A study of wake effects on the drag of the Ahmed’s squareback model at the industrial scale
Abstract
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%.
Origin : Files produced by the author(s)
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