Aerodynamic drag control by pulsed jets on simpliﬁed car
Received: 13 January 2012 / Revised: 27 December 2012 / Accepted: 5 January 2013 / Published online: 31 January 2013
Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Aerodynamic drag control by pulsed jets is tested
in a wind tunnel around a simpliﬁed car geometry named
Ahmed body with a rearslant angle of 35°. Pulsed jet actuators
are located 5 9 10
m from the top of the rear window.
These actuators are produced by a pressure difference ranging
from 1.5 to 6.5 9 10
Pa. Their excitation frequency can vary
between 10 and 550 Hz. The analysis of the control effects is
based on wall visualizations, aerodynamic drag coefﬁcient
measurements, and the velocity ﬁelds obtained by 2D PIV
measurements. The maximum drag reduction is 20 % and is
obtained for the excitation frequency F
= 500 Hz and for the
pressure difference DP = 1.5 9 10
Pa. This result is linked
with a substantial reduction in the transverse development of
the longitudinal vortex structures coming from the left and
right lateral sides of the rear window, with a displacement of
the vortex centers downstream and with a decrease in the
transverse rotational absolute values of these structures.
Nowadays, many applied and fundamental studies are devo-
ted to aerodynamic drag reduction for road and aeronautical
vehicles. The goal is to reduce the foreign trade deﬁcit by
decreasing a purchase of fuel and/or to reduce pollutant gas
emissions and the greenhouse effect when the energy used is
fossil fuel. In the automotive domain, the objective consists in
reducing petrol consumption and also in increasing the
autonomy of electric cars by extending their use beyond urban
Studies have been performed in recent years in order to
characterize and to control the ﬂow separation at the back
of bluff bodies with or without a slanted rear window.
These conﬁgurations represent the geometry of road vehi-
cles. Signiﬁcant drag reduction can be obtained thanks to
the expertize developed in the last 30 years. Solutions such
as longitudinal (Lanser et al. 1991) or transversal (Gillie
and Kourta 2010) separated splitter plates have been pro-
posed. Flaps (Beaudoin and Aider 2008) or vortex gener-
ators (Pujal et al. 2010) can also be a solution in order to
reduce separation and to improve drag reduction. Many
designers, however, are reluctant to implement these
solutions. The current objective therefore is to search for a
new way to reach the deﬁned goal without modifying the
external car geometry. Control by using ﬂuid actuators
such as steady blowing or suction, alternating blowing and
suction, and pulsed or synthetic jets is a new solution that
can satisfy both designers and researchers (Pernod et al.
2009; Aubrun et al. 2011). This technique consists in
blowing or suction from small-sized distributed oriﬁces.
The actuators have to be lightweight and compact.
Numerous techniques have been explored to control the
ﬂow separation either by preventing it or by reducing its
effects. These methods can be efﬁcient when using active
control devices either steady or unsteady (synthetic jets,
acoustic excitation) (Beaudoin et al. 2004; Roume
as et al.
as 2006; Pastoor et al. 2008; Joseph et al.
2012). Continuous (Aubrun et al. 2011), pulsed (Joseph
This article is part of the collection Topics in Flow Control. Guest
Editors J. P. Bonnet and L. Cattafesta.
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Exp Fluids (2013) 54:1457