%, with an increase of overall dimensions below 1% without any change to the load capacity of the trailer. Several devices, installed on the trailer, are tested on a target vehicle and the shape of the "airbag", the "fin", the "boat tail" and the "front-rear trailer device" has been optimized to achieve the maximum in drag reduction in front wind. The performance of the optimized devices are tested also in cross wind conditions with the yaw angle varying from 0° to 30°. The truck equipped with the front-rear trailer device is also investigated using time variant simulation with yaw angle of 0°, 5°, 10°. Detached eddy simulation (DES) with one equation Spalart-Allmaras as turbulence model is used to perform the analysis of the unsteady flow; the two equation k-ω SST turbulence model is selected for the steady-state RANS simulations. The unsteady simulations are performed using computational meshes on the order of 40 million of elements while RANS simulation are done with mesh of 10 million of elements. The analysis is performed in the open-source CFD framework OpenFOAM.
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