Title: Characterisation of the flow past real road vehicles with blunt afterbodies

Authors: Mathieu Grandemange; D. Ricot; C. Vartanian; T. Ruiz; O. Cadot

Addresses: Unité de Mécanique, Ecole Nationale Supérieure de Techniques Avancées, ParisTech, Chemin de la Hunière, 91761 Palaiseau Cedex, France; PSA Peugeot Citroën, Centre Technique de Velizy, Route de Gisy, 78943 Vélizy-Villacoublay Cedex, France ' Renault, Technocentre, 1 avenue du Golf, 78288 Guyancourt Cedex, France ' GIE S2A, Souffleries Aéroacoustiques Automobiles, 2 avenue Volta, 78180 Montigny Le Bretonneux, France ' PSA Peugeot Citroën, Centre Technique de Velizy, Route de Gisy, 78943 Vélizy-Villacoublay Cedex, France ' Unité de Mécanique, Ecole Nationale Supérieure de Techniques Avancées, ParisTech, Chemin de la Hunière, 91761 Palaiseau Cedex, France

Abstract: The flows past two different road vehicles with blunt after-bodies are studied at Reynolds numbers 107. The boundary layer thickness and the pressure distribution around the body are characterised. Then, the wake is investigated through static pressure and velocity measurements. Similar properties are obtained for both vehicles; in particular the lowest pressure on the afterbody is reported on the lower part of the base. Hot-wire anemometry is also used to depict the dynamics of the flow. The detached shear from the roof behaves as free shear turbulent flows whereas the flow from the underbody rather corresponds to homogeneous shear turbulent flows. In addition, global mode dynamics is reported in the wake of one vehicle and is associated with an antisymmetric coupling of the lateral mixing layers. However, the intensity of this mode is limited and its maximum of amplitude is downstream of the recirculation bubble; therefore it may not be a contributor to the drag. Eventually, these results are analysed to orient future drag reduction control strategies.

Keywords: road vehicle aerodynamics; separated flows; three-dimensional wake dynamics; full-scale experiments; drag sources; 3D wake dynamics; blunt afterbodies; road vehicles; boundary layer thickness; pressure distribution; static pressure; velocity measurement; shear turbulent flow; flow dynamics; drag reduction.

DOI: 10.1504/IJAD.2014.057797

International Journal of Aerodynamics, 2014 Vol.4 No.1/2, pp.24 - 42

Available online: 12 Jul 2013 *

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