This paper presents the work carried out by Applus+ IDIADA on the effect that trailer drag reducing devices have on the overall truck aerodynamic performance, as well as proving the applicability and feasibility of Computational Fluid Dynamics (CFD) as alternative approach to Constant Speed Testing (CST) when predicting the changes in CDxA [m2]. Out of all possible solutions for reducing aerodynamic resistance on semitrailers, boat tails and side skirts seem to be the most popular devices nowadays. Other potential drag reduction devices such as vortex generators, trailer diffusers or trailer undertrays have also been identified and are not rare in other markets with a more mature regulation regarding CO2 emissions, such as the United States. For starters, simple and non-commercial shapes mimicking a 400mm boat tail and a short version of trailer side skirts, covering only the side ride protection bars, were manufactured and tested at the IDIADA Proving Ground facilities according to the test procedure described in Annex 8 of the Commission Regulation (EU) 2017/2400 of 12 December 2017. The vehicle configuration consisted of an IVECO Stralis equipped with their Hi-Way Cabin from 2016 and a standard semitrailer “ST1” manufactured by Schmitz Cargobull. In total, four different configurations were tested, consisting of the standard configuration (C00) and its variants: Boat tail (C01), side skirts (C02) and both devices mounted together (C03). This later configuration was also used to identify potential effects when mounting more than one device at a time. Parallel to the experimental approach, the corresponding virtual 3D models were built and simulated with the commercial code STAR-CCM+® by SIEMENS following two different strategies: steady-state and transient approaches. This work shows the potential of virtual tools, such as CFD, proving the accuracy in which not only changes in aerodynamic resistance are predicted, but also absolute drag coefficient values and, as a consequence, opening the door to potential future virtual homologation processes.
Ing. Albert Gascón-Vallbona, Applus+ IDIADA, SPAIN Ing. Marc Soler Aldea, Applus+ IDIADA, SPAIN