scholarly journals Velocity derivative skewness in fractal-generated, non-equilibrium grid turbulence

2015 ◽  
Vol 27 (7) ◽  
pp. 071701 ◽  
Author(s):  
R. J. Hearst ◽  
P. Lavoie
Keyword(s):  
Grid Turbulence ◽  
Velocity Derivative ◽  
Non Equilibrium

scholarly journals Boundedness of the velocity derivative skewness in various turbulent flows

2015 ◽  
Vol 781 ◽  
pp. 727-744 ◽  
Author(s):  
R. A. Antonia ◽  
S. L. Tang ◽  
L. Djenidi ◽  
L. Danaila
Keyword(s):  
Turbulent Flows ◽  
Nauk Sssr ◽  
Numerical Data ◽  
Universal Constant ◽  
Energy Dissipation Rate ◽  
Small Scale ◽  
Grid Turbulence ◽  
Similarity Hypothesis ◽  
Velocity Derivative ◽  
Scale Turbulence

The variation of $S$, the velocity derivative skewness, with the Taylor microscale Reynolds number $\mathit{Re}_{{\it\lambda}}$ is examined for different turbulent flows by considering the locally isotropic form of the transport equation for the mean energy dissipation rate $\overline{{\it\epsilon}}_{iso}$. In each flow, the equation can be expressed in the form $S+2G/\mathit{Re}_{{\it\lambda}}=C/\mathit{Re}_{{\it\lambda}}$, where $G$ is a non-dimensional rate of destruction of $\overline{{\it\epsilon}}_{iso}$ and $C$ is a flow-dependent constant. Since $2G/\mathit{Re}_{{\it\lambda}}$ is found to be very nearly constant for $\mathit{Re}_{{\it\lambda}}\geqslant 70$, $S$ should approach a universal constant when $\mathit{Re}_{{\it\lambda}}$ is sufficiently large, but the way this constant is approached is flow dependent. For example, the approach is slow in grid turbulence and rapid along the axis of a round jet. For all the flows considered, the approach is reasonably well supported by experimental and numerical data. The constancy of $S$ at large $\mathit{Re}_{{\it\lambda}}$ has obvious ramifications for small-scale turbulence research since it violates the modified similarity hypothesis introduced by Kolmogorov (J. Fluid Mech., vol. 13, 1962, pp. 82–85) but is consistent with the original similarity hypothesis (Kolmogorov, Dokl. Akad. Nauk SSSR, vol. 30, 1941, pp. 299–303).

Characteristics of Non-equilibrium Grid Turbulence and Scalar Transfer Mechanism

2016 ◽  
Vol 2016 (0) ◽  
pp. K05200
Author(s):  
Yasuhiko SAKAI ◽  
Koji NAGATA ◽  
Yasumasa ITO ◽  
Tomoaki WATANABE ◽  
Koji IWANO
Keyword(s):  
Transfer Mechanism ◽  
Grid Turbulence ◽  
Non Equilibrium

scholarly journals The role of velocity derivative skewness in understanding non-equilibrium turbulence

2020 ◽  
Vol 29 (11) ◽  
pp. 114702
Author(s):  
Feng Liu ◽  
Le Fang ◽  
Liang Shao
Keyword(s):  
Velocity Derivative ◽  
Non Equilibrium

Reappraisal of the velocity derivative flatness factor in various turbulent flows

2018 ◽  
Vol 847 ◽  
pp. 244-265 ◽  
Author(s):  
S. L. Tang ◽  
R. A. Antonia ◽  
L. Djenidi ◽  
L. Danaila ◽  
Y. Zhou
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Scale Effects ◽  
Nauk Sssr ◽  
Grid Turbulence ◽  
Similarity Hypothesis ◽  
Reynolds Number Effect ◽  
Pressure Diffusion ◽  
Velocity Derivative

We first analytically show, starting with the Navier–Stokes equations, that the value of the derivative flatness is controlled by pressure diffusion of energy, viscous destructive effects and large-scale effects (decay and/or production). The latter two terms tend to zero when the Taylor-microscale Reynolds number $Re_{\unicode[STIX]{x1D706}}$ is sufficiently large. We argue that the pressure-diffusion term should also tend to a constant at large $Re_{\unicode[STIX]{x1D706}}$. Available data for the velocity derivative flatness, $F$, in different turbulent flows are re-examined and interpreted in the light of the finite-Reynolds-number effect. It is found that $F$ can differ from flow to flow at moderate $Re_{\unicode[STIX]{x1D706}}$; for a given flow, $F$ may also depend on the initial conditions. The data for $F$ in various flows, e.g. along the axis in the far field of plane and circular jets, and grid turbulence, show that it approaches a constant, with a value slightly larger than 10, when $Re_{\unicode[STIX]{x1D706}}$ is sufficiently large. This behaviour for $F$ is supported, at least qualitatively, by our analytical considerations. The constancy of $F$ at large $Re_{\unicode[STIX]{x1D706}}$ violates the refined similarity hypothesis introduced by Kolmogorov (J. Fluid Mech., vol. 13, 1962, pp. 82–85) to account for the intermittency of the energy dissipation rate. It is not, however, inconsistent with Kolmogorov’s original similarity hypothesis (Dokl. Akad. Nauk SSSR, vol. 30, 1941, pp. 299–303), although we contend that the power-law relation $F\sim Re_{\unicode[STIX]{x1D706}}^{\unicode[STIX]{x1D6FC}_{4}}$ (Kolmogorov 1962), which is widely accepted in the literature, has in reality been almost invariably used to ‘model’ the finite-Reynolds-number effect for the laboratory data and has been strongly influenced by the weighting given to the atmospheric surface layer data. The inclusion of the latter data has misled previous investigations of how $F$ varies with $Re_{\unicode[STIX]{x1D706}}$.

Effects of grid geometry on non-equilibrium dissipation in grid turbulence

2017 ◽  
Vol 29 (1) ◽  
pp. 015102 ◽  
Author(s):  
Koji Nagata ◽  
Teppei Saiki ◽  
Yasuhiko Sakai ◽  
Yasumasa Ito ◽  
Koji Iwano
Keyword(s):  
Grid Turbulence ◽  
Non Equilibrium

Application of analytical electron microscopy to studies of equilibrium and non-equilibrium segregation in materials

1992 ◽  
Vol 50 (2) ◽  
pp. 1214-1215
Author(s):  
Edward A Kenik
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Extended Defects ◽  
Probe Diameter ◽  
Specimen Holder ◽  
Analytical Electron ◽  
Scanning Transmission ◽  
Solute Atoms ◽  
Equilibrium Segregation ◽  
Non Equilibrium

Segregation of solute atoms to grain boundaries, dislocations, and other extended defects can occur under thermal equilibrium or non-equilibrium conditions, such as quenching, irradiation, or precipitation. Generally, equilibrium segregation is narrow (near monolayer coverage at planar defects), whereas non-equilibrium segregation exhibits profiles of larger spatial extent, associated with diffusion of point defects or solute atoms. Analytical electron microscopy provides tools both to measure the segregation and to characterize the defect at which the segregation occurs. This is especially true of instruments that can achieve fine (<2 nm width), high current probes and as such, provide high spatial resolution analysis and characterization capability. Analysis was performed in a Philips EM400T/FEG operated in the scanning transmission mode with a probe diameter of <2 nm (FWTM). The instrument is equipped with EDAX 9100/70 energy dispersive X-ray spectrometry (EDXS) and Gatan 666 parallel detection electron energy loss spectrometry (PEELS) systems. A double-tilt, liquid-nitrogen-cooled specimen holder was employed for microanalysis in order to minimize contamination under the focussed spot.

Equilibrium and Non-Equilibrium Statistical Thermodynamics

2004 ◽  
Author(s):  
Michel Le Bellac ◽  
Fabrice Mortessagne ◽  
G. George Batrouni
Keyword(s):  
Statistical Thermodynamics ◽  
Non Equilibrium
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