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Hao, Keli, Koji Nagata et Yi Zhou. « Scale-by-scale energy transfer in a dual-plane jet flow ». Physics of Fluids 32, no 10 (1 octobre 2020) : 105107. http://dx.doi.org/10.1063/5.0022103.
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Togni, Riccardo, Andrea Cimarelli et Elisabetta De Angelis. « Physical and scale-by-scale analysis of Rayleigh–Bénard convection ». Journal of Fluid Mechanics 782 (8 octobre 2015) : 380–404. http://dx.doi.org/10.1017/jfm.2015.547.
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A novel approach for the study of turbulent Rayleigh–Bénard convection (RBC) in the compound physical/scale space domain is presented. All data come from direct numerical simulations of turbulent RBC in a laterally unbounded domain confined between two horizontal walls, for Prandtl number $0.7$ and Rayleigh numbers $1.7\times 10^{5}$, $1.0\times 10^{6}$ and $1.0\times 10^{7}$. A preliminary analysis of the flow topology focuses on the events of impingement and emission of thermal plumes, which are identified here in terms of the horizontal divergence of the instantaneous velocity field. The flow dynamics is then described in more detail in terms of turbulent kinetic energy and temperature variance budgets. Three distinct regions where turbulent fluctuations are produced, transferred and finally dissipated are identified: a bulk region, a transitional layer and a boundary layer. A description of turbulent RBC dynamics in both physical and scale space is finally presented, completing the classic single-point balances. Detailed scale-by-scale budgets for the second-order velocity and temperature structure functions are shown for different geometrical locations. An unexpected behaviour is observed in both the viscous and thermal transitional layers consisting of a diffusive reverse transfer from small to large scales of velocity and temperature fluctuations. Through the analysis of the instantaneous field in terms of the horizontal divergence, it is found that the enlargement of thermal plumes following the impingement represents the triggering mechanism which entails the reverse transfer. The coupling of this reverse transfer with the spatial transport towards the wall is an interesting mechanism found at the basis of some peculiar aspects of the flow. As an example, it is found that, during the impingement, the presence of the wall is felt by the plumes through the pressure field mainly at large scales. These and other peculiar aspects shed light on the role of thermal plumes in the self-sustained cycle of turbulence in RBC, and may have strong repercussions on both theoretical and modelling approaches to convective turbulence.
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Ngan, K., P. Bartello et D. N. Straub. « Dissipation of Synoptic-Scale Flow by Small-Scale Turbulence ». Journal of the Atmospheric Sciences 65, no 3 (1 mars 2008) : 766–91. http://dx.doi.org/10.1175/2007jas2265.1.
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Abstract Although it is now accepted that imbalance in the atmosphere and ocean is generic, the feedback of the unbalanced motion on the balanced flow has not received much attention. In this work the parameterization problem is examined in the context of rotating stratified turbulence, that is, with a nonhydrostatic Boussinesq model. Using the normal modes as a first approximation to the balanced and unbalanced flow, the growth of ageostrophic perturbations to the quasigeostrophic flow and the associated feedback are studied. For weak stratification, there are analogies with the three-dimensionalization of decaying 2D turbulence: the growth rate of the ageostrophic perturbation follows a linear estimate, geostrophic energy is extracted from the base flow, and the associated damping on the geostrophic base flow (the “eddy viscosity”) is peaked at large horizontal scales. For strong stratification, the transfer spectra and eddy viscosities maintain this structure if there is synoptic-scale motion and the buoyancy scale is adequately resolved. This has been confirmed for global Rossby and Froude numbers of O(0.1). Implications for atmospheric and oceanic modeling are discussed.
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Bengtsson, Lisa, Heiner Körnich, Erland Källén et Gunilla Svensson. « Large-Scale Dynamical Response to Subgrid-Scale Organization Provided by Cellular Automata ». Journal of the Atmospheric Sciences 68, no 12 (1 décembre 2011) : 3132–44. http://dx.doi.org/10.1175/jas-d-10-05028.1.
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Abstract Because of the limited resolution of numerical weather prediction (NWP) models, subgrid-scale physical processes are parameterized and represented by gridbox means. However, some physical processes are better represented by a mean and its variance; a typical example is deep convection, with scales varying from individual updrafts to organized mesoscale systems. This study investigates, in an idealized setting, whether a cellular automaton (CA) can be used to enhance subgrid-scale organization by forming clusters representative of the convective scales and thus yield a stochastic representation of subgrid-scale variability. The authors study the transfer of energy from the convective to the larger atmospheric scales through nonlinear wave interactions. This is done using a shallow water (SW) model initialized with equatorial wave modes. By letting a CA act on a finer resolution than that of the SW model, it can be expected to mimic the effect of, for instance, gravity wave propagation on convective organization. Employing the CA scheme permits the reproduction of the observed behavior of slowing down equatorial Kelvin modes in convectively active regions, while random perturbations fail to feed back on the large-scale flow. The analysis of kinetic energy spectra demonstrates that the CA subgrid scheme introduces energy backscatter from the smallest model scales to medium scales. However, the amount of energy backscattered depends almost solely on the memory time scale introduced to the subgrid scheme, whereas any variation in spatial scales generated does not influence the energy spectra markedly.
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MIYAUCHI, Toshio, Mamoru TANAHASHI et Takashi KAKUWA. « Evaluation of Energy Transfer between Grid Scale and Subgrid Scale by Direct Numerical Simulation Data Base. » Transactions of the Japan Society of Mechanical Engineers Series B 62, no 596 (1996) : 1406–13. http://dx.doi.org/10.1299/kikaib.62.1406.
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Touber, Emile. « Small-scale two-dimensional turbulence shaped by bulk viscosity ». Journal of Fluid Mechanics 875 (26 juillet 2019) : 974–1003. http://dx.doi.org/10.1017/jfm.2019.531.
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Bulk-to-shear viscosity ratios of three orders of magnitude are often reported in carbon dioxide but are always neglected when predicting aerothermal loads in external (Mars exploration) or internal (turbomachinery, heat exchanger) turbulent flows. The recent (and first) numerical investigations of that matter suggest that the solenoidal turbulence kinetic energy is in fact well predicted despite this seemingly arbitrary simplification. The present work argues that such a conclusion may reflect limitations from the choice of configuration rather than provide a definite statement on the robustness of kinetic-energy transfers to the use of Stokes’ hypothesis. Two distinct asymptotic regimes (Euler–Landau and Stokes–Newton) in the eigenmodes of the Navier–Stokes equations are identified. In the Euler–Landau regime, the one captured by earlier studies, acoustic and entropy waves are damped by transport coefficients and the dilatational kinetic energy is dissipated, even more rapidly for high bulk-viscosity fluids and/or forcing frequencies. If the kinetic energy is initially or constantly injected through solenoidal motions, effects on the turbulence kinetic energy remain minor. However, in the Stokes–Newton regime, diffused bulk compressions and advected isothermal compressions are found to prevail and promote small-scale enstrophy via vorticity–dilatation correlations. In the absence of bulk viscosity, the transition to the Stokes–Newton regime occurs within the dissipative scales and is not observed in practice. In contrast, at high bulk viscosities, the Stokes–Newton regime can be made to overlap with the inertial range and disrupt the enstrophy at small scales, which is then dissipated by friction. Thus, flows with substantial inertial ranges and large bulk-to-shear viscosity ratios should experience enhanced transfers to small-scale solenoidal kinetic energy, and therefore faster dissipation rates leading to modifications of the heat-transfer properties. Observing numerically such transfers is still prohibitively expensive, and the present simulations are restricted to two-dimensional turbulence. However, the theory laid here offers useful guidelines to design experimental studies to track the Stokes–Newton regime and associated modifications of the turbulence kinetic energy, which are expected to persist in three-dimensional turbulence.
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Agudelo Rueda, Jeffersson A., Daniel Verscharen, Robert T. Wicks, Christopher J. Owen, Georgios Nicolaou, Kai Germaschewski, Andrew P. Walsh, Ioannis Zouganelis et Santiago Vargas Domínguez. « Energy Transport during 3D Small-scale Reconnection Driven by Anisotropic Plasma Turbulence ». Astrophysical Journal 938, no 1 (1 octobre 2022) : 4. http://dx.doi.org/10.3847/1538-4357/ac8667.
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Abstract Energy dissipation in collisionless plasmas is a long-standing fundamental physics problem. Although it is well known that magnetic reconnection and turbulence are coupled and transport energy from system-size scales to subproton scales, the details of the energy distribution and energy dissipation channels remain poorly understood. Especially, the energy transfer and transport associated with 3D small-scale reconnection that occurs as a consequence of a turbulent cascade is unknown. We use an explicit fully kinetic particle-in-cell code to simulate 3D small-scale magnetic reconnection events forming in anisotropic and decaying Alfvénic turbulence. We identify a highly dynamic and asymmetric reconnection event that involves two reconnecting flux ropes. We use a two-fluid approach based on the Boltzmann equation to study the spatial energy transfer associated with the reconnection event and compare the power density terms in the two-fluid energy equations with standard energy-based damping, heating, and dissipation proxies. Our findings suggest that the electron bulk flow transports thermal energy density more efficiently than kinetic energy density. Moreover, in our turbulent reconnection event, the energy density transfer is dominated by plasma compression. This is consistent with turbulent current sheets and turbulent reconnection events, but not with laminar reconnection.
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MIYAUCHI, Toshio, Mamoru TANAHASHI et Takashi KAKUWA. « Evaluation of Energy Transfer between Grid Scale and Subgrid Scale by Use of Direct Numerical Simulation Data Base. » JSME International Journal Series B 40, no 3 (1997) : 343–50. http://dx.doi.org/10.1299/jsmeb.40.343.
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Cortese, Barbara, Claudia Piliego, Ilenia Viola, Stefania D’Amone, Roberto Cingolani et Giuseppe Gigli. « Engineering Transfer of Micro- and Nanometer-Scale Features by Surface Energy Modification ». Langmuir 25, no 12 (16 juin 2009) : 7025–31. http://dx.doi.org/10.1021/la900248j.
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Aluie, Hussein, Matthew Hecht et Geoffrey K. Vallis. « Mapping the Energy Cascade in the North Atlantic Ocean : The Coarse-Graining Approach ». Journal of Physical Oceanography 48, no 2 (février 2018) : 225–44. http://dx.doi.org/10.1175/jpo-d-17-0100.1.
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AbstractA coarse-graining framework is implemented to analyze nonlinear processes, measure energy transfer rates, and map out the energy pathways from simulated global ocean data. Traditional tools to measure the energy cascade from turbulence theory, such as spectral flux or spectral transfer, rely on the assumption of statistical homogeneity or at least a large separation between the scales of motion and the scales of statistical inhomogeneity. The coarse-graining framework allows for probing the fully nonlinear dynamics simultaneously in scale and in space and is not restricted by those assumptions. This paper describes how the framework can be applied to ocean flows. Energy transfer between scales is not unique because of a gauge freedom. Here, it is argued that a Galilean-invariant subfilter-scale (SFS) flux is a suitable quantity to properly measure energy scale transfer in the ocean. It is shown that the SFS definition can yield answers that are qualitatively different from traditional measures that conflate spatial transport with the scale transfer of energy. The paper presents geographic maps of the energy scale transfer that are both local in space and allow quasi-spectral, or scale-by-scale, dynamics to be diagnosed. Utilizing a strongly eddying simulation of flow in the North Atlantic Ocean, it is found that an upscale energy transfer does not hold everywhere. Indeed certain regions near the Gulf Stream and in the Equatorial Countercurrent have a marked downscale transfer. Nevertheless, on average an upscale transfer is a reasonable mean description of the extratropical energy scale transfer over regions of O(103) km in size.
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Brunner-Suzuki, Anne-Marie E. G., Miles A. Sundermeyer et M. Pascale Lelong. « Upscale Energy Transfer by the Vortical Mode and Internal Waves ». Journal of Physical Oceanography 44, no 9 (1 septembre 2014) : 2446–69. http://dx.doi.org/10.1175/jpo-d-12-0149.1.
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Abstract Diapycnal mixing in the ocean is sporadic yet ubiquitous, leading to patches of mixing on a variety of scales. The adjustment of such mixed patches can lead to the formation of vortices and other small-scale geostrophic motions, which are thought to enhance lateral diffusivity. If vortices are densely populated, they can interact and merge, and upscale energy transfer can occur. Vortex interaction can also be modified by internal waves, thus impacting upscale transfer. Numerical experiments were used to study the effect of a large-scale near-inertial internal wave on a field of submesoscale vortices. While one might expect a vertical shear to limit the vertical scale of merging vortices, it was found that internal wave shear did not disrupt upscale energy transfer. Rather, under certain conditions, it enhanced upscale transfer by enhancing vortex–vortex interaction. If vortices were so densely populated that they interacted even in the absence of a wave, adding a forced large-scale wave enhanced the existing upscale transfer. Results further suggest that continuous forcing by the main driving mechanism (either vortices or internal waves) is necessary to maintain such upscale transfer. These findings could help to improve understanding of the direction of energy transfer in submesoscale oceanic processes.
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San Liang, X. « Canonical Transfer and Multiscale Energetics for Primitive and Quasigeostrophic Atmospheres ». Journal of the Atmospheric Sciences 73, no 11 (24 octobre 2016) : 4439–68. http://dx.doi.org/10.1175/jas-d-16-0131.1.
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Abstract The past years have seen the success of a novel and rigorous localized multiscale energetics formalism in a variety of ocean and engineering fluid applications. In a self-contained way, this study introduces it to the atmospheric dynamical diagnostics, with important theoretical updates and clarifications of some common misconceptions about multiscale energy. Multiscale equations are derived using a new analysis apparatus—namely, multiscale window transform—with respect to both the primitive equation and quasigeostrophic models. A reconstruction of the “atomic” energy fluxes on the multiple scale windows allows for a natural and unique separation of the in-scale transports and cross-scale transfers from the intertwined nonlinear processes. The resulting energy transfers bear a Lie bracket form, reminiscent of the Poisson bracket in Hamiltonian mechanics; hence, we would call them “canonical.” A canonical transfer process is a mere redistribution of energy among scale windows, without generating or destroying energy as a whole. By classification, a multiscale energetic cycle comprises available potential energy (APE) transport, kinetic energy (KE) transport, pressure work, buoyancy conversion, work done by external forcing and friction, and the cross-scale canonical transfers of APE and KE, which correspond respectively to the baroclinic and barotropic instabilities in geophysical fluid dynamics. A buoyancy conversion takes place in an individual window only, bridging the two types of energy, namely, KE and APE; it does not involve any processes among different scale windows and is hence basically not related to instabilities. This formalism is exemplified with a preliminary application to the study of the Madden–Julian oscillation.
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Carter, Douglas W., et Filippo Coletti. « Small-scale structure and energy transfer in homogeneous turbulence ». Journal of Fluid Mechanics 854 (12 septembre 2018) : 505–43. http://dx.doi.org/10.1017/jfm.2018.616.
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We use high-resolution velocity measurements in a jet-stirred zero-mean-flow facility to investigate the topology and energy transfer properties of homogeneous turbulence over the Reynolds number range $Re_{\unicode[STIX]{x1D706}}\approx 300$–500. The probability distributions of the enstrophy and strain-rate fields show long tails associated with the most intense events, while the weaker events behave as random variables. The high-enstrophy and high-strain structures are shaped as tube-like and sheet-like objects, respectively, the latter often wrapped around the former. Both types of structures have thickness that scales in Kolmogorov units, and display self-similar topology over a wide range of scales. The small-scale turbulence activity is found to be strongly correlated with the large-scale activity, suggesting that the phenomenon of amplitude modulation (previously observed in advection-dominated shear flows) is not limited to specific production mechanisms. Observing the significant variations in spatially averaged enstrophy, we heuristically define hyperactive and sleeping states of the flow: these also correspond to, respectively, high and low levels of large-scale velocity gradients. Moreover, the hyperactive and sleeping states contribute very differently to the inter-scale energy flux, characterized via the nonlinear transfer term in the Kármán–Howarth–Monin equation. While the energy cascades to smaller scales along the jet-axis direction, a weaker but sizable inverse transfer is observed along the transverse direction; a behaviour so far only observed in spatially developing flows. The hyperactive states are characterized by very intense energy transfers, while the sleeping states account for weaker fluxes, largely directed from small to large scales. This implies that the form of energy cascade depends on the presence (or absence) of intense turbulent structures. These results are at odds with the classic concept of the energy cascade between adjacent scales, but are compatible with the view of a cascade in physical space.
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Kim, J., M. Bassenne, C. A. Z. Towery, P. E. Hamlington, A. Y. Poludnenko et J. Urzay. « Spatially localized multi-scale energy transfer in turbulent premixed combustion ». Journal of Fluid Mechanics 848 (4 juin 2018) : 78–116. http://dx.doi.org/10.1017/jfm.2018.371.
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A three-dimensional wavelet multi-resolution analysis of direct numerical simulations of a turbulent premixed flame is performed in order to investigate the spatially localized spectral transfer of kinetic energy across scales in the vicinity of the flame front. A formulation is developed that addresses the compressible spectral dynamics of the kinetic energy in wavelet space. The wavelet basis enables the examination of local energy spectra, along with inter-scale and subfilter-scale (SFS) cumulative energy fluxes across a scale cutoff, all quantities being available either unconditioned or conditioned on the local instantaneous value of the progress variable across the flame brush. The results include the quantification of mean spectral values and associated spatial variabilities. The energy spectra undergo, in most locations in the flame brush, a precipitous drop that starts at scales of the same order as the characteristic flame scale and continues to smaller scales, even though the corresponding decrease of the mean spectra is much more gradual. The mean convective inter-scale flux indicates that convection increases the energy of small scales, although it does so in a non-conservative manner due to the high aspect ratio of the grid, which limits the maximum scale level that can be used in the wavelet transform, and to the non-periodic boundary conditions, which exchange energy through surface forces, as explicitly elucidated by the formulation. The mean pressure-gradient inter-scale flux extracts energy from intermediate scales of the same order as the characteristic flame scale, and injects energy in the smaller and larger scales. The local SFS-cumulative contribution of the convective and pressure-gradient mechanisms of energy transfer across a given cutoff scale imposed by a wavelet filter is analysed. The local SFS-cumulative energy flux is such that the subfilter scales upstream from the flame always receive energy on average. Conversely, within the flame brush, energy is drained on average from the subfilter scales by convective and pressure-gradient effects most intensely when the filter cutoff is larger than the characteristic flame scale.
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Bendix, P. M., M. S. Pedersen et D. Stamou. « Quantification of nano-scale intermembrane contact areas by using fluorescence resonance energy transfer ». Proceedings of the National Academy of Sciences 106, no 30 (13 juillet 2009) : 12341–46. http://dx.doi.org/10.1073/pnas.0903052106.
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Hablot, Delphine, Raymond Ziessel, Mohammed A. H. Alamiry, Effat Bahraidah et Anthony Harriman. « Nanomechanical properties of molecular-scale bridges as visualised by intramolecular electronic energy transfer ». Chem. Sci. 4, no 1 (2013) : 444–53. http://dx.doi.org/10.1039/c2sc21505e.
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Nicholls, Melville E., et Roger A. Pielke Sr. « On the role of thermal expansion and compression in large-scale atmospheric energy and mass transports ». Atmospheric Chemistry and Physics 18, no 21 (7 novembre 2018) : 15975–6003. http://dx.doi.org/10.5194/acp-18-15975-2018.
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Abstract. There are currently two views of how atmospheric total energy transport is accomplished. The traditional view considers total energy as a quantity that is transported in an advective-like manner by the wind. The other considers that thermal expansion and the resultant compression of the surrounding air causes a transport of total energy in a wave-like manner at the speed of sound. This latter view emerged as the result of detailed analysis of fully compressible mesoscale model simulations that demonstrated considerable transfer of internal and gravitational potential energy at the speed of sound by Lamb waves. In this study, results are presented of idealized experiments with a fully compressible model designed to examine the large-scale transfers of total energy and mass when local heat sources are prescribed. For simplicity a Cartesian grid was used, there was a horizontally homogeneous and motionless initial state, and the simulations did not include moisture. Three main experimental designs were employed. The first has a convective-storm-scale heat source and does not include the Coriolis force. The second experiment has a continent-scale heat source prescribed near the surface to represent surface heating and includes a constant Coriolis parameter. The third experiment has a cloud-cluster-scale heat source prescribed at the equator and includes a latitude-dependent Coriolis parameter. Results show considerable amounts of meridional total energy and mass transfer at the speed of sound. This suggests that the current theory of large-scale total energy transport is incomplete. It is noteworthy that comparison of simulations with and without thermally generated compression waves show that for a very large-scale heat source there are fairly small but nevertheless significant differences of the wind field. These results raise important questions related to the mass constraints when calculating meridional energy transports, the use of semi-implicit time differencing in large-scale global models, and the use of the term “heat transfer” for total energy transfer.
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Devaux, André, et Gion Calzaferri. « Manipulation of Energy Transfer Processes in Nanochannels ». International Journal of Photoenergy 2009 (2009) : 1–9. http://dx.doi.org/10.1155/2009/741834.
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The realisation of molecular assemblies featuring specific macroscopic properties is a prime example for the versatility of supramolecular organisation. Microporous materials such as zeolite L are well suited for the preparation of host-guest composites containing dyes, complexes, or clusters. This short tutorial focuses on the possibilities offered by zeolite L to study and influence Förster resonance energy transfer inside of its nanochannels. The highly organised host-guest materials can in turn be structured on a larger scale to form macroscopic patterns, making it possible to create large-scale structures from small, highly organised building blocks for novel optical applications.
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Coburn et Sorriso-Valvo. « Energy Transfer in Incompressible Magnetohydrodynamics : The Filtered Approach ». Fluids 4, no 3 (2 septembre 2019) : 163. http://dx.doi.org/10.3390/fluids4030163.
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We develop incompressible magnetohydrodynamic (IMHD) energy budget equations witha spatial filtering kernel and estimate the scaling of the structure functions. The Politano-Pouquetlaw is recovered as an upper bound on the scale-to-scale energy transfer. The primary result ofthis work is the relation of the scaling of IMHD invariants. It can be produced by hypothesizing ascale-independent energy transfer rate. These results have relevance in plasma regimes where theapproximations of IMHD are justified. We measure structure functions with solar wind data and findsupport for the relations.
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Roy, S., R. Bandyopadhyay, Y. Yang, T. N. Parashar, W. H. Matthaeus, S. Adhikari, V. Roytershteyn et al. « Turbulent Energy Transfer and Proton–Electron Heating in Collisionless Plasmas ». Astrophysical Journal 941, no 2 (1 décembre 2022) : 137. http://dx.doi.org/10.3847/1538-4357/aca479.
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Abstract Despite decades of study of high-temperature weakly collisional plasmas, a complete understanding of how energy is transferred between particles and fields in turbulent plasmas remains elusive. Two major questions in this regard are how fluid-scale energy transfer rates, associated with turbulence, connect with kinetic-scale dissipation, and what controls the fraction of dissipation on different charged species. Although the rate of cascade has long been recognized as a limiting factor in the heating rate at kinetic scales, there has not been direct evidence correlating the heating rate with MHD-scale cascade rates. Using kinetic simulations and in situ spacecraft data, we show that the fluid-scale energy flux indeed accounts for the total energy dissipated at kinetic scales. A phenomenology, based on disruption of proton gyromotion by fluctuating electric fields that are produced in turbulence at proton scales, argues that the proton versus electron heating is controlled by the ratio of the nonlinear timescale to the proton cyclotron time and by the plasma beta. The proposed scalings are supported by the simulations and observations.
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Harper, Katie L., Sergey V. Nazarenko, Sergey B. Medvedev et Colm Connaughton. « Wave turbulence in the two-layer ocean model ». Journal of Fluid Mechanics 756 (1 septembre 2014) : 309–27. http://dx.doi.org/10.1017/jfm.2014.465.
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AbstractThis paper looks at the two-layer ocean model from a wave-turbulence (WT) perspective. A symmetric form of the two-layer kinetic equation for Rossby waves is derived using canonical variables, allowing the turbulent cascade of energy between the barotropic and baroclinic modes to be studied. It is already well known that in two-layers, energy is transferred via triad interactions from the large-scale baroclinic modes to the baroclinic and barotropic modes at the Rossby deformation scale, where barotropization takes place, and from there to the large-scale barotropic modes via an inverse transfer. However, by applying WT theory, we find that energy is transferred via dominant $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\{+--\}$ triads with one barotropic component and two baroclinic components, and that the direct transfer of energy is local and the inverse energy transfer is non-local. We study this non-locality using scale separation and obtain a system of coupled equations for the small-scale baroclinic component and the large-scale barotropic component. Since the total energy of the small-scale component is not conserved, but the total barotropic plus baroclinic energy is conserved, the baroclinic energy loss at small scales will be compensated by the growth of the barotropic energy at large scales. Using the frequency resonance condition, we show that in the presence of the beta-effect this transfer is mostly anisotropic and mostly to the zonal component.
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Eghdami, Masih, Shanti Bhushan et Ana P. Barros. « Direct Numerical Simulations to Investigate Energy Transfer between Meso- and Synoptic Scales ». Journal of the Atmospheric Sciences 75, no 4 (1 avril 2018) : 1163–71. http://dx.doi.org/10.1175/jas-d-17-0216.1.
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Abstract Understanding the development of the atmospheric energy spectrum across scales is necessary to elucidate atmospheric predictability. In this manuscript, the authors investigate energy transfer between the synoptic scale and the mesoscale using direct numerical simulations (DNSs) of two-dimensional (2D) turbulence transfer under forcing applied at different scales. First, DNS results forced by a single kinetic energy source at large scales show that the energy spectra slopes of the direct enstrophy cascade are steeper than the theoretically predicted −3 slope. Second, the presence of two inertial ranges in 2D turbulence at intermediate scales is investigated by introducing a second energy source in the meso-α-scale range. The energy spectra for the DNS with two kinetic energy sources exhibit flatter slopes that are closer to −3, consistent with the observed kinetic energy spectra of horizontal winds in the atmosphere at synoptic scales. Further, the results are independent of model resolution and scale separation between the two energy sources, with a robust transition region between the lower synoptic and the upper meso-α scales in agreement with classical observations in the upper troposphere. These results suggest the existence of a mesoscale feedback on synoptic-scale predictability that emerges from the concurrence of the direct (downscale) enstrophy transfer in the synoptic scales and the inverse (upscale) kinetic energy transfer from the mesoscale to the synoptic scale in the troposphere.
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Cho, Minjeong, Yongyun Hwang et Haecheon Choi. « Scale interactions and spectral energy transfer in turbulent channel flow ». Journal of Fluid Mechanics 854 (10 septembre 2018) : 474–504. http://dx.doi.org/10.1017/jfm.2018.643.
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Spectral energy transfer in a turbulent channel flow is investigated at Reynolds number $Re_{\unicode[STIX]{x1D70F}}\simeq 1700$, based on the wall shear velocity and channel half-height, with a particular emphasis on full visualization of triadic wave interactions involved in turbulent transport. As in previous studies, turbulent production is found to be almost uniform, especially over the logarithmic region, and the related spanwise integral length scale is approximately proportional to the distance from the wall. In the logarithmic and outer regions, the energy balance at the integral length scales is mainly formed between production and nonlinear turbulent transport, the latter of which plays the central role in the energy cascade down to the Kolmogorov microscale. While confirming the classical role of the turbulent transport, the triadic wave interaction analysis unveils two new types of scale interaction processes, highly active in the near-wall and the lower logarithmic regions. First, for relatively small energy-containing motions, part of the energy transfer mechanisms from the integral to the adjacent small length scale in the energy cascade is found to be provided by the interactions between larger energy-containing motions. It is subsequently shown that this is related to involvement of large energy-containing motions in skin-friction generation. Second, there exists a non-negligible amount of energy transfer from small to large integral scales in the process of downward energy transfer to the near-wall region. This type of scale interaction is predominant only for the streamwise and spanwise velocity components, and it plays a central role in the formation of the wall-reaching inactive part of large energy-containing motions. A further analysis reveals that this type of scale interaction leads the wall-reaching inactive part to scale in the inner units, consistent with the recent observation. Finally, it is proposed that turbulence production and pressure–strain spectra support the existence of the self-sustaining process as the main turnover dynamics of all the energy-containing motions.
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Rai, Shikhar, Matthew Hecht, Matthew Maltrud et Hussein Aluie. « Scale of oceanic eddy killing by wind from global satellite observations ». Science Advances 7, no 28 (juillet 2021) : eabf4920. http://dx.doi.org/10.1126/sciadv.abf4920.
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Wind is the primary driver of the oceanic general circulation, yet the length scales at which this energy transfer occurs are unknown. Using satellite data and a recent method to disentangle multiscale processes, we find that wind deposits kinetic energy into the geostrophic ocean flow only at scales larger than 260 km, on a global average. We show that wind removes energy from scales smaller than 260 km at an average rate of −50 GW, a process known as eddy killing. To our knowledge, this is the first objective determination of the global eddy killing scale. We find that eddy killing is taking place at almost all times but with seasonal variability, peaking in winter, and it removes a substantial fraction (up to 90%) of the wind power input in western boundary currents. This process, often overlooked in analyses and models, is a major dissipation pathway for mesoscales, the ocean’s most energetic scales.
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Vakakis, Alexander F. « Passive nonlinear targeted energy transfer ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 376, no 2127 (23 juillet 2018) : 20170132. http://dx.doi.org/10.1098/rsta.2017.0132.
Texte intégralRésumé :
Nonlinearity in dynamics and acoustics may be viewed as scattering of energy across frequencies/wavenumbers. This is in contrast with linear systems when no such scattering exists. Motivated by irreversible large-to-small-scale energy transfers in turbulent flows, passive targeted energy transfers (TET) in mechanical and structural systems incorporating intentional strong nonlinearities are considered. Transient or permanent resonance captures are basic mechanisms for inducing TET in such systems, as well as nonlinear energy scattering across scales caused by strongly nonlinear resonance interactions. Certain theoretical concepts are reviewed, and some TET applications are discussed. Specifically, it is shown that the addition of strongly nonlinear local attachments in an otherwise linear dynamical system may induce energy scattering across scales and ‘redistribution' of input energy from large to small scales in the linear modal space, in similarity to energy cascades that occur in turbulent flows. Such effects may be intentionally induced in the design stage and may lead to improved performance, e.g. it terms of vibration and shock isolation or energy harvesting. In addition, a simple mechanical analogue in the form of a nonlinear planar chain of particles composed of linear stiffness elements but exhibiting strong nonlinearity due to kinematic and geometric effects is discussed, exhibiting similar energy scattering across scales in its acoustics. These results demonstrate the efficacy of intentional utilization of strong nonlinearity in design to induce predictable and controlled intense multi-scale energy transfers in the dynamics and acoustics of a broad class of systems and structures, thus achieving performance objectives that would be not possible in classical linear settings. This article is part of the theme issue ‘Nonlinear energy transfer in dynamical and acoustical systems’.
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CASCIOLA, C. M., et E. DE ANGELIS. « Energy transfer in turbulent polymer solutions ». Journal of Fluid Mechanics 581 (22 mai 2007) : 419–36. http://dx.doi.org/10.1017/s0022112007006003.
Texte intégralRésumé :
The paper addresses a set of new equations concerning the scale-by-scale balance of turbulent fluctuations in dilute polymer solutions. The main difficulty is the energy associated with the polymers, which is not of a quadratic form in terms of the traditional descriptor of the micro-structure. A different choice is however possible, which, at least for mild stretching of the polymeric chains, directly leads to an L2 structure for the total free-energy density of the system thus allowing the extension of the classical method to polymeric fluids. On this basis, the energy budget in spectral space is discussed, providing the spectral decomposition of the energy of the system. New equations are also derived in physical space, to provide balance equations for the fluctuations in both the kinetic field and the micro-structure, thus extending, in a sense, the celebrated Kármán–Howarth and Kolmogorov equations of classical turbulence theory. The paper is limited to the context of homogeneous turbulence. However the necessary steps required to expand the treatment to wall-bounded flows of polymeric liquids are indicated in detail.
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Liao, Yang, et Nicholas T. Ouellette. « Spatial structure of spectral transport in two-dimensional flow ». Journal of Fluid Mechanics 725 (14 mai 2013) : 281–98. http://dx.doi.org/10.1017/jfm.2013.187.
Texte intégralRésumé :
AbstractUsing filter-space techniques (FSTs), we study the spatial structure of the scale-to-scale flux of energy in two-dimensional flow. Analysing data from a weakly turbulent, experimental quasi-two-dimensional flow, we find rotationally symmetric patterns consisting of lobes of spectral flux of alternating sign that are associated with vortical motion in the flow field. Such patterns also occur in a simple analytical model, even though the single-scale model flow should have no scale-to-scale energy transfer. Thus, the interpretation of these alternating patterns must be handled with care. By decomposing the spectral flux into three distinct components, we show that these lobe patterns are entirely associated with the Leonard and, to a lesser extent, cross terms. In addition, we show that the contributions from these two terms are localized around the energy injection scale, and that the bulk of the inverse energy transfer in our flow is carried by the subgrid term alone.
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Kawata, Takuya, et Takahiro Tsukahara. « Spectral Analysis on Transport Budgets of Turbulent Heat Fluxes in Plane Couette Turbulence ». Energies 15, no 14 (20 juillet 2022) : 5258. http://dx.doi.org/10.3390/en15145258.
Texte intégralRésumé :
In recent years, scale-by-scale energy transport in wall turbulence has been intensively studied, and the complex spatial and interscale transfer of turbulent energy has been investigated. As the enhancement of heat transfer is one of the most important aspects of turbulence from an engineering perspective, it is also important to study how turbulent heat fluxes are transported in space and in scale by nonlinear multi-scale interactions in wall turbulence as well as turbulent energy. In the present study, the spectral transport budgets of turbulent heat fluxes are investigated based on direct numerical simulation data of a turbulent plane Couette flow with a passive scalar heat transfer. The transport budgets of spanwise spectra of temperature fluctuation and velocity-temperature correlations are investigated in detail in comparison to those of the corresponding Reynolds stress spectra. The similarity and difference between those scale-by-scale transports are discussed, with a particular focus on the roles of interscale transport and spatial turbulent diffusion. As a result, it is found that the spectral transport of the temperature-related statistics is quite similar to those of the Reynolds stresses, and in particular, the inverse interscale transfer is commonly observed throughout the channel in both transport of the Reynolds shear stress and wall-normal turbulent heat flux.
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Wang, Jianchun, Minping Wan, Song Chen et Shiyi Chen. « Kinetic energy transfer in compressible isotropic turbulence ». Journal of Fluid Mechanics 841 (26 février 2018) : 581–613. http://dx.doi.org/10.1017/jfm.2018.23.
Texte intégralRésumé :
Kinetic energy transfer in compressible isotropic turbulence is studied using numerical simulations with solenoidal forcing at turbulent Mach numbers ranging from 0.4 to 1.0 and at a Taylor Reynolds number of approximately 250. The pressure dilatation plays an important role in the local conversion between kinetic energy and internal energy, but its net contribution to the average kinetic energy transfer is negligibly small, due to the cancellation between compression and expansion work. The right tail of probability density function (PDF) of the subgrid-scale (SGS) flux of kinetic energy is found to be longer at higher turbulent Mach numbers. With an increase of the turbulent Mach number, compression motions enhance the positive SGS flux, and expansion motions enhance the negative SGS flux. Average of SGS flux conditioned on the filtered velocity divergence is studied by numerical analysis and a heuristic model. The conditional average of SGS flux is shown to be proportional to the square of filtered velocity divergence in strong compression regions for turbulent Mach numbers from 0.6 to 1.0. Moreover, the antiparallel alignment between the large-scale strain and the SGS stress is observed in strong compression regions. The inter-scale transfer of solenoidal and compressible components of kinetic energy is investigated by Helmholtz decomposition. The SGS flux of solenoidal kinetic energy is insensitive to the change of turbulent Mach number, while the SGS flux of compressible kinetic energy increases drastically as the turbulent Mach number becomes larger. The compressible mode persistently absorbs energy from the solenoidal mode through nonlinear advection. The kinetic energy of the compressible mode is transferred from large scales to small scales through the compressible SGS flux, and is dissipated by viscosity at small scales.
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GOTO, SUSUMU. « A physical mechanism of the energy cascade in homogeneous isotropic turbulence ». Journal of Fluid Mechanics 605 (23 mai 2008) : 355–66. http://dx.doi.org/10.1017/s0022112008001511.
Texte intégralRésumé :
In order to investigate the physical mechanism of the energy cascade in homogeneous isotropic turbulence, the internal energy and its transfer rate are defined as a function of scale, space and time. Direct numerical simulation of turbulence at a moderate Reynolds number verifies that the energy cascade can be caused by the successive creation of smaller-scale tubular vortices in the larger-scale straining regions existing between pairs of larger-scale tubular vortices. Movies are available with the online version of the paper.
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Harvey, Pierre D., Christine Stern, Claude P. Gros et Roger Guilard. « Through space singlet energy transfers in light-harvesting systems and cofacial bisporphyrin dyads ». Journal of Porphyrins and Phthalocyanines 14, no 01 (janvier 2010) : 55–63. http://dx.doi.org/10.1142/s1088424610001702.
Texte intégralRésumé :
Recent discoveries from our research groups on the photophysics of a few cofacial bisporphyrin dyads for through space singlet and triplet energy transfers raised several important investigations about the mechanism of energy transfers and energy migration in light-harvesting devices, notably LH II, in the heavily investigated purple photosynthetic bacteria. The key feature is that for face-to-face and slipped dyads with controlled structure using rigid spacers or spacers with limited flexibilities, our fastest rates for singlet energy transfer are in the 10 × 109 s -1 (i.e. 100 ps time scale) for donor-acceptor distances of ~3.5–3.6 Å. The time scale for energy transfers between different bacteriochlorophylls, notably B800*→B850, is in the ps despite the long Mg ⋯ Mg separation (~18 Å). This short rate drastically contrasts with the well-accepted Förster theory. This review focuses on the photophysical processes and dynamics in LH II and compares these parameters with our investigated model dyads build upon octa-etio-porphyrin chromophores and rigid and semi-rigid spacers. The recently discovered role of the rhodopin glucoside (carotenoid) will be analyzed as possible relay for energy transfers, including the possibility of uphill processes at room temperature. In this context the concept of energy migration may be complemented by parallel relays and uphill processes. It is also becoming more obvious that the irreversible electron transfer at the reaction center (electron transfer from the special pair to the phaeophytin) renders the rates for energy transfer and migration faster precluding all possibility of back transfers.
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Barkan, Roy, Kraig B. Winters et James C. McWilliams. « Stimulated Imbalance and the Enhancement of Eddy Kinetic Energy Dissipation by Internal Waves ». Journal of Physical Oceanography 47, no 1 (janvier 2017) : 181–98. http://dx.doi.org/10.1175/jpo-d-16-0117.1.
Texte intégralRésumé :
AbstractThe effects of internal waves (IWs), externally forced by high-frequency wind, on energy pathways are studied in submesoscale-resolving numerical simulations of an idealized wind-driven channel flow. Two processes are examined: the direct extraction of mesoscale energy by externally forced IWs followed by an IW forward energy cascade to dissipation and stimulated imbalance, a mechanism through which externally forced IWs trigger a forward mesoscale to submesoscale energy cascade to dissipation. This study finds that the frequency and wavenumber spectral slopes are shallower in solutions with high-frequency forcing compared to solutions without and that the volume-averaged interior kinetic energy dissipation rate increases tenfold. The ratio between the enhanced dissipation rate and the added high-frequency wind work is 1.3, demonstrating the significance of the IW-mediated forward cascades. Temporal-scale analysis of energy exchanges among low- (mesoscale), intermediate- (submesoscale), and high-frequency (IW) bands shows a corresponding increase in kinetic energy Ek and available potential energy APE transfers from mesoscales to submesoscales (stimulated imbalance) and mesoscales to IWs (direct extraction). Two direct extraction routes are identified: a mesoscale to IW Ek transfer and a mesoscale to IW APE transfer followed by an IW APE to IW Ek conversion. Spatial-scale analysis of eddy–IW interaction in solutions with high-frequency forcing shows an equivalent increase in forward Ek and APE transfers inside both anticyclones and cyclones.
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Ilic, Milica, Milan Petrovic et Vladimir Stevanovic. « Boiling heat transfer modelling : A review and future prospectus ». Thermal Science 23, no 1 (2019) : 87–107. http://dx.doi.org/10.2298/tsci180725249i.
Texte intégralRésumé :
This paper reviews the current status of boiling heat transfer modelling, discusses the need for its improvement due to unresolved intriguing experimental findings and emergence of novel technical applications and outlines the directions for an advanced modelling approach. The state-of-the-art of computational boiling heat transfer studies is given for: macro-scale boiling models applied in two-fluid liquid-vapour interpenetrating media approach, micro-, meso-scale boiling computations by interface capturing methods, and nano-scale boiling simulations by molecular dynamics tools. Advantages, limitations and shortcomings of each approach, which originate from its grounding formulations, are discussed and illustrated on results obtained by the boiling model developed in our research group. Based on these issues, we stress the importance of adaptation of a multi-scale approach for development of an advanced boiling predictive methodology. A general road-map is outlined for achieving this challenging goal, which should include: improvement of existing methods for computation of boiling on different scales and development of conceptually new algorithms for linking of individual scale methods. As dramatically different time steps of integration for different boiling scales hinder the application of full multi-scale methodology on boiling problems of practical significance, we emphasise the importance of development of another algorithm for the determination of sub-domains within a macro-scale boiling region, which are relevant for conductance of small-scale simulations.
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Fareq, M., M. Fitra, Muhamad Irwanto, Syafruddin, Hs N. Gomesh, Y. M. Irwan, M. Rozailan, Suwarno et A. Herman. « A Small Scale Wireless Power Transfer ». Applied Mechanics and Materials 793 (septembre 2015) : 541–45. http://dx.doi.org/10.4028/www.scientific.net/amm.793.541.
Texte intégralRésumé :
This paper describes a small scale energy transfer by using magnetic coil made with enamel coil, which is installed on the transceiver side and function generator and RF power amplifier are installed as source to generated signal, and on the receiving side is using an enamel coil materials as antenna. In this experiment obtained energy as it travels from the transceiver can be received at the receiver side without any media or cable, the principle of electromagnetic fields used in this experiment. Number of coil inductive coupling has been compare. Number of turn 4, efficiency 91 % at 0 cm with 4.55 volt and the lower efficiency 70% at 5 cm with 3.1 volt. And number of turn 8, efficiency 97.8% at 0 cm with 4.89 volt and the lower efficiency 70% at 5 cm with 3.50 volt
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Zhou, Quan, Yong-Xiang Huang, Zhi-Ming Lu, Yu-Lu Liu et Rui Ni. « Scale-to-scale energy and enstrophy transport in two-dimensional Rayleigh–Taylor turbulence ». Journal of Fluid Mechanics 786 (2 décembre 2015) : 294–308. http://dx.doi.org/10.1017/jfm.2015.673.
Texte intégralRésumé :
We apply a recently developed filtering approach, i.e. filter-space technique (FST), to study the scale-to-scale transport of kinetic energy, thermal energy, and enstrophy in two-dimensional (2D) Rayleigh–Taylor (RT) turbulence. Although the scaling laws of the energy cascades in 2D RT systems follow the Bolgiano–Obukhov (BO59) scenario due to buoyancy forces, the kinetic energy is still found to be, on average, dynamically transferred to large scales by an inverse cascade, while both the mean thermal energy and the mean enstrophy move towards small scales by forward cascades. In particular, there is a reasonably extended range over which the transfer rate of thermal energy is scale-independent and equals the corresponding thermal dissipation rate at different times. This range functions similarly to the inertial range for the kinetic energy in the homogeneous and isotropic turbulence. Our results further show that at small scales the fluctuations of the three instantaneous local fluxes are highly asymmetrically distributed and there is a strong correlation between any two fluxes. These small-scale features are signatures of the mixing and dissipation of fluids with steep temperature gradients at the fluid interfaces.
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Biferale, L., K. Gustavsson et R. Scatamacchia. « Helicoidal particles in turbulent flows with multi-scale helical injection ». Journal of Fluid Mechanics 869 (2 mai 2019) : 646–73. http://dx.doi.org/10.1017/jfm.2019.237.
Texte intégralRésumé :
We present numerical and theoretical results concerning the properties of turbulent flows with strong multi-scale helical injection. We perform direct numerical simulations of the Navier–Stokes equations under a random helical stirring with power-law spectrum and with different intensities of energy and helicity injections. We show that there exists three different regimes where the forward energy and helicity inertial transfers are: (i) both leading with respect to the external injections, (ii) energy transfer is leading and helicity transfer is sub-leading and (iii) both are sub-leading and helicity is maximal at all scales. As a result, the cases (ii)–(iii) give flows with Kolmogorov-like inertial energy cascade and tuneable helicity transfers/contents. We further explore regime (iii) by studying its effect on the kinetics of point-like isotropic helicoids, particles whose dynamics is isotropic but breaks parity invariance. We investigate small-scale fractal clustering and preferential sampling of intense helical flow structures. Depending on their structural parameters, the isotropic helicoids either preferentially sample co-chiral or anti-chiral flow structures. We explain these findings in limiting cases in terms of what is known for spherical particles of different densities and degrees of inertia. Furthermore, we present theoretical and numerical results for a stochastic model where dynamical properties can be calculated using analytical perturbation theory. Our study shows that a suitable tuning of the stirring mechanism can strongly modify the small-scale turbulent helical properties and demonstrates that isotropic helicoids are the simplest particles able to preferentially sense helical properties in turbulence.
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BORUE, VADIM, et STEVEN A. ORSZAG. « Local energy flux and subgrid-scale statistics in three-dimensional turbulence ». Journal of Fluid Mechanics 366 (10 juillet 1998) : 1–31. http://dx.doi.org/10.1017/s0022112097008306.
Texte intégralRésumé :
Statistical properties of the subgrid-scale stress tensor, the local energy flux and filtered velocity gradients are analysed in numerical simulations of forced three-dimensional homogeneous turbulence. High Reynolds numbers are achieved by using hyperviscous dissipation. It is found that in the inertial range the subgrid-scale stress tensor and the local energy flux allow simple parametrization based on a tensor eddy viscosity. This parametrization underlines the role that negative skewness of filtered velocity gradients plays in the local energy transfer. It is found that the local energy flux only weakly correlates with the locally averaged energy dissipation rate. This fact reflects basic difficulties of large-eddy simulations of turbulence, namely the possibility of predicting the locally averaged energy dissipation rate through inertial-range quantities such as the local energy flux is limited. Statistical properties of subgrid-scale velocity gradients are systematically studied in an attempt to reveal the mechanism of local energy transfer.
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Yang, Dandan, Yanfeng Gao, Ming Yu, Xiaoping Wen et Ming-Xiang Zhao. « Analysis of drag reduction effects in turbulent Taylor–Couette flow controlled via axial oscillation of inner cylinder ». Physics of Fluids 34, no 4 (avril 2022) : 045111. http://dx.doi.org/10.1063/5.0087966.
Texte intégralRésumé :
Analysis of drag reduction effects due to axial oscillation of an inner cylinder in a turbulent Taylor–Couette (TC) flow is performed in the present study. The frictional Reynolds number on the inner cylinder is 218, and the non-dimensional oscillating period is varied from 8 to 32. By examining turbulence statistics, we uncover different impacts of the long- and short-period oscillations on the circumferential ( θ) and radial ( r) velocity fluctuations in large ([Formula: see text]) and small ([Formula: see text]) scales. One of the most surprising findings is that the short-period oscillation increases the large-scale Reynolds shear stress [Formula: see text] by the strong intensification of [Formula: see text] exceeding the suppression of [Formula: see text]. To understand the phenomena, the spectra of each term in the transport equations of the Reynolds normal stresses [Formula: see text] and [Formula: see text] are analyzed. First, it is shown that the short-period oscillation weakens the productions of [Formula: see text], and [Formula: see text] while it enhances that of [Formula: see text]. In contrast, the long-period oscillation reduces the productions of [Formula: see text] and [Formula: see text] while it mainly intensifies that of [Formula: see text]. Second, the investigations of the pressure–strain terms indicate that the short-period oscillation mainly impedes the inter-component energy transfer originating from the small-scale background turbulence. However, the long-period oscillation benefits the small-scale inter-component energy communication while it hinders the large-scale one. In addition, the inverse energy transfer in the turbulent TC flow is confirmed by inspecting the inter-scale energy transfer terms. The hindrance of the inter-scale energy transfer by the inner-cylinder oscillation plays a non-negligible role in the reduction of the wall friction drag.
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Itsweire, E. C., et K. N. Helland. « Spectra and energy transfer in stably stratified turbulence ». Journal of Fluid Mechanics 207 (octobre 1989) : 419–52. http://dx.doi.org/10.1017/s0022112089002648.
Texte intégralRésumé :
The influence of stabilizing buoyancy forces on the spectral characteristics and spectral energy transfer of grid-generated turbulence was studied in a ten-layer closed-loop stratified water channel. The results are compared to the limiting ideal cases of the three-dimensional turbulence and two-dimensional turbulence theories. The velocity power spectra evolve from a classical isotropic shape to a shape of almost k−2 after the suppression of the net vertical mixing. This final spectral shape is rather different from the k−3 to k−4 predicted by the theory of two-dimensional turbulence and could result from the interaction between small-scale internal waves and quasi-two-dimensional turbulent structures as well as some Doppler shift of advected waves. Several lengthscales are derived from the cospectra of the vertical velocity and density fluctuations and compared with the buoyancy, overturning and viscous lengthscales measured in previous studies, e.g. Stillinger, Helland & Van Atta (1983) and Itsweire, Helland & Van Atta (1986). The smallest turbulent scale, defined when the buoyancy flux goes to zero, can be related to the peak of the cospectra of the buoyancy flux. This new relationship can be used to provide a measure of the smallest turbulent scale in cases where the buoyancy flux never goes to zero, i.e. a growing turbulent stratified shear flow. Finally, the one-dimensional energy transfer term computed from the bispectra shows evidence of a reverse energy cascade from the small scales to the large scales far from the grid where buoyancy forces dominate inertial forces. The observed reverse energy transfer could be produced by the development of quasi-two-dimensional eddies as the original three-dimensional turbulence collapses.
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Dong, Zhonghao, Xiaofeng Lu, Rongdi Zhang, Jianbo Li, Zhaoliang Wu, Zhicun Liu, Yanting Yang, Quanhai Wang et Yinhu Kang. « Methods and Applications of Full-Scale Field Testing for Large-Scale Circulating Fluidized Bed Boilers ». Energies 17, no 4 (14 février 2024) : 889. http://dx.doi.org/10.3390/en17040889.
Texte intégralRésumé :
Circulating fluidized bed (CFB) boilers offer a technically viable and environmentally friendly means for the clean and efficient utilization of solid fuels. However, the complex gas–solid two-phase flow processes within them have hindered a thorough resolution of prediction issues related to coupled combustion, heat transfer, and pollutant generation characteristics. To address the deficiencies in scientific research, meet the practical operational needs of CFB boilers, and comply with new carbon emission policies, conducting full-scale field tests on large-scale CFB boilers is needed, so that the complex gas–solid flow, combustion, and heat transfer mechanisms in the furnace can be comprehended. In this paper, issues related to large-scale CFB boilers, including the uniformity of air distribution, secondary air injection range, spatial distribution of oxygen consumption and combustion reactions, distribution of pollutant generation, hydrodynamic and heat transfer characteristics, coal feeding distribution characteristics, coal diffusion characteristics under thermal operating conditions, and engineering research on anti-wear technology, are reviewed. By integrating practical engineering applications, the basic methods and measurement techniques used in full-scale field tests for large-scale CFB boilers are summarized, providing a practical reference for conducting engineering tests with large-scale CFB boilers.
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Sun, Oliver M., et Robert Pinkel. « Energy Transfer from High-Shear, Low-Frequency Internal Waves to High-Frequency Waves near Kaena Ridge, Hawaii ». Journal of Physical Oceanography 42, no 9 (11 avril 2012) : 1524–47. http://dx.doi.org/10.1175/jpo-d-11-0117.1.
Texte intégralRésumé :
Abstract Evidence is presented for the transfer of energy from low-frequency inertial–diurnal internal waves to high-frequency waves in the band between 6 cpd and the buoyancy frequency. This transfer links the most energetic waves in the spectrum, those receiving energy directly from the winds, barotropic tides, and parametric subharmonic instability, with those most directly involved in the breaking process. Transfer estimates are based on month-long records of ocean velocity and temperature obtained continuously over 80–800 m from the research platform (R/P) Floating Instrument Platform (FLIP) in the Hawaii Ocean Mixing Experiment (HOME) Nearfield (2002) and Farfield (2001) experiments, in Hawaiian waters. Triple correlations between low-frequency vertical shears and high-frequency Reynolds stresses, 〈uiw∂Ui/∂z〉, are used to estimate energy transfers. These are supported by bispectral analysis, which show significant energy transfers to pairs of waves with nearly identical frequency. Wavenumber bispectra indicate that the vertical scales of the high-frequency waves are unequal, with one wave of comparable scale to that of the low-frequency parent and the other of much longer scale. The scales of the high-frequency waves contrast with the classical pictures of induced diffusion and elastic scattering interactions and violates the scale-separation assumption of eikonal models of interaction. The possibility that the observed waves are Doppler shifted from intrinsic frequencies near f or N is explored. Peak transfer rates in the Nearfield, an energetic tidal conversion site, are on the order of 2 × 10−7 W kg−1 and are of similar magnitude to estimates of turbulent dissipation that were made near the ridge during HOME. Transfer rates in the Farfield are found to be about half the Nearfield values.
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Solovej, V., K. Gorbunov, V. Vereshchak et O. Gorbunova. « RESEARCH OF EXTERNAL MASS TRANSFER PROCESSES FOR ADSORPTION FROM SOLUTIONS IN A APPARATUS WITH STIRRING ». Integrated Technologies and Energy Saving, no 1 (6 juillet 2021) : 11–20. http://dx.doi.org/10.20998/2078-5364.2021.1.02.
Texte intégralRésumé :
A study has been mode of transport-controlled mass transfer-controlled to particles suspended in a stirred vessel. The motion of particle in a fluid was examined and a method of predicting relative velocities in terms of Kolmogoroff’s theory of local isotropic turbulence for mass transfer was outlined.
To provide a more concrete visualization of complex wave form of turbulence, the concepts of eddies, of eddy velocity, scale (or wave number) and energy spectrum, have proved convenient.
Large scale motions of scale contain almost all of the energy and they are directly responsible for energy diffusion throughout the stirring vessel by kinetic and pressure energies. However, almost no energy is dissipated by the large-scale energy-containing eddies. A scale of motion less than is responsible for convective energy transfer to even smaller eddy sires. At still smaller eddy scales, close to a characteristic microscale, both viscous energy dissipation and convection are the rule. The last range of eddies has been termed the universal equilibrium range. It has been further divided into a low eddy size region, the viscous dissipation subrange, and a larger eddy size region, the inertial convection subrange.
Measurements of energy spectrum in mixing vessel are shown that there is a range, where the so called -(5/3) power law is effective. Accordingly, the theory of local isotropy of Kolmogoroff can be applied because existence of the internal subrange. As the integrated value of local energy dissipation rate agrees with the power per unit mass of liquid from the impeller, almost all energy from the impeller is viscous dissipated in eddies of microscale.
The correlation for mass transfer to particles suspended in a stirred vessel is recommended. The results of experimental study are approximately 12 % above the predicted values.
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AKHAVAN, R., A. ANSARI, S. KANG et N. MANGIAVACCHI. « Subgrid-scale interactions in a numerically simulated planar turbulent jet and implications for modelling ». Journal of Fluid Mechanics 408 (10 avril 2000) : 83–120. http://dx.doi.org/10.1017/s0022112099007582.
Texte intégralRésumé :
The dynamics of subgrid-scale energy transfer in turbulence is investigated in a database of a planar turbulent jet at Reλ ≈ 110, obtained by direct numerical simulation. In agreement with analytical predictions (Kraichnan 1976), subgrid-scale energy transfer is found to arise from two effects: one involving non-local interactions between the resolved scales and disparate subgrid scales, the other involving local interactions between the resolved and subgrid scales near the cutoff. The former gives rise to a positive, wavenumber-independent eddy-viscosity distribution in the spectral space, and is manifested as low-intensity, forward transfers of energy in the physical space. The latter gives rise to positive and negative cusps in the spectral eddy-viscosity distribution near the cutoff, and appears as intense and coherent regions of forward and reverse transfer of energy in the physical space. Only a narrow band of subgrid wavenumbers, on the order of a fraction of an octave, make the dominant contributions to the latter. A dynamic two-component subgrid-scale model (DTM), incorporating these effects, is proposed. In this model, the non-local forward transfers of energy are parameterized using an eddy-viscosity term, while the local interactions are modelled using the dynamics of the resolved scales near the cutoff. The model naturally accounts for backscatter and correctly predicts the breakdown of the net transfer into forward and reverse contributions in a priori tests. The inclusion of the local-interactions term in DTM significantly reduces the variability of the model coefficient compared to that in pure eddy-viscosity models. This eliminates the need for averaging the model coefficient, making DTM well-suited to computations of complex-geometry flows. The proposed model is evaluated in LES of transitional and turbulent jet and channel flows. The results show DTM provides more accurate predictions of the statistics, structure, and spectra than dynamic eddy-viscosity models and remains robust at marginal LES resolutions.
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Nikurashin, Maxim, et Sonya Legg. « A Mechanism for Local Dissipation of Internal Tides Generated at Rough Topography ». Journal of Physical Oceanography 41, no 2 (1 février 2011) : 378–95. http://dx.doi.org/10.1175/2010jpo4522.1.
Texte intégralRésumé :
Abstract Fine- and micro-structure observations indicate that turbulent mixing is enhanced within O(1) km above rough topography. Enhanced mixing is associated with internal wave breaking and, in many regions of the ocean, has been linked to the breaking and dissipation of internal tides. The generation and dissipation of internal tides are explored in this study using a high-resolution two-dimensional nonhydrostatic numerical model, which explicitly resolves the instabilities leading to wave breaking, configured in an idealized domain with a realistic multiscale topography and flow characteristics. The control simulation, chosen to represent the Brazil Basin region, produces a vertical profile of energy dissipation and temporal characteristics of finescale motions that are consistent with observations. Results suggest that a significant fraction of mixing in the bottom O(1) km of the ocean is sustained by the transfer of energy from the large-scale internal tides to smaller-scale internal waves by nonlinear wave–wave interactions. The time scale of the energy transfer to the smaller scales is estimated to be on the order of a few days. A suite of sensitivity experiments is carried out to examine the dependence of the energy transfer time scale and energy dissipation on topographic roughness, tidal amplitude, and Coriolis frequency parameters. Implications for tidal mixing parameterizations are discussed.
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Yang, Junyu, Qianghui Xu, Xuan Kou, Geng Wang, Timan Lei, Yi Wang, Xiaosen Li et Kai H. Luo. « Three-dimensional pore-scale study of methane hydrate dissociation mechanisms based on micro-CT images ». Innovation Energy 1, no 1 (2024) : 100015. http://dx.doi.org/10.59717/j.xinn-energy.2024.100015.
Texte intégralRésumé :
<p>Methane hydrate is a promising source of alternative energy. An in-depth understanding of the hydrate dissociation mechanism is crucial for the efficient extraction. In the present work, a comprehensive set of pore-scale numerical studies of hydrate dissociation mechanisms is presented. Pore-scale lattice Boltzmann (LB) models are proposed to simulate the multiphysics process during methane hydrate dissociation. The numerical simulations employ the actual hydrate sediment pore structure obtained by the micro-CT imaging. Experimental results of xenon hydrate dissociation are compared with the numerical simulations, indicating that the observed hydrate pore habits evolution is accurately captured by the proposed LB models. Furthermore, simulations of methane hydrate dissociation under different sediment water saturations, fluid flow rates and thermal conditions are conducted. Heat and mass transfer limitations both have significant effects on the methane hydrate dissociation rate. The bubble movement can further influence the dissociation process. Dissociation patterns can be divided into three categories, uniform, non-uniform and wormholing. The fluid flow impacts hydrate dissociation rates differently in three-dimensional real structures compared to two-dimensional idealized ones, influenced by variations in hydrate pore habits and flow properties. Finally, upscaling investigations are conducted to provide the permeability and kinetic models for the representative elementary volume (REV)-scale production forecast. Due to the difference in the hydrate pore habits and dissociation mechanisms, the three-dimensional upscaling results contrast with prior findings from two-dimensional studies. The present work provides a paradigm for pore-scale numerical simulation studies on the hydrate dissociation, which can offer theoretical guidance on efficient hydrate extraction.</p>
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Alves Portela, F., G. Papadakis et J. C. Vassilicos. « The turbulence cascade in the near wake of a square prism ». Journal of Fluid Mechanics 825 (20 juillet 2017) : 315–52. http://dx.doi.org/10.1017/jfm.2017.390.
Texte intégralRésumé :
We present a study of the turbulence cascade on the centreline of an inhomogeneous and anisotropic near-field turbulent wake generated by a square prism at a Reynolds number of$Re=3900$using the Kármán–Howarth–Monin–Hill equation. This is the fully generalised scale-by-scale energy balance which, unlike the Kármán–Howarth equation, does not require homogeneity or isotropy assumptions. Our data are obtained from a direct numerical simulation and therefore enable us to access all of the processes involved in this energy balance. A significant range of length scales exists where the orientation-averaged nonlinear interscale transfer rate is approximately constant and negative, indicating a forward turbulence cascade on average. This average cascade consists of coexisting forward and inverse cascade behaviours in different scale-space orientations. With increasing distance from the prism but within the near field of the wake, the orientation-averaged nonlinear interscale transfer rate tends to be approximately equal to minus the turbulence dissipation rate even though all of the inhomogeneity-related energy processes in the scale-by-scale energy balance are significant, if not equally important. We also find well-defined near$-5/3$energy spectra in the streamwise direction, in particular at a centreline position where the inverse cascade behaviour occurs for streamwise oriented length scales.
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Isaev, S. A., A. I. Leontiev, D. V. Nikushchenko, D. Kong, K. M. Chung et A. G. Sudakov. « Vortex heat transfer enhancement by energy-efficient structured plates with zigzag grooves for micro- and macro-scale energy and electronic devices ». Journal of Physics : Conference Series 2150, no 1 (1 janvier 2022) : 012004. http://dx.doi.org/10.1088/1742-6596/2150/1/012004.
Texte intégralRésumé :
Abstract An energy-efficient flat surface is formed when applying single-row cross-flow zigzag grooves (VVVVVV) in a dense arrangement. Convective heat transfer is considered in turbulent flow around a longitudinal fragment of a plate with a length of 40 and a width of 4 with a package of 14 singlerow inclined backslash(\)-shaped grooves with symmetry conditions at the lateral boundaries. The width of the grooves is 1, the depth is 0.25, the edge rounding radius is 0.2, the angles of inclination are 30°, 45°, 50° and 60°, the pitch is 2.4, the Reynolds number is 104, and the thickness of the incoming boundary layer is 0.175. The phenomenon of anomalous enhancement of the separation flow and heat transfer in zigzag grooves and acceleration of the wall flow discovered in inclined oval-trench dimples has been confirmed.
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Deschamps, Thomas, Mohamed Kanniche, Laurent Grandjean et Olivier Authier. « Modeling of Vacuum Temperature Swing Adsorption for Direct Air Capture Using Aspen Adsorption ». Clean Technologies 4, no 2 (8 avril 2022) : 258–75. http://dx.doi.org/10.3390/cleantechnol4020015.
Texte intégralRésumé :
The paper evaluates the performance of an adsorption-based technology for CO2 capture directly from the air at the industrial scale. The approach is based on detailed mass and energy balance dynamic modeling of the vacuum temperature swing adsorption (VTSA) process in Aspen Adsorption software. The first step of the approach aims to validate the modeling thanks to published experimental data for a lab-scale bed module in terms of mass transfer and energy performance on a packed bed using amine-functionalized material. A parametric study on the main operating conditions, i.e., air velocity, air relative moisture, air temperature, and CO2 capture rate, is undertaken to assess the global performance and energy consumption. A method of up-scaling the lab-scale bed module to industrial module is exposed and mass transfer and energy performances of the industrial module are provided. The scale up from lab scale to the industrial size is conservative in terms of thermal energy consumption while the electrical consumption is very sensitive to the bed design. Further study related to the engineering solutions available to reach high global gas velocity are required. This could be offered by monolith-shape adsorbents.
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Sun, Shouzheng, Zhenyu Han et Hongya Fu. « Multi-Scale Energy Analysis Method during Automated Fibre Placement Process ». Advanced Composites Letters 26, no 4 (juillet 2017) : 096369351702600. http://dx.doi.org/10.1177/096369351702600404.
Texte intégralRésumé :
Automated fibre placement (AFP) is an advanced technology for composite lay-up. However, analysis on mechanical properties used by experiments or macroscopic theories during AFP process suffers from some restrictions, because multi-scale effect of laying tows and their manufacturing defects could not be considered. This contribution proposes a novel anti-sequential multi-scale analysis method based on concurrent/sequential multi-scale analysis method. In order to establish a coupling mechanism among different scales, multi-scale energy transfer model is presented and emphatically analysed through composite mechanics and classical mechanics. Furthermore, taking a Bisphenol A epoxy matrix prepreg tow as an example, an application is employed to verify the feasibility of the method and model. Finally, application field for processing optimization is introduced and prospected.
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Thallmair, Sebastian, et Siewert J. Marrink. « Chromophore arrangement in light-harvesting complex II influenced by the protein dynamics on the microsecond time scale ». EPJ Web of Conferences 205 (2019) : 09039. http://dx.doi.org/10.1051/epjconf/201920509039.
Texte intégralRésumé :
Coarse-grained molecular dynamics simulations of light-harvesting complex II in thylakoid membrane reveal its microsecond dynamics. We analyze the fluctuations of the relative chromophore orientations which set the stage for the energy transfer.