Experimental aerodynamic study of a car-type bluff body

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Experimental aerodynamic study of a car-type bluff body

Conan, Boris / Anthoine, Jerome / Planquart, Philippe

The aerodynamics of a car-type bluff body was investigated through the so-called Ahmed body. Drag coefficient measurements were performed within the VKI-L1 wind tunnel using an open and closed test sections. A very good sign of the reproducibility and the reliability of the results is the matching between the tests realized in the open and closed test sections. Less than 0.5 % of difference proves an independence of the test section and the quality of the data that can be obtained in the wind tunnel. However, some differences are observed between the VKI results and original data from Ahmed. Differences of around 12 % are present, they might be due to geometrical difference on the model or on the floor. Unfortunately, definitive conclusions cannot be set because complete comparison with the original data is limited by the lack of precise information on the literature: model roughness, detailed frontal geometry or precise oncoming boundary layer. The physical understanding of the flow behaviour around the rear of the model was analysed by various types of measurement techniques. The combination of two complementary techniques like oil visualization and PIV is very helpful specially in the low drag configuration of the 30 rear angle. More challenging to set-up, PIV has the other great advantage of giving information on the unsteadiness structure of the flow, something not possible with averaging techniques like oil visualization.