Interaction between the near wake and the cross-section variation
of a circular cylinder in uniform ﬂow
H. Oualli Æ S. Hanchi Æ A. Bouabdellah Æ
R. Askovic Æ M. Gad-El-Hak
Received: 17 May 2006 / Revised: 27 October 2007 / Accepted: 30 October 2007 / Published online: 26 January 2008
Ó Springer-Verlag 2008
Abstract The ﬂow around a circular cylinder with a
cross-section variation is experimentally investigated.
Particle Image Velocimetry (PIV) is used to scrutinize the
interaction of the cylinder’s wall with its near wake. The
Reynolds number based on the cylinder’s diameter and
freestream velocity is 80 9 10
, corresponding to the
upper subcritical ﬂow regime. At a forcing Strouhal num-
ber of St
= 0.02, the maximum vorticity level around the
cylinder is reduced by more than 50% as compared to its
uncontrolled value. The topology of the bulk ﬂow conﬁned
between the primary vortical structure and the cylinder
surface is modiﬁed resulting in substantial drag reduction.
Coherent structures and vortex shedding in bluff body
wakes are related to several aerodynamic and hydrody-
namic practical goals, such as drag reduction, suppression
of vortex-induced vibrations—commonly known as VIV
problems, and reduction of aeroacoustic noise. Recently,
interest has been focused on the ability to control the wake
to provoke or avoid lock-in phenomenon, to increase heat
transfer or mixing and enhance combustion.
Since the pioneering work of Strouhal (1878) and Von
n(1912), a large number of studies have been
devoted to understanding ﬂows around bluff bodies and
their beneﬁcial control. A complete review of the ﬁeld will
not be possible here; for the interested reader several recent
reviews are available in the literature such as for example
papers by Coutenceau et al. (1991), Williamson (1996),
Buresti et al. (1979) and Norberg (2003), as well as the
comprehensive two-volume monograph of Zdravkovich
(1997, 2003). Gad-el-Hak (2000) exhaustively considered
the broad ﬂow control problem and the ability to manipu-
late a ﬂowﬁeld actively or passively to achieve a desired
For moderately low Reynolds numbers (Re \ 300),
several control strategies have the potential for signiﬁ-
cantly suppressing vortex shedding or altering the shedding
frequency. One such technique is to rotate the cylinder at
suitable values of amplitude and frequency (Berger 1967).
Another is to heat the cylinder wall thus changing the near-
wall ﬂuid viscosity (Wang et al. 2000). Roussopoulos
(1993) and Park et al. (1994) approached the problem
differently by employing a feedback-control strategy in
which the controlled variable is measured, fed back and
compared with a reference input value.
For Reynolds numbers greater than 300, corresponding
to the critical regime commonly known as the shear-layer
transition, predetermined active control has been attempted
via acoustic excitation using loudspeakers (Hsiao et al.
1991; Fujisawa et al. 2003), as well as by vibrating the
cylinder, streamwise oscillation and transverse oscillations
of tapered cylinders (Triantafyllou et al. 2003).
Different types of blowing are achieved by means of
synthetic jets to control the ﬂow around circular cylinders.
H. Oualli (&) Á S. Hanchi
MDF, EMP, Bordj el Bahri, Alger, Algeria
des Sciences et de la Technologie (USTHB),
LME, UVHC, 59313 Valenciennes Cedex 9, France
Virginia Commonwealth University, Richmond, VA, USA
Exp Fluids (2008) 44:807–818