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Anisotropy and cycloneanticyclone asymmetry in decaying rotating turbulence
, 2009
"... The effect of a background rotation on the decay of homogeneous turbulence produced by a grid is experimentally investigated. Experiments have been performed in a channel mounted in the largescale ’Coriolis ’ rotating platform, and measurements have been carried out in the planes normal and paralle ..."
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The effect of a background rotation on the decay of homogeneous turbulence produced by a grid is experimentally investigated. Experiments have been performed in a channel mounted in the largescale ’Coriolis ’ rotating platform, and measurements have been carried out in the planes normal and parallel to the rotation axis using particle image velocimetry. After a short period of about 0.4 tank rotation where the energy decays as t −6/5, as in classical isotropic turbulence, the energy follows a shallower decay law compatible with t −3/5, as dimensionally expected for energy transfers governed by the linear timescale Ω −1. The crossover occurs at a Rossby number Ro ≃ 0.25, without noticeable dependence with the grid Rossby number. After this transition, anisotropy develops in the form of vertical layers where the initial vertical velocity remains trapped. These layers of nearly constant vertical velocity become thinner as they are advected and stretched by the largescale horizontal flow, producing significant horizontal gradient of vertical velocity which eventually become unstable. After the Ro ≃ 0.25 transition, the vertical vorticity field first develops a cycloneanticyclone asymmetry, reproducing the growth law of the vorticity skewness, Sω(t) ≃ (Ωt) 0.7, reported by Morize, Moisy & Rabaud [Phys. Fluids 17 (9), 095105 (2005)]. At larger time, however, the vorticity skewness decreases and eventually returns to zero. The present results indicate that the shear instability of the vertical layers contribute significantly to the resymmetrisation of the vertical vorticity at large time, by reinjecting vorticity fluctuations of random sign at small scales. These results emphasize the importance of the initial conditions in the decay of rotating turbulence. 1.
Anisotropic energy transfers in rotating turbulence
"... We investigate experimentally the anisotropic energy transfers in freely decaying turbulence subjected to a background rotation. The energy distribution E(r, t) = 〈(δu)2 〉 and the anisotropic energy flux density F(r) = 〈δu (δu)2〉, where δu is the vector velocity increment over separation r, are de ..."
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We investigate experimentally the anisotropic energy transfers in freely decaying turbulence subjected to a background rotation. The energy distribution E(r, t) = 〈(δu)2 〉 and the anisotropic energy flux density F(r) = 〈δu (δu)2〉, where δu is the vector velocity increment over separation r, are determined from large data sets of Particle Image Velocimetry measurements. Surprisingly, although E(r) is strongly anisotropic at all scales, F(r) remains almost radial, except in the neardissipative range. The anisotropy growth of decaying rotating turbulence is therefore proved to be essentially driven by a nearly radial, but orientationdependent, energy flux density F(r). 1.
Structure and Dynamics of Rotating Turbulence: A Review of Recent Experimental and Numerical Results
"... Rotating turbulence is a fundamental phenomenon appearing in several geophysical and industrial applications. Its study benefited from major advances in the recent years, but also raised new questions. We review recent results for rotating turbulence, from several numerical and experimental research ..."
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Rotating turbulence is a fundamental phenomenon appearing in several geophysical and industrial applications. Its study benefited from major advances in the recent years, but also raised new questions. We review recent results for rotating turbulence, from several numerical and experimental researches, and in relation with theory and models, mostly for homogeneous flows. We observe a convergence in the statistical description of rotating turbulence from the advent of modern experimental techniques and computational power that allows to investigate the structure and dynamics of rotating flows at similar parameters and with similar description levels. The improved picture about the anisotropization mechanisms, however, reveals subtle differences in the flow conditions, including its generation and boundary conditions, which lead to separate points of view about the role of linear mechanisms—the Coriolis force and inertial waves—compared with more complex nonlinear triadic interactions. This is discussed in relation with the most recent diagnostic of dynamical equations in physical and spectral space. [DOI: 10.1115/1.4029006] 1
INSTABILITIES AND TRANSITION IN THREEDIMENSIONAL FLOWS WITH ROTATION EXCITATION OF INERTIAL MODES IN A CLOSED GRID TURBULENCE EXPERIMENT UNDER ROTATION
"... Translating a grid in a closed volume of fluid is a convenient way to generate an approximately homogeneous and isotropic turbulence when a compact system is needed, e.g. when experiments are performed in a rotating frame [1, 2, 3, 4]. Such flow excited by a grid translation is, in general, composed ..."
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Translating a grid in a closed volume of fluid is a convenient way to generate an approximately homogeneous and isotropic turbulence when a compact system is needed, e.g. when experiments are performed in a rotating frame [1, 2, 3, 4]. Such flow excited by a grid translation is, in general, composed of a superposition of (i) a reproducible flow (determined through ensemble averaging) and (ii) a nonreproducible turbulent flow. In the presence of background rotation, both of these two flow components may excite inertial waves [5], which propagate because of the restoring nature of the Coriolis force. The excited inertial waves are respectively (i) reproducible —and therefore detectable in the ensemble average— and (ii) nonreproducible —detectable in the individual realizations only — [6]. In a closed container, inertial waves may appear in the form of standing inertial modes, which are the eigenmodes of the container geometry [7, 8]. Excitation of inertial modes in gridgenerated turbulence has been first observed by Dalziel [1] and are also visible in the experiments of Morize and Moisy [9] and Moisy et al. [10]. They have been characterized by Bewley et al. [3], who found good agreement between the measured frequencies and the numerical results of Maas [8]. We investigate here the structure of these inertial modes and we explore to what extent they may be reduced [6]. A square water tank is mounted on a rotating platform, and velocity fields in a vertical plane are measured using a corotating Particle Image Velocimetry system. Two grid configurations have been used: a “simple ” grid, of mesh size 40 mm, and a “modified ” grid, on the top of which a set of inner sidewalls is attached. We demonstrate that, in the latter configuration,
asymmetry in decaying rotating turbulence
, 2010
"... Decay laws, anisotropy and cyclone–anticyclone ..."
Rotating Taylor–Green flow
, 2015
"... The steady state of a forced Taylor–Green flow is investigated in a rotating frame of reference. The investigation involves the results of 184 numerical simulations for different Reynolds numbers ReF and Rossby numbers RoF. The large number of examined runs allows a systematic study that enables the ..."
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The steady state of a forced Taylor–Green flow is investigated in a rotating frame of reference. The investigation involves the results of 184 numerical simulations for different Reynolds numbers ReF and Rossby numbers RoF. The large number of examined runs allows a systematic study that enables the mapping of the different behaviours observed to the parameter space (ReF, RoF), and the examination of different limiting procedures for approaching the large ReF small RoF limit. Four distinctly different states were identified: laminar, intermittent bursts, quasitwodimensional condensates and weakly rotating turbulence. These four different states are separated by powerlaw boundaries RoF ∝ Re−γF in the small RoF limit. In this limit, the predictions of asymptotic expansions can be directly compared with the results of the direct numerical simulations. While the firstorder expansion is in good agreement with the results of the linear stability theory, it fails to reproduce the dynamical behaviour of the quasitwodimensional part of the flow in the nonlinear regime, indicating that higherorder terms in the expansion need to be taken into account. The large number of simulations allows also to investigate the scaling that relates the amplitude of the fluctuations with the energy dissipation rate and the control parameters of the system for the different states of the flow. Different scaling was observed for different states of the flow, that are discussed in detail. The present results clearly demonstrate that the limits of small Rossby and large Reynolds numbers do not commute and it is important to specify the order in which they are taken. Key words: rotating flows, rotating turbulence 1.
unknown title
, 2014
"... The steady state of a forced TaylorGreen flow is investigated in a rotating frame of reference. The investigation involves the results of 184 numerical simulations for different ..."
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The steady state of a forced TaylorGreen flow is investigated in a rotating frame of reference. The investigation involves the results of 184 numerical simulations for different
ABSTRACT Title of dissertation: TURBULENT SHEAR FLOW IN A RAPIDLY ROTATING SPHERICAL ANNULUS
"... This dissertation presents experimental measurements of torque, wall shear stress, pressure, and velocity in the boundarydriven turbulent flow of water between concentric, independently rotating spheres, commonly known as spherical Couette flow. The spheres ’ radius ratio is 0.35, geometrically sim ..."
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This dissertation presents experimental measurements of torque, wall shear stress, pressure, and velocity in the boundarydriven turbulent flow of water between concentric, independently rotating spheres, commonly known as spherical Couette flow. The spheres ’ radius ratio is 0.35, geometrically similar to that of Earth’s core. The measurements are performed at unprecedented Reynolds number for this geometry, as high as fiftysix million. The role of rapid overall rotation on the turbulence is investigated. A number of different turbulent flow states are possible, selected by the Rossby number, a dimensionless measure of the differential rotation. In certain ranges of the Rossby number near state borders, bistable coexistence of states is possible. In these ranges the flow undergoes intermittent transitions between neighboring states. At fixed Rossby number, the flow properties vary with Reynolds number in a way similar to that of other turbulent flows. At most parameters investigated, the large scales of the turbulent flow are characterized by systemwide spatial and temporal correlations that coexist with intense broadband velocity fluctuations. Some of these wavelike motions are iden