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Auteur : Grafiati
Publié le 20 avril 2024

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1

Teixeira, M. A. C., et C. B. da Silva. « Turbulence dynamics near a turbulent/non-turbulent interface ». Journal of Fluid Mechanics 695 (13 février 2012) : 257–87. http://dx.doi.org/10.1017/jfm.2012.17.

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AbstractThe characteristics of the boundary layer separating a turbulence region from an irrotational (or non-turbulent) flow region are investigated using rapid distortion theory (RDT). The turbulence region is approximated as homogeneous and isotropic far away from the bounding turbulent/non-turbulent (T/NT) interface, which is assumed to remain approximately flat. Inviscid effects resulting from the continuity of the normal velocity and pressure at the interface, in addition to viscous effects resulting from the continuity of the tangential velocity and shear stress, are taken into account by considering a sudden insertion of the T/NT interface, in the absence of mean shear. Profiles of the velocity variances, turbulent kinetic energy (TKE), viscous dissipation rate ($\varepsilon $), turbulence length scales, and pressure statistics are derived, showing an excellent agreement with results from direct numerical simulations (DNS). Interestingly, the normalized inviscid flow statistics at the T/NT interface do not depend on the form of the assumed TKE spectrum. Outside the turbulent region, where the flow is irrotational (except inside a thin viscous boundary layer),$\varepsilon $decays as${z}^{\ensuremath{-} 6} $, where$z$is the distance from the T/NT interface. The mean pressure distribution is calculated using RDT, and exhibits a decrease towards the turbulence region due to the associated velocity fluctuations, consistent with the generation of a mean entrainment velocity. The vorticity variance and$\varepsilon $display large maxima at the T/NT interface due to the inviscid discontinuities of the tangential velocity variances existing there, and these maxima are quantitatively related to the thickness$\delta $of the viscous boundary layer (VBL). For an equilibrium VBL, the RDT analysis suggests that$\delta \ensuremath{\sim} \eta $(where$\eta $is the Kolmogorov microscale), which is consistent with the scaling law identified in a very recent DNS study for shear-free T/NT interfaces.
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2

Westerweel, Jerry, Alberto Petracci, René Delfos et Julian C. R. Hunt. « Characteristics of the turbulent/non-turbulent interface of a non-isothermal jet ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 369, no 1937 (28 février 2011) : 723–37. http://dx.doi.org/10.1098/rsta.2010.0308.

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The turbulent/non-turbulent interface of a jet is characterized by sharp jumps (‘discontinuities’) in the conditional flow statistics relative to the interface. Experiments were carried out to measure the conditional flow statistics for a non-isothermal jet, i.e. a cooled jet. These experiments are complementary to previous experiments on an isothermal Re =2000 jet, where, in the present experiments on a non-isothermal jet, the thermal diffusivity is intermediate to the diffusivity of momentum and the diffusivity of mass. The experimental method is a combined laser-induced fluorescence/particle image velocimetry method, where a temperature-sensitive fluorescent dye (rhodamine 6G) is used to measure the instantaneous temperature fluctuations. The results show that the cooled jet can be considered to behave like a self-similar jet without any significant buoyancy effects. The detection of the interface is based on the instantaneous temperature, and provides a reliable means to detect the interface. Conditional flow statistics reveal the superlayer jump in the conditional vorticity and in the temperature.
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Watanabe, T., X. Zhang et K. Nagata. « Turbulent/non-turbulent interfaces detected in DNS of incompressible turbulent boundary layers ». Physics of Fluids 30, no 3 (mars 2018) : 035102. http://dx.doi.org/10.1063/1.5022423.

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4

Yu, Jia-Long, et Xi-Yun Lu. « Topological evolution near the turbulent/non-turbulent interface in turbulent mixing layer ». Journal of Turbulence 20, no 5 (4 mai 2019) : 300–321. http://dx.doi.org/10.1080/14685248.2019.1640368.

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5

Steiner, Helfried, et Christian Walchshofer. « Small-scale mixing at the turbulent/non-turbulent interface in turbulent jets ». PAMM 11, no 1 (décembre 2011) : 601–2. http://dx.doi.org/10.1002/pamm.201110290.

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6

BISSET, DAVID K., JULIAN C. R. HUNT et MICHAEL M. ROGERS. « The turbulent/non-turbulent interface bounding a far wake ». Journal of Fluid Mechanics 451 (25 janvier 2002) : 383–410. http://dx.doi.org/10.1017/s0022112001006759.

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The velocity fields of a turbulent wake behind a flat plate obtained from the direct numerical simulations of Moser et al. (1998) are used to study the structure of the flow in the intermittent zone where there are, alternately, regions of fully turbulent flow and non-turbulent velocity fluctuations on either side of a thin randomly moving interface. Comparisons are made with a wake that is ‘forced’ by amplifying initial velocity fluctuations. A temperature field T, with constant values of 1.0 and 0 above and below the wake, is transported across the wake as a passive scalar. The value of the Reynolds number based on the centreplane mean velocity defect and half-width b of the wake is Re ≈ 2000.The thickness of the continuous interface is about 0.07b, whereas the amplitude of fluctuations of the instantaneous interface displacement yI(t) is an order of magnitude larger, being about 0.5b. This explains why the mean statistics of vorticity in the intermittent zone can be calculated in terms of the probability distribution of yI and the instantaneous discontinuity in vorticity across the interface. When plotted as functions of y−yI the conditional mean velocity 〈U〉 and temperature 〈T〉 profiles show sharp jumps at the interface adjacent to a thick zone where 〈U〉 and 〈T〉 vary much more slowly.Statistics for the conditional vorticity and velocity variances, available in such detail only from DNS data, show how streamwise and spanwise components of vorticity are generated by vortex stretching in the bulges of the interface. While mean Reynolds stresses (in the fixed reference frame) decrease gradually in the intermittent zone, conditional stresses are roughly constant and then decrease sharply towards zero at the interface. Flow fields around the interface, analysed in terms of the local streamline pattern, confirm and explain previous results that the advancement of the vortical interface into the irrotational flow is driven by large-scale eddy motion.Terms used in one-point turbulence models are evaluated both conventionally and conditionally in the interface region, and the current practice in statistical models of approximating entrainment by a diffusion process is assessed.
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7

Neuhaus, Lars, Matthias Wächter et Joachim Peinke. « The fractal turbulent–non-turbulent interface in the atmosphere ». Wind Energy Science 9, no 2 (22 février 2024) : 439–52. http://dx.doi.org/10.5194/wes-9-439-2024.

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Abstract. With their constant increase in size, wind turbines are reaching unprecedented heights. Therefore, at these heights, they are influenced by wind conditions that have not yet been studied in detail. With increasing height, a transition to laminar conditions becomes more and more likely. In this paper, the presence of the turbulent–non-turbulent interface (TNTI) in the atmosphere is investigated. Three different on- and offshore locations are investigated. Our fractal scaling analysis leads to typical values known from ideal laboratory and numerical studies. The height distribution of the probability of the TNTI is determined and shows a frequent occurrence at the height of the rotor of future multi-megawatt turbines. The indicated universality of the fractality of the TNTI allows the use of simplified models in laboratory and numerical investigations.
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8

Zhang, Xinxian, Tomoaki Watanabe et Koji Nagata. « Passive scalar mixing near turbulent/non-turbulent interface in compressible turbulent boundary layers ». Physica Scripta 94, no 4 (30 janvier 2019) : 044002. http://dx.doi.org/10.1088/1402-4896/aafbdf.

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9

Yang, Jongmin, Min Yoon et Hyung Jin Sung. « The turbulent/non-turbulent interface in an adverse pressure gradient turbulent boundary layer ». International Journal of Heat and Fluid Flow 86 (décembre 2020) : 108704. http://dx.doi.org/10.1016/j.ijheatfluidflow.2020.108704.

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10

PAPARELLA, F., et W. R. YOUNG. « Horizontal convection is non-turbulent ». Journal of Fluid Mechanics 466 (10 septembre 2002) : 205–14. http://dx.doi.org/10.1017/s0022112002001313.

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Consider the problem of horizontal convection: a Boussinesq fluid, forced by applying a non-uniform temperature at its top surface, with all other boundaries insulating. We prove that if the viscosity, ν, and thermal diffusivity, κ, are lowered to zero, with σ ≡ ν/κ fixed, then the energy dissipation per unit mass, κ, also vanishes in this limit. Numerical solutions of the two-dimensional case show that despite this anti-turbulence theorem, horizontal convection exhibits a transition to eddying flow, provided that the Rayleigh number is sufficiently high, or the Prandtl number σ sufficiently small. We speculate that horizontal convection is an example of a flow with a large number of active modes which is nonetheless not ‘truly turbulent’ because ε→0 in the inviscid limit.
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11

Waggett, RJ, et EJ Buskey. « Copepod escape behavior in non-turbulent and turbulent hydrodynamic regimes ». Marine Ecology Progress Series 334 (26 mars 2007) : 193–98. http://dx.doi.org/10.3354/meps334193.

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12

Nagata, R., T. Watanabe et K. Nagata. « Turbulent/non-turbulent interfaces in temporally evolving compressible planar jets ». Physics of Fluids 30, no 10 (octobre 2018) : 105109. http://dx.doi.org/10.1063/1.5047395.

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13

Borrell, Guillem, et Javier Jiménez. « Properties of the turbulent/non-turbulent interface in boundary layers ». Journal of Fluid Mechanics 801 (26 juillet 2016) : 554–96. http://dx.doi.org/10.1017/jfm.2016.430.

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The turbulent/non-turbulent interface is analysed in a direct numerical simulation of a boundary layer in the Reynolds number range$Re_{{\it\theta}}=2800{-}6600$, with emphasis on the behaviour of the relatively large-scale fractal intermittent region. This requires the introduction of a new definition of the distance between a point and a general surface, which is compared with the more usual vertical distance to the top of the layer. Interfaces are obtained by thresholding the enstrophy field and the magnitude of the rate-of-strain tensor, and it is concluded that, while the former are physically relevant features, the latter are not. By varying the threshold, a topological transition is identified as the interface moves from the free stream into the turbulent core. A vorticity scale is defined which collapses that transition for different Reynolds numbers, roughly equivalent to the root-mean-squared vorticity at the edge of the boundary layer. Conditionally averaged flow variables are analysed as functions of the new distance, both within and outside the interface. It is found that the interface contains a non-equilibrium layer whose thickness scales well with the Taylor microscale, enveloping a self-similar layer spanning a fixed fraction of the boundary-layer thickness. Interestingly, the straining structure of the flow is similar in both regions. Irrotational pockets within the turbulent core are also studied. They form a self-similar set whose size decreases with increasing depth, presumably due to breakup by the turbulence, but the rate of viscous diffusion is independent of the pocket size. The raw data used in the analysis are freely available from our web page (http://torroja.dmt.upm.es).
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14

Chauhan, Kapil, Jimmy Philip et Ivan Marusic. « Scaling of the turbulent/non-turbulent interface in boundary layers ». Journal of Fluid Mechanics 751 (19 juin 2014) : 298–328. http://dx.doi.org/10.1017/jfm.2014.298.

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AbstractScaling of the interface that demarcates a turbulent boundary layer from the non-turbulent free stream is sought using theoretical reasoning and experimental evidence in a zero-pressure-gradient boundary layer. The data-analysis, utilising particle image velocimetry (PIV) measurements at four different Reynolds numbers ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\delta u_{\tau }/\nu =1200\mbox{--}14\, 500$), indicates the presence of a viscosity dominated interface at all Reynolds numbers. It is found that the mean normal velocity across the interface and the tangential velocity jump scale with the skin-friction velocity$u_{\tau }$and are approximately$u_{\tau }/10$and$u_{\tau }$, respectively. The width of the superlayer is characterised by the local vorticity thickness$\delta _{\omega }$and scales with the viscous length scale$\nu /u_{\tau }$. An order of magnitude analysis of the tangential momentum balance within the superlayer suggests that the turbulent motions also scale with inner velocity and length scales$u_{\tau }$and$\nu /u_{\tau }$, respectively. The influence of the wall on the dynamics in the superlayer is considered via Townsend’s similarity hypothesis, which can be extended to account for the viscous influence at the turbulent/non-turbulent interface. Similar to a turbulent far-wake the turbulent motions in the superlayer are of the same order as the mean velocity deficit, which lends to a physical explanation for the emergence of the wake profile in the outer part of the boundary layer.
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15

Watanabe, T., Y. Sakai, K. Nagata, Y. Ito et T. Hayase. « Turbulent mixing of passive scalar near turbulent and non-turbulent interface in mixing layers ». Physics of Fluids 27, no 8 (août 2015) : 085109. http://dx.doi.org/10.1063/1.4928199.

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16

Wu, Di, JinJun Wang, GuangYao Cui et Chong Pan. « Effects of surface shapes on properties of turbulent/non-turbulent interface in turbulent boundary layers ». Science China Technological Sciences 63, no 2 (6 juin 2019) : 214–22. http://dx.doi.org/10.1007/s11431-018-9434-5.

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17

Westerweel, J., T. Hofmann, C. Fukushima et J. Hunt. « The turbulent/non-turbulent interface at the outer boundary of a self-similar turbulent jet ». Experiments in Fluids 33, no 6 (décembre 2002) : 873–78. http://dx.doi.org/10.1007/s00348-002-0489-5.

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18

Ishihara, Takashi, Hiroki Ogasawara et Julian C. R. Hunt. « Analysis of conditional statistics obtained near the turbulent/non-turbulent interface of turbulent boundary layers ». Journal of Fluids and Structures 53 (février 2015) : 50–57. http://dx.doi.org/10.1016/j.jfluidstructs.2014.10.008.

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19

Elsinga, G. E., et C. B. da Silva. « How the turbulent/non-turbulent interface is different from internal turbulence ». Journal of Fluid Mechanics 866 (5 mars 2019) : 216–38. http://dx.doi.org/10.1017/jfm.2019.85.

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The average patterns of the velocity and scalar fields near turbulent/non-turbulent interfaces (TNTI), obtained from direct numerical simulations (DNS) of planar turbulent jets and shear free turbulence, are assessed in the strain eigenframe. These flow patterns help to clarify many aspects of the flow dynamics, including a passive scalar, near a TNTI layer, that are otherwise not easily and clearly assessed. The averaged flow field near the TNTI layer exhibits a saddle-node flow topology associated with a vortex in one half of the interface, while the other half of the interface consists of a shear layer. This observed flow pattern is thus very different from the shear-layer structure consisting of two aligned vortical motions bounded by two large-scale regions of uniform flow, that typically characterizes the average strain field in the fully developed turbulent regions. Moreover, strain dominates over vorticity near the TNTI layer, in contrast to internal turbulence. Consequently, the most compressive principal straining direction is perpendicular to the TNTI layer, and the characteristic 45-degree angle displayed in internal shear layers is not observed at the TNTI layer. The particular flow pattern observed near the TNTI layer has important consequences for the dynamics of a passive scalar field, and explains why regions of particularly high scalar gradient (magnitude) are typically found at TNTIs separating fluid with different levels of scalar concentration. Finally, it is demonstrated that, within the fully developed internal turbulent region, the scalar gradient exhibits an angle with the most compressive straining direction with a peak probability at around 20$^{\text{o}}$. The scalar gradient and the most compressive strain are not preferentially aligned, as has been considered for many years. The misconception originated from an ambiguous definition of the positive directions of the strain eigenvectors.
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Ferrey, P., et B. Aupoix. « Behaviour of turbulence models near a turbulent/non-turbulent interface revisited ». International Journal of Heat and Fluid Flow 27, no 5 (octobre 2006) : 831–37. http://dx.doi.org/10.1016/j.ijheatfluidflow.2006.03.022.

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Watanabe, Tomoaki, Carlos B. da Silva, Yasuhiko Sakai, Koji Nagata et Toshiyuki Hayase. « Lagrangian properties of the entrainment across turbulent/non-turbulent interface layers ». Physics of Fluids 28, no 3 (mars 2016) : 031701. http://dx.doi.org/10.1063/1.4942959.

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Chauhan, Kapil, Jimmy Philip, Charitha M. de Silva, Nicholas Hutchins et Ivan Marusic. « The turbulent/non-turbulent interface and entrainment in a boundary layer ». Journal of Fluid Mechanics 742 (21 février 2014) : 119–51. http://dx.doi.org/10.1017/jfm.2013.641.

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AbstractThe turbulent/non-turbulent interface in a zero-pressure-gradient turbulent boundary layer at high Reynolds number ($\mathit{Re}_\tau =14\, 500$) is examined using particle image velocimetry. An experimental set-up is utilized that employs multiple high-resolution cameras to capture a large field of view that extends $2\delta \times 1.1\delta $ in the streamwise/wall-normal plane with an unprecedented dynamic range. The interface is detected using a criteria of local turbulent kinetic energy and proves to be an effective method for boundary layers. The presence of a turbulent/non-turbulent superlayer is corroborated by the presence of a jump for the conditionally averaged streamwise velocity across the interface. The steep change in velocity is accompanied by a discontinuity in vorticity and a sharp rise in the Reynolds shear stress. The conditional statistics at the interface are in quantitative agreement with the superlayer equations outlined by Reynolds (J. Fluid Mech., vol. 54, 1972, pp. 481–488). Further analysis introduces the mass flux as a physically relevant parameter that provides a direct quantitative insight into the entrainment. Consistency of this approach is first established via the equality of mean entrainment calculations obtained using three different methods, namely, conditional, instantaneous and mean equations of motion. By means of ‘mass-flux spectra’ it is shown that the boundary-layer entrainment is characterized by two distinctive length scales which appear to be associated with a two-stage entrainment process and have a substantial scale separation.
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Krug, Dominik, Markus Holzner, Beat Lüthi, Marc Wolf, Wolfgang Kinzelbach et Arkady Tsinober. « The turbulent/non-turbulent interface in an inclined dense gravity current ». Journal of Fluid Mechanics 765 (20 janvier 2015) : 303–24. http://dx.doi.org/10.1017/jfm.2014.738.

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AbstractWe present an experimental investigation of entrainment and the dynamics near the turbulent/non-turbulent interface in a dense gravity current. The main goal of the study is to investigate changes in the interfacial physics due to the presence of stratification and to examine their impact on the entrainment rate. To this end, three-dimensional data sets of the density and the velocity fields are obtained through a combined scanning particle tracking velocimetry/laser-induced fluorescence approach for two different stratification levels with inflow Richardson numbers of $\mathit{Ri}_{0}=0.23$ and $\mathit{Ri}_{0}=0.46$, respectively, at a Reynolds number around $\mathit{Re}_{0}=3700$. An analysis conditioned on the instantaneous position of the turbulent/non-turbulent interface as defined by a threshold on enstrophy reveals an interfacial region that is in many aspects independent of the initial level of stratification. This is reflected most prominently in matching peaks of the gradient Richardson number $\mathit{Ri}_{g}\approx 0.1$ located approximately $10{\it\eta}$ from the position of the interface inside the turbulent region, where ${\it\eta}=({\it\nu}^{3}/{\it\epsilon})^{1/4}$ is the Kolmogorov scale, and ${\it\nu}$ and ${\it\epsilon}$ denote the kinematic viscosity and the rate of turbulent dissipation, respectively. A possible explanation for this finding is offered in terms of a cyclic evolution in the interaction of stratification and shear involving the buildup of density and velocity gradients through inviscid amplification and their subsequent depletion through molecular effects and pressure. In accordance with the close agreement of the interfacial properties for the two cases, no significant differences were found for the local entrainment velocity, $v_{n}$ (defined as the propagation velocity of an enstrophy isosurface relative to the fluid), at different initial stratification levels. Moreover, we find that the baroclinic torque does not contribute significantly to the local entrainment velocity. Comparing results for the surface area of the convoluted interface to estimates from fractal scaling theory, we identify differences in the interface geometry as the major factor in the reduction of the entrainment rate due to density stratification.
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Devenish, B. J., et D. J. Thomson. « Non-Gaussianity in turbulent relative dispersion ». Journal of Fluid Mechanics 867 (29 mars 2019) : 877–905. http://dx.doi.org/10.1017/jfm.2019.114.

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We present an extension of Thomson’s (J. Fluid Mech., vol. 210, 1990, pp. 113–153) two-particle Lagrangian stochastic model that is constructed to be consistent with the $4/5$ law of turbulence. The rate of separation in the new model is reduced relative to the original model with zero skewness in the Eulerian longitudinal relative velocity distribution and is close to recent measurements from direct numerical simulations of homogeneous isotropic turbulence. The rate of separation in the equivalent backwards dispersion model is approximately a factor of 2.9 larger than the forwards dispersion model, a result that is consistent with previous work.
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Mastorakos, Epaminondas. « Ignition of turbulent non-premixed flames ». Progress in Energy and Combustion Science 35, no 1 (février 2009) : 57–97. http://dx.doi.org/10.1016/j.pecs.2008.07.002.

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26

Scotti, A., et B. White. « Is horizontal convection really “non-turbulent?” ». Geophysical Research Letters 38, no 21 (novembre 2011) : n/a. http://dx.doi.org/10.1029/2011gl049701.

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Zecchetto, Marco, Tomoaki Watanabe, Koji Nagata et Carlos B. da Silva. « Turbulent/non-turbulent interfaces in equilibrium and non-equilibrium regions in the absence of mean shear ». International Journal of Heat and Fluid Flow 103 (octobre 2023) : 109198. http://dx.doi.org/10.1016/j.ijheatfluidflow.2023.109198.

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KRAEV, Viacheslav. « Experimental research of turbulent flow frequency spectra ». INCAS BULLETIN 12, no 2 (5 juin 2020) : 87–97. http://dx.doi.org/10.13111/2066-8201.2020.12.2.8.

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Hydraulic and heat transfer processes play a very important role in the design and prototyping of aerospace technology. In most cases this technique works under non-isothermal conditions. Non-isothermal conditions may significantly affect heat transfer and hydrodynamic process. Fundamental research of Non-isothermal turbulent flow is required for further engineering modeling. Models for unsteady processes calculation must be based on fundamental turbulent structure research. Moscow Aviation Institute National Research University (MAI) has been building non-isothermal turbulent flow structures since 1989. An experimental facility was designed to provide gas flow heating. Experimental data of a turbulent gas flow structure in isothermal and non-isothermal conditions are presented. The frequency spectra of axial and radial velocity pulsations are based on experimental data received. The results of experimental turbulent flow research demonstrate fundamental non-isothermal processes influence on the flow structure. The main results of non-isothermal experimental research show that there are three specific zones in turbulent flow structure: wall area, maximal turbulent structure transformation and flow core. The analysis of non-isothermal conditions influence on turbulent pulsations generation and development mechanisms is presented. The results show significant distinction in turbulent flow spectra between isothermal and non-isothermal conditions. The present paper describes a method of experimental research, methodology of data processing and non-isothermal turbulent flow spectra results.
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Hayashi, M., T. Watanabe et K. Nagata. « The relation between shearing motions and the turbulent/non-turbulent interface in a turbulent planar jet ». Physics of Fluids 33, no 5 (mai 2021) : 055126. http://dx.doi.org/10.1063/5.0045376.

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TERASHIMA, Osamu, Yasuhiko SAKAI, Yuichi SHOUJI et Kouji NAGATA. « 0106 The Study of the Structure of Turbulent / Non-Turbulent Region in Two Dimensional Turbulent Jet ». Proceedings of the Fluids engineering conference 2010 (2010) : 17–18. http://dx.doi.org/10.1299/jsmefed.2010.17.

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Watanabe, T., Y. Sakai, K. Nagata, Y. Ito et T. Hayase. « Wavelet analysis of coherent vorticity near the turbulent/non-turbulent interface in a turbulent planar jet ». Physics of Fluids 26, no 9 (septembre 2014) : 095105. http://dx.doi.org/10.1063/1.4896298.

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Breda, M., et O. R. H. Buxton. « Behaviour of small-scale turbulence in the turbulent/non-turbulent interface region of developing turbulent jets ». Journal of Fluid Mechanics 879 (20 septembre 2019) : 187–216. http://dx.doi.org/10.1017/jfm.2019.676.

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Tomographic particle image velocimetry experiments were conducted in the near and intermediate fields of two different types of jet, one fitted with a circular orifice and another fitted with a repeating-fractal-pattern orifice. Breda & Buxton (J. Vis., vol. 21 (4), 2018, pp. 525–532; Phys. Fluids, vol. 30, 2018, 035109) showed that this fractal geometry suppressed the large-scale coherent structures present in the near field and affected the rate of entrainment of background fluid into, and subsequent development of, the fractal jet, relative to the round jet. In light of these findings we now examine the modification of the turbulent/non-turbulent interface (TNTI) and spatial evolution of the small-scale behaviour of these different jets, which are both important factors behind determining the entrainment rate. This evolution is examined in both the streamwise direction and within the TNTI itself where the fluid adapts from a non-turbulent state, initially through the direct action of viscosity and then through nonlinear inertial processes, to the state of the turbulence within the bulk of the flow over a short distance. We show that the suppression of the coherent structures in the fractal jet leads to a less contorted interface, with large-scale excursions of the inner TNTI (that between the jet’s azimuthal shear layer and the potential core) being suppressed. Further downstream, the behaviour of the TNTI is shown to be comparable for both jets. The velocity gradients develop into a canonical state with streamwise distance, manifested as the development of the classical tear-drop shaped contours of the statistical distribution of the velocity-gradient-tensor invariants $\mathit{Q}$ and $\mathit{R}$. The velocity gradients also develop spatially through the TNTI from the irrotational boundary to the bulk flow; in particular, there is a strong small-scale anisotropy in this region. This strong inhomogeneity of the velocity gradients in the TNTI region has strong consequences for the scaling of the thickness of the TNTI in these spatially developing flows since both the Taylor and Kolmogorov length scales are directly computed from the velocity gradients.
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Watanabe, Tomoaki, Carlos B. da Silva et Koji Nagata. « Non-dimensional energy dissipation rate near the turbulent/non-turbulent interfacial layer in free shear flows and shear free turbulence ». Journal of Fluid Mechanics 875 (18 juillet 2019) : 321–44. http://dx.doi.org/10.1017/jfm.2019.462.

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The non-dimensional dissipation rate $C_{\unicode[STIX]{x1D700}}=\unicode[STIX]{x1D700}L/u^{\prime 3}$, where $\unicode[STIX]{x1D700}$, $L$ and $u^{\prime }$ are the viscous energy dissipation rate, integral length scale of turbulence and root-mean-square of the velocity fluctuations, respectively, is computed and analysed within the turbulent/non-turbulent interfacial (TNTI) layer using direct numerical simulations of a planar jet, mixing layer and shear free turbulence. The TNTI layer that separates the turbulent and non-turbulent regions exists at the edge of free shear turbulent flows and turbulent boundary layers, and comprises both the viscous superlayer and turbulent sublayer regions. The computation of $C_{\unicode[STIX]{x1D700}}$ is made possible by the introduction of an original procedure, based on local volume averages within spheres of radius $r$, combined with conditional sampling as a function of the location with respect to the TNTI layer. The new procedure allows for a detailed investigation of the scale dependence of several turbulent quantities near the TNTI layer. An important achievement of this procedure consists in permitting the computation of the turbulent integral scale within the TNTI layer, which is shown to be approximately constant. Both the non-dimensional dissipation rate and turbulent Reynolds number $Re_{\unicode[STIX]{x1D706}}$ vary in space within the TNTI layer, where two relations are observed: $C_{\unicode[STIX]{x1D700}}\sim Re_{\unicode[STIX]{x1D706}}^{-1}$ and $C_{\unicode[STIX]{x1D700}}\sim Re_{\unicode[STIX]{x1D706}}^{-2}$. Specifically, whereas the viscous superlayer and part of the turbulent sublayer display $C_{\unicode[STIX]{x1D700}}\sim Re_{\unicode[STIX]{x1D706}}^{-2}$, the remaining of the turbulent sublayer exhibits $C_{\unicode[STIX]{x1D700}}\sim Re_{\unicode[STIX]{x1D706}}^{-1}$, which is consistent with non-equilibrium turbulence (Vassilicos, Annu. Rev. Fluid Mech. vol. 47, 2015, pp. 95–114).
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Breard, Eric C. P., Gert Lube, Jim R. Jones, Josef Dufek, Shane J. Cronin, Greg A. Valentine et Anja Moebis. « Coupling of turbulent and non-turbulent flow regimes within pyroclastic density currents ». Nature Geoscience 9, no 10 (5 septembre 2016) : 767–71. http://dx.doi.org/10.1038/ngeo2794.

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35

Watanabe, Tomoaki, Carlos B. da Silva, Koji Nagata et Yasuhiko Sakai. « Geometrical aspects of turbulent/non-turbulent interfaces with and without mean shear ». Physics of Fluids 29, no 8 (août 2017) : 085105. http://dx.doi.org/10.1063/1.4996199.

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Silva, Tiago S., Marco Zecchetto et Carlos B. da Silva. « The scaling of the turbulent/non-turbulent interface at high Reynolds numbers ». Journal of Fluid Mechanics 843 (21 mars 2018) : 156–79. http://dx.doi.org/10.1017/jfm.2018.143.

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The scaling of the turbulent/non-turbulent interface (TNTI) at high Reynolds numbers is investigated by using direct numerical simulations (DNS) of temporal turbulent planar jets (PJET) and shear free turbulence (SFT), with Reynolds numbers in the range $142\leqslant Re_{\unicode[STIX]{x1D706}}\leqslant 400$. For $Re_{\unicode[STIX]{x1D706}}\gtrsim 200$ the thickness of the TNTI ($\unicode[STIX]{x1D6FF}_{\unicode[STIX]{x1D714}}$), like that of its two sublayers – the viscous superlayer (VSL, $\unicode[STIX]{x1D6FF}_{\unicode[STIX]{x1D708}}$) and the turbulent sublayer (TSL, $\unicode[STIX]{x1D6FF}_{\unicode[STIX]{x1D70E}}$) – all scale with the Kolmogorov micro-scale $\unicode[STIX]{x1D702}$, while the particular scaling constant depends on the sublayer. Specifically, for $Re_{\unicode[STIX]{x1D706}}\gtrsim 200$ while the VSL is always of the order of $\unicode[STIX]{x1D702}$, with $4\leqslant \langle \unicode[STIX]{x1D6FF}_{\unicode[STIX]{x1D708}}\rangle /\unicode[STIX]{x1D702}\leqslant 5$, the TSL and the TNTI are typically equal to $10\unicode[STIX]{x1D702}$, with $10.4\leqslant \langle \unicode[STIX]{x1D6FF}_{\unicode[STIX]{x1D70E}}\rangle /\unicode[STIX]{x1D702}\leqslant 12.5$, and $15.4\leqslant \langle \unicode[STIX]{x1D6FF}_{\unicode[STIX]{x1D714}}\rangle /\unicode[STIX]{x1D702}\leqslant 16.8$, respectively.
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Gampert, Markus, Venkat Narayanaswamy, Philip Schaefer et Norbert Peters. « Conditional statistics of the turbulent/non-turbulent interface in a jet flow ». Journal of Fluid Mechanics 731 (29 août 2013) : 615–38. http://dx.doi.org/10.1017/jfm.2013.327.

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AbstractUsing two-dimensional high-speed measurements of the mixture fraction $Z$ in a turbulent round jet with nozzle-based Reynolds numbers $R{e}_{0} $ between 3000 and 18 440, we investigate the scalar turbulent/non-turbulent (T/NT) interface of the flow. The mixture fraction steeply changes from $Z= 0$ to a final value which is typically larger than 0.1. Since combustion occurs in the vicinity of the stoichiometric mixture fraction, which is around $Z= 0. 06$ for typical fuel/air mixtures, it is expected to take place largely within the turbulent/non-turbulent interface. Therefore, deep understanding of this part of the flow is essential for an accurate modelling of turbulent non-premixed combustion. To this end, we use a composite model developed by Effelsberg & Peters (Combust. Flame, vol. 50, 1983, pp. 351–360) for the probability density function (p.d.f.) $P(Z)$ which takes into account the different contributions from the fully turbulent as well as the turbulent/non-turbulent interface part of the flow. A very good agreement between the measurements and the model is observed over a wide range of axial and radial locations as well as at varying intermittency factor $\gamma $ and shear. Furthermore, we observe a constant mean mixture fraction value in the fully turbulent region. The p.d.f. of this region is thus of non-marching character, which is attributed physically to the meandering nature of the fully turbulent core of the jet flow. Finally, the location and in particular the scaling of the thickness $\delta $ of the scalar turbulent/non-turbulent interface are investigated. We provide the first experimental results for the thickness of the interface over the above-mentioned Reynolds number range and observe $\delta / L\sim R{ e}_{\lambda }^{- 1} $, where $L$ is an integral length scale and $R{e}_{\lambda } $ the local Reynolds number based on the Taylor scale $\lambda $, meaning that $\delta \sim \lambda $. This result also supports the assumption often made in modelling of the stoichiometric scalar dissipation rate ${\chi }_{st} $ being a Reynolds-number-independent quantity.
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TERASHIMA, Osamu, Yasuhiko SAKAI, Kouji NAGATA, Yuichi SHOUJI et Kazuhiro ONISHI. « Study on the Interfacial Layer between the Turbulent/Non-Turbulent Region in a Two-Dimensional Turbulent Jet ». TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B 78, no 790 (2012) : 1235–47. http://dx.doi.org/10.1299/kikaib.78.1235.

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39

Watanabe, T., Y. Sakai, K. Nagata, Y. Ito et T. Hayase. « Enstrophy and passive scalar transport near the turbulent/non-turbulent interface in a turbulent planar jet flow ». Physics of Fluids 26, no 10 (octobre 2014) : 105103. http://dx.doi.org/10.1063/1.4898208.

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Terashima, Osamu, Yasuhiko Sakai, Kouji Nagata, Yasumasa Ito, Kazuhiro Onishi et Yuichi Shouji. « Simultaneous measurement of velocity and pressure near the turbulent/non-turbulent interface of a planar turbulent jet ». Experimental Thermal and Fluid Science 75 (juillet 2016) : 137–46. http://dx.doi.org/10.1016/j.expthermflusci.2016.02.007.

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41

Nielsen, M., G. C. Larsen et K. S. Hansen. « Simulation of inhomogeneous, non-stationary and non-Gaussian turbulent winds ». Journal of Physics : Conference Series 75 (1 juillet 2007) : 012060. http://dx.doi.org/10.1088/1742-6596/75/1/012060.

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42

Dairay, T., M. Obligado et J. C. Vassilicos. « Non-equilibrium scaling laws in axisymmetric turbulent wakes ». Journal of Fluid Mechanics 781 (16 septembre 2015) : 166–95. http://dx.doi.org/10.1017/jfm.2015.493.

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We present a combined direct numerical simulation and hot-wire anemometry study of an axisymmetric turbulent wake. The data lead to a revised theory of axisymmetric turbulent wakes which relies on the mean streamwise momentum and turbulent kinetic energy equations, self-similarity of the mean flow, turbulent kinetic energy, Reynolds shear stress and turbulent dissipation profiles, non-equilibrium dissipation scalings and an assumption of constant anisotropy. This theory is supported by the present data up to a distance of 100 times the wake generator’s size, which is as far as these data extend.
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Devenport, William J., et K. Todd Lowe. « Equilibrium and non-equilibrium turbulent boundary layers ». Progress in Aerospace Sciences 131 (mai 2022) : 100807. http://dx.doi.org/10.1016/j.paerosci.2022.100807.

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Bendre, Abhijit B., et Kandaswamy Subramanian. « Non-locality of the turbulent electromotive force ». Monthly Notices of the Royal Astronomical Society 511, no 3 (10 février 2022) : 4454–63. http://dx.doi.org/10.1093/mnras/stac339.

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ABSTRACT The generation of large-scale magnetic fields ($\overline{\boldsymbol {B}}$) in astrophysical systems is driven by the mean turbulent electromotive force ($\overline{\rm{\boldsymbol {\cal E}} {}}$), the cross-correlation between local fluctuations of velocity and magnetic fields. This can depend non-locally on $\overline{\boldsymbol {B}}$ through a convolution kernel Kij. In a new approach to find Kij, we directly fit the time-series data of $\overline{\rm{\boldsymbol {\cal E}} {}}$ versus $\overline{\boldsymbol {B}}$ from a galactic dynamo simulation using singular value decomposition. We calculate the usual turbulent transport coefficients as moments of Kij, and show the importance of including non-locality over eddy length-scales to fully capture their amplitudes and that higher order corrections to the standard transport coefficients are small in this case.
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Zhukov, Dmitry, Sergey Lyamin et Natalia Barabash. « Non-Linear Effects of Turbulent Institutional Modernization ». Jahrbücher für Geschichte Osteuropas 65, no 4 (2017) : 624–50. http://dx.doi.org/10.25162/jgo-2017-0023.

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Klein, Sikke A., et Jim B. W. Kok. « Noise in non‐premixed turbulent syngas flames ». Journal of the Acoustical Society of America 103, no 5 (mai 1998) : 3045. http://dx.doi.org/10.1121/1.422619.

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47

Yu Demianov, A., A. N. Doludenko, N. A. Inogamov et E. E. Son. « The turbulent mixing of non-Newtonian fluids ». Physica Scripta T155 (1 juillet 2013) : 014019. http://dx.doi.org/10.1088/0031-8949/2013/t155/014019.

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48

CARLOTTI, PIERRE, et GARY R. HUNT. « Analytical solutions for turbulent non-Boussinesq plumes ». Journal of Fluid Mechanics 538, no -1 (17 août 2005) : 343. http://dx.doi.org/10.1017/s0022112005005379.

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Vaux, Samuel, Rabah Mehaddi, Olivier Vauquelin et Fabien Candelier. « Upward versus downward non-Boussinesq turbulent fountains ». Journal of Fluid Mechanics 867 (21 mars 2019) : 374–91. http://dx.doi.org/10.1017/jfm.2019.149.

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Turbulent miscible fountains discharged vertically from a round source into quiescent uniform unbounded environments of density $\unicode[STIX]{x1D70C}_{0}$ are investigated numerically using large-eddy simulations. Both upward and downward fountains are considered. The numerical simulations cover a wide range of the density ratio $\unicode[STIX]{x1D70C}_{i}/\unicode[STIX]{x1D70C}_{0}$, where $\unicode[STIX]{x1D70C}_{i}$ is the source density of the released fluid. These simulations are used to evaluate how the initial maximum height $H_{i}$ and the steady state height $H_{ss}$ of the fountains are affected by large density contrasts, i.e. in the general non-Boussinesq case. For both upward and downward non-Boussinesq fountains, the ratio $\unicode[STIX]{x1D706}=H_{i}/H_{ss}$ remains close to $1.45$, as usually observed for Boussinesq fountains. However the Froude (linear) scaling originally introduced by Turner (J. Fluid Mech., vol. 26 (4), 1966, pp. 779–792) for Boussinesq fountains is no longer valid to determine the steady fountain height. The ratio between $H_{ss}$ and the height predicted by the Turner’s relation turns out to be proportional to $(\unicode[STIX]{x1D70C}_{i}/\unicode[STIX]{x1D70C}_{0})^{n}$. Remarkably, it is found that the power exponent $n$ differs following the direction in which the buoyant fluid is released ($n=1/2$ for downward fountains and $n=3/4$ for upward fountains). This new result demonstrates that for non-Boussinesq turbulent fountains the configurations heavy/light and light/heavy are not equivalent. Finally, scalings are proposed for fountains, regardless of the direction (upwards and downwards) and of the density difference (Boussinesq and non-Boussinesq).
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KLEIN, S. A., et J. B. W. KOK. « Sound Generation by Turbulent Non-premixed Flames ». Combustion Science and Technology 149, no 1-6 (décembre 1999) : 267–95. http://dx.doi.org/10.1080/00102209908952109.

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