Forced wakes far from threshold

Forced wakes far from threshold: Stuart–Landau equation applied to experimental data
S. Boury, B. Thiria, R. Godoy-Diana, G. Artana, J. E. Wesfreid, and J. D’Adamo
Physical Review Fluids 3, 091901(R) (2018)

We studied with the Stuart-Landau (SL) amplitude equation, a wake flow control scenario using experimental data from a cylinder wake forced by plasma actuators. Given the formal framework recently discussed by Gallaire et al. [Fluid Dyn. Res. 48, 061401 (2016)] on pushing amplitude equations far from threshold, we analyze experimental data of a forced wake in order to test the SL reduced order model. Linear stability theory and global mode concepts are used to determine the SL parameters. The extension to forced wakes of the SL model had been proposed by Thira and Wesfreid [J. Fluid Mech. 579, 137 (2007)] in the context of their study on stability properties, but its employment still remained an open question. Here, we show that a forced wake at a Reynolds number far from the first threshold can also attain the critical behavior described by the SL model.

Centrifugal instability of Stokes layers in crossflow

centrifugal_instability_cylinderCentrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake
J. D’Adamo, R. Godoy-Diana & J. E. Wesfreid
Proceedings of the Royal Society A 471: 20150011 (2015).

A circular cylinder oscillating in a viscous fluid produces an axisymmetric Stokes layer, a fundamental flow susceptible to centrifugal instabilities [see e.g. Seminara & Hall, Proc. Roy. Soc. London A 350, 299 (1976)]. In the present work we study such problem in the wake flow around a circular cylinder at Re = 100 performing rotary oscillations. Continue reading “Centrifugal instability of Stokes layers in crossflow”

Spatiotemporal spectral analysis of a forced cylinder wake

spectral_analysisSpatiotemporal spectral analysis of a forced cylinder wake
J. D’Adamo; R. Godoy-Diana & J. E. Wesfreid.
Physical Review E, 84 : 056308 (2011).

Abstract: The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at $Re=100$. Two-dimensional particle image velocimetry on the mid-plane perpendicular to the axis of cylinder is used to characterize the spatial development of the flow and its stability properties. Continue reading “Spatiotemporal spectral analysis of a forced cylinder wake”

Impulse response in the subcritical cylinder wake

impulse_cylinder_wakeConvective instability in inhomogeneous media: impulse response in the subcritical cylinder wake
C. Marais; R. Godoy-Diana; D. Barkley & J. E. Wesfreid.
Physics of Fluids, 23 (1): 014104 (2011).

Abstract: We study experimentally the impulse response of a cylinder wake below the critical Reynolds number of the Bénard-von Kármán instability. In this subcritical regime, a localized inhomogeneous region of convective instability exists which causes initial perturbations to be transiently amplified. The aim of this work is to quantify the evolution resulting from this convective instability using two-dimensional particle image velocimetry in a hydrodynamic tunnel experiment. Continue reading “Impulse response in the subcritical cylinder wake”