On-Road Vehicle Aerodynamics with the Ring-of-Fire Concept
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This paper presents the first full-scale particle image velocimetry(PIV) measurements to analyze the complete flow field of acar under real driving conditions. The Ring of Fire (RoF) measurementconcept, introduced by Terra et al. (Exp Fluids 58:83, 2017https://doi.org/10.1007/s00348-017-2331-0), is adapted to automotive demandsto validate CFD simulations for further improvements of vehicle aerodynamics.The experiment consists of a tunnel setup, where neutrally buoyant helium-filledsoap bubbles are used as flow tracers and are illuminated by two high-speedlasers; four high-speed cameras captured the particles motion in two separateStereo-PIV-configurations with fields of view of 1.3ˆ0.6m2 and 2.8ˆ2.2m2.Data for a Volkswagen up!, while driving on a test track at a constant speed of33.33 m/s was acquired and processed with standard multi-pass PIV algorithms,in order to quantify the flow field and estimate limits of the described measurementprinciple for on-road car aerodynamics. The resulting velocity fieldsare compared with CFD-simulations, showing agreement for the here consideredcases within 9.65 - 6.97%, based on the root-mean-square error betweenthe experimental and the numerical results. Furthermore, drag calculation fromthe obtained velocity fields based on moment conservation is performed andthe percent difference to wind tunnel measurements reaches values below 3.0%.
