Experiments on transient growth of turbulent spots

Klotz, Lukasz; Wesfreid, José Eduardo

doi:10.1017/jfm.2017.614

Cited by 22 publications

(21 citation statements)

References 38 publications

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“…The mechanism is similar to that proposed by Hall and co-workers [25][26][27] and by Beaume and co-workers [28][29][30]. Experimental evidence for the SSP in plane boundary layer and channel flow has been reported by Wesfreid and colleagues in [31,32]. These experiments show a strong correlation between the growth of rolls and the presence of waves: both phenomena occur above the same Reynolds-number threshold.…”

supporting

confidence: 86%

Self-sustaining process in Taylor-Couette flow

et al. 2018

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The transition from Tayor vortex flow to wavy-vortex flow is revisited. The Self-Sustaining Process (SSP) of Waleffe [Phys. Fluids 9, 883-900 (1997)] proposes that a key ingredient in transition to turbulence in wall-bounded shear flows is a three-step process involving rolls advecting streamwise velocity, leading to streaks which become unstable to a wavy perturbation whose nonlinear interaction with itself feeds the rolls. We investigate this process in Taylor-Couette flow. The instability of Taylor-vortex flow to wavy-vortex flow, a process which is the inspiration for the second phase of the SSP, is shown to be caused by the streaks, with the rolls playing a negligible role, as predicted by Jones [J. Fluid Mech. 157, 135-162 (1985)] and demonstrated by Martinand et al. [Phys. Fluids 26, 094102 (2014)]. In the third phase of the SSP, the nonlinear interaction of the waves with themselves reinforces the rolls. We show this both quantitatively and qualitatively, identifying physical regions in which this reinforcement is strongest, and also demonstrate that this nonlinear interaction depletes the streaks.

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confidence: 86%

Self-sustaining process in Taylor-Couette flow

et al. 2018

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“…(13) with boundary condition given by Eq. (16). The Poisson equation accepts a homogeneous solution p H satisfying ∇ 2 p H = 0, and an inhomogeneous solution p I such that ∇ 2 p I satisfies Eq.…”

Section: Solution For the Pressure In The Time-splitting Forward Eulementioning

confidence: 99%

Fourier continuation method for incompressible fluids with boundaries

Fontana

Bruno

Mininni

et al. 2020

Computer Physics Communications

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We present a Fourier Continuation-based parallel pseudospectral method for incompressible fluids in cuboid non-periodic domains. The method produces dispersionless and dissipationless derivatives with fast spectral convergence inside the domain, and with very high order convergence at the boundaries. Incompressibility is imposed by solving a Poisson equation for the pressure. Being Fourier-based, the method allows for fast computation of spectral transforms. It is compatible with uniform grids (although refined or nested meshes can also be implemented), which in turn allows for explicit time integration at sufficiently high Reynolds numbers. Using a new parallel code named SPECTER we illustrate the method with two problems: channel flow, and plane Rayleigh-Bénard convection under the Boussinesq approximation. In both cases the method yields results compatible with previous studies using other high-order numerical methods, with mild requirements on the time step for stability.

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“…[15], which are exactly the same as Eqs. (39) and (40) above, while the new Eq. (41) for the cross-correlation has been obtained following the same techniques.…”

Section: Appendix A: Calculation In the Absence Of Boundary Conditionmentioning

confidence: 99%

“…2, integration of Eqs. (39), (43), and (44) for ϵℝ E yields the diagonal elements of ⟨ ⟩ <= in real space and for large Re. As an example, we consider here the computation of II • .…”

Section: Appendix A: Calculation In the Absence Of Boundary Conditionmentioning

confidence: 99%

Nonequilibrium Casimir pressures in liquids under shear

2019

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In stationary nonequilibrium states coupling between hydrodynamic modes causes thermal fluctuations to become long ranged inducing nonequilibrium Casimir pressures. Here we consider nonequilibrium Casimir pressures induced in liquids by a velocity gradient. Specifically, we have obtained explicit expressions for the magnitude of the shear-induced pressure enhancements in a liquid layer between two horizontal plates that complete and correct results previously presented in the literature. In contrast to nonequilibrium Casimir pressures induced by a temperature or concentration gradient, we find that in shear nonequilibrium contributions from short-range fluctuations are no longer negligible. In addition, it is noted that currently available computer simulations of model fluids in shear observe effects from molecular correlations at nanoscales that have a different physical origin and do not probe shear-induced pressures resulting from coupling of long-wavelength hydrodynamic modes. Even more importantly, we find that in actual experimental conditions, shear-induced pressure enhancements are caused by viscous heating and not by thermal velocity fluctuations. Hence, isothermal computer simulations are irrelevant for the interpretation of experimental shear-induced pressure enhancements.

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Experiments on transient growth of turbulent spots

Cited by 22 publications

References 38 publications

Self-sustaining process in Taylor-Couette flow

Self-sustaining process in Taylor-Couette flow

Fourier continuation method for incompressible fluids with boundaries

Nonequilibrium Casimir pressures in liquids under shear

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