A study of wake effects on the drag of the Ahmed’s squareback model at the industrial scale

Mathieu Grandemange (1, 2) , Olivier Cadot (2) , Courbois, A. (2) , Vincent Herbert (1) , Denis Ricot (3) , Tony Ruiz (1) , Rémi Vigneron (4)

1 PSA - PSA Peugeot - Citroën
2 UME - Unité de Mécanique
3 Technocentre Renault [Guyancourt]
4 GIE S2A - Groupement d’Intérêt Economique Souffleries Aéroacoustiques Automobiles

Experiments are performed at industrial scales over the Ahmed geometry, i.e. at a Reynolds number of Re = 2.5×106 based on the height of the body. The shape of the squareback geometry is first optimised to make an initial substantial drag reduction. The separated flow at the trailing edge is orientated by introducing chamfers at the top and bottom edges. A parametric study based on both chamfered angles leads to an optimized Ahmed geometry having a drag 5.8% lower than the reference squareback model. It is evidenced that this optimized geometry produces 4 intense longitudinal vortices that still contribute significantly to the drag. The effect of a sideslip yaw angle is studied. As expected, it is found that the drag increases with an increase in the yaw angle, but surprisingly the drag remains constant for yaw angles within the interval ±0.5◦ for which the side force displays very large fluctuations. This plateau is explained by recent observation of the bi-stable properties of the squareback Ahmed body (Grandemange, Gohlke & Cadot, Physical Review E 86, 2012). The suppression of the bi-stable behavior using a passive control technique is associated with an additional drag reduction of 1.6%.

Domaines: Sciences de l'ingénieur [physics]; Milieux fluides et réactifs

Mathieu Grandemange, Olivier Cadot, Courbois, A., Vincent Herbert, Denis Ricot, et al.. A study of wake effects on the drag of the Ahmed’s squareback model at the industrial scale. Journal of Wind Engineering and Industrial Aerodynamics, 2015, 145, pp.282-291. ⟨hal-01205907⟩