9 results found
Biancofiore L, Gallaire F, Heifetz E, 2015, Interaction between counterpropagating Rossby waves and capillary waves in planar shear flows, Physics of Fluids, Vol: 27, ISSN: 1070-6631
A counterintuitive destabilizing effect of the surface tension in planar wakes has been observed by Tammisola et al. ["Effect of surface tension on global modes of confined wake flows," Phys. Fluids 23, 014108 (2011)] and Biancofiore et al. ["Direct numerical simulations of two-phase immiscible wakes," Fluid Dyn. Res. 46, 041409 (2014)] by means of linear global analyses and direct numerical simulations, respectively. In the present study, we approximate the velocity profile of a wake flow through a piecewise broken-line profile and explain the presence of temporal unstable modes using an interfacial wave interaction perspective. With this perspective, we associate to each vorticity discontinuity an individual counterpropagating Rossby wave (RW), while the introduction of a finite amount of surface tension at the interface creates two capillary waves (CWs) which propagate with respect to the interface velocity with the same relative velocity but in opposite directions. The addition of the surface tension generates a new unstable mode, which is a Rossby-capillary mode, since it is due to the interaction between one RW and one CW. Furthermore, we capture the spatio-temporal evolution of the interacting four-waves system by means of an impulse response analysis. The spreading of the wavepacket, and consequently the absolute nature of the instability, is enhanced by a moderate surface tension, especially if the interface is located close to the faster edge of the broken-line wake profile. This can be explained by the influence of the surface tension on the group velocities of the waves, taken in isolation.
Biancofiore L, Gallaire F, Laure P, et al., 2014, Direct numerical simulations of two-phase immiscible wakes, Fluid Dynamics Research, Vol: 46, ISSN: 0169-5983
Tammisola et al (2012 J. Fluid Mech. 713 632-58) have observed a counter-intuitive destabilizing effect of the surface tension in planar wakes by means of a global linear analysis. In the present study, we conduct direct numerical simulation (DNS) of wakes of two immiscible fluids. The numerical scheme is based on a level set approach to track the interface position. We simulate both sinuous and varicose perturbations of wake flows. DNS confirms a destabilization on the sinuous perturbations in presence of a moderate amount of the surface tension, while wakes are stabilized when the surface tension is further increased. Varicose perturbations present in contrast an intermittent low-amplitude oscillatory regime which does not significantly affect the position of the interface. © 2014 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.
Biancofiore L, 2014, Crossover between two- and three-dimensional turbulence in spatial mixing layers, Journal of Fluid Mechanics, Vol: 745, Pages: 164-179, ISSN: 0022-1120
We investigate how the domain depth affects the turbulent behaviour in spatially developing mixing layers by means of large-eddy simulations based on a spectral vanishing viscosity technique. Analyses of spectra of the vertical velocity, of Lumley's diagrams, of the turbulent kinetic energy and of the vortex stretching show that a two-dimensional behaviour of the turbulence is promoted in spatial mixing layers by constricting the fluid motion in one direction. This finding is in agreement with previous works on turbulent systems constrained by a geometric anisotropy, pioneered by Smith, Chasnov & Waleffe (Phys. Rev. Lett., vol. 77, 1996, pp. 2467-2470). We observe that the growth of the momentum thickness along the streamwise direction is damped in a confined domain. An almost fully two-dimensional turbulent behaviour is observed when the momentum thickness is of the same order of magnitude as the confining scale.
Biancofiore L, Gallaire F, 2012, Counterpropagating Rossby waves in confined plane wakes., Phys Fluids (1994), Vol: 24, ISSN: 1070-6631
In the present work, we revisit the temporal and the spatio-temporal stability of confined plane wakes under the perspective of the counterpropagating Rossby waves (CRWs). Within the context of broken line velocity profiles, each vorticity discontinuity can be associated to a counterpropagating Rossby wave. In the case of a wake modeled by a broken line profile, the interaction of two CRWs is shown to originate in a shear instability. Following this description, we first recover the stability results obtained by Juniper [J. Fluid Mech. 590, 163-185 (2007)]10.1017/S0022112007007975 and Biancofiore and Gallaire [Phys. Fluids 23, 034103 (2011)]10.1063/1.3554764 by means of the classical normal mode analysis. In this manner, we propose an explanation of the stabilizing influence of the confinement on the temporal stability properties. The CRW description further allows us to propose a new interpretation of the counterintuitive spatio-temporal destabilization in wake flows at moderate confinement noticed by Juniper [J. Fluid Mech. 565, 171-195 (2006)]10.1017/S0022112006001558: it is well predicted by the mean group velocity of the uncoupled CRWs.
Biancofiore L, Gallaire F, Pasquetti R, 2012, Influence of confinement on obstacle-free turbulent wakes, Computers & Fluids, Vol: 58, Pages: 27-44, ISSN: 0045-7930
Biancofiore L, Gallaire F, Pasquetti R, 2011, Large eddy simulations of confined turbulent wake flows, Journal of Physics: Conference Series, Vol: 318, Pages: 042044-042044
Biancofiore L, Gallaire F, Pasquetti R, 2011, Influence of confinement on a two-dimensional wake, JOURNAL OF FLUID MECHANICS, Vol: 688, Pages: 297-320, ISSN: 0022-1120
Biancofiore L, Gallaire F, 2011, The influence of shear layer thickness on the stability of confined two-dimensional wakes, PHYSICS OF FLUIDS, Vol: 23, ISSN: 1070-6631
Biancofiore L, Gallaire F, 2010, Influence of confinement on temporal stability of plane jets and wakes, PHYSICS OF FLUIDS, Vol: 22, ISSN: 1070-6631
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