A study of wake effects on the drag of Ahmed super(3)s squareback model at the industrial scale

• Published in: Journal of wind engineering and industrial aerodynamics 2015-10, Vol.145, p.282-291
• Main Authors: Grandemange, M, Cadot, O, Courbois, A, Herbert, V, Ricot, D, Ruiz, T, Vigneron, R
• Format: Article
• Language: English
• Subjects: Aerodynamics; Angles (geometry); Chamfering; Computational fluid dynamics; Drag; Drag reduction; Fluid flow; Yaw
• ISSN: 0167-6105
• DOI: 10.1016/j.jweia.2015.03.004

Experiments are performed at industrial scales over the Ahmed geometry, i.e. at a Reynolds number of based on the height of the body. The shape of the squareback geometry is first optimized 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 of 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 plus or minus 0.5 degree 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, et al., 2012). The suppression of the bi-stable behavior using a passive control technique is associated with an additional drag reduction of 1.6%.