Is There an Asymptotic Effect of Initial and Upstream Conditions on Turbulence?

2008 ◽  
Author(s):  
William K. George
Keyword(s):  
Turbulent Flows ◽  
Turbulence Modeling ◽  
Initial Conditions ◽  
Single Point ◽  
Building Blocks ◽  
Asymptotic Independence ◽  
Point Model ◽  
Turbulence Control ◽  
The Past ◽  
Decaying Turbulence

More than two decades ago the first strong experimental results appeared suggesting that turbulent flows might not be asymptotically independent of their initial (or upstream) conditions [1]. And shortly thereafter the first theoretical explanations were offered as to why we came to believe something about turbulence that might not be true [2]. It was recognized immediately that if turbulence was indeed asymptotically independent of its initial conditions, it meant that there could be no universal single point model for turbulence [2], [3], certainly consistent with experience, but not easy to accept for the turbulence community. Even now the ideas of asymptotic independence still dominate most texts and teaching of turbulence. This paper reviews the substantial additional evidence — experimental, numerical and theoretical — for the asymptotic effect of initial and upstream conditions that has accumulated over the past 20 years. Emphasis has been placed on the canonical turbulent flows (especially wakes, jets, and homogeneous decaying turbulence), which have been the traditional building blocks for our understanding. Some of the implications for the future of turbulence modeling and research, especially LES and turbulence control, are also considered.

Asymptotic Effect of Initial and Upstream Conditions on Turbulence

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
William K. George
Keyword(s):  
New York ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Large Scale ◽  
Initial Conditions ◽  
Single Point ◽  
Building Blocks ◽  
The Self ◽  
Asymptotic Independence ◽  
Small Scale

More than two decades ago the first strong experimental results appeared suggesting that turbulent flows might not be asymptotically independent of their initial (or upstream) conditions (Wygnanski et al., 1986, “On the Large-Scale Structures in Two-Dimensional Smalldeficit, Turbulent Wakes,” J. Fluid Mech., 168, pp. 31–71). And shortly thereafter the first theoretical explanations were offered as to why we came to believe something about turbulence that might not be true (George, 1989, “The Self-Preservation of Turbulent Flows and its Relation to Initial Conditions and Coherent Structures,” Advances in Turbulence, W. George and R. Arndt, eds., Hemisphere, New York, pp. 1–41). These were contrary to popular belief. It was recognized immediately that if turbulence was indeed asymptotically independent of its initial conditions, it meant that there could be no universal single point model for turbulence (George, 1989, “The Self-Preservation of Turbulent Flows and its Relation to Initial Conditions and Coherent Structures,” Advances in Turbulence, W. George and R. Arndt, eds., Hemisphere, New York, pp. 1–41; Taulbee, 1989, “Reynolds Stress Models Applied to Turbulent Jets,” Advances in Turbulence, W. George and R. Arndt, eds., Hemisphere, New York, pp. 29–73) certainly consistent with experience, but even so not easy to accept for the turbulence community. Even now the ideas of asymptotic independence still dominate most texts and teaching of turbulence. This paper reviews the substantial additional evidence - experimental, numerical and theoretical - for the asymptotic effect of initial and upstream conditions that has accumulated over the past 25 years. Also reviewed is evidence that the Kolmogorov theory for small scale turbulence is not as general as previously believed. Emphasis has been placed on the canonical turbulent flows (especially wakes, jets, and homogeneous decaying turbulence), which have been the traditional building blocks for our understanding. Some of the important outstanding issues are discussed; and implications for the future of turbulence modeling and research, especially LES and turbulence control, are also considered.

Non-Gaussian scalar statistics in homogeneous turbulence

1996 ◽  
Vol 313 ◽  
pp. 241-282 ◽  
Author(s):  
F. A. Jaberi ◽  
R. S. Miller ◽  
C. K. Madnia ◽  
P. Givi
Keyword(s):  
Turbulent Flows ◽  
Initial Conditions ◽  
Single Point ◽  
Passive Scalar ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Spatial Derivatives ◽  
Linear Eddy Model ◽  
Non Gaussian ◽  
Scalar Amplitude

Results are presented of numerical simulations of passive scalar mixing in homogeneous, incompressible turbulent flows. These results are generated via the Linear Eddy Model (LEM) and Direct Numerical Simulation (DNS) of turbulent flows under a variety of different conditions. The nature of mixing and its response to the turbulence field is examined and the single-point probability density function (p.d.f.) of the scalar amplitude and the p.d.f.s of the scalar spatial-derivatives are constructed. It is shown that both Gaussian and exponential scalar p.d.f.s emerge depending on the parameters of the simulations and the initial conditions of the scalar field. Aided by the analyses of data, several reasons are identified for the non-Gaussian behaviour of the scalar amplitude. In particular, two mechanisms are identified for causing exponential p.d.f.s: (i) a non-uniform action of advection on the large and the small scalar scales, (ii) the nonlinear interaction of the scalar and the velocity fluctuations at small scales. In the absence of a constant non-zero mean scalar gradient, the behaviour of the scalar p.d.f. is very sensitive to the initial conditions. In the presence of this gradient, an exponential p.d.f. is not sustained regardless of initial conditions. The numerical results pertaining to the small-scale intermittency (non-Gaussian scalar derivatives) are in accord with laboratory experimental results. The statistics of the scalar derivatives and those of the velocity-scalar fluctuations are also in accord with laboratory measured results.

Formation of Carbon-Oxygen Bond Mediated by Hypervalent Iodine Reagents Under Metal-free Conditions

2020 ◽  
Vol 17 ◽  
Author(s):  
Ayesha Jalil ◽  
Yaxin O Yang ◽  
Zhendong Chen ◽  
Rongxuan Jia ◽  
Tianhao Bi ◽  
...  
Keyword(s):  
Natural Products ◽  
Bond Formation ◽  
Building Blocks ◽  
Review Article ◽  
Hypervalent Iodine ◽  
Metal Free ◽  
Bioactive Natural Products ◽  
The Past ◽  
Oxygen Bond ◽  
Privileged Scaffolds

: Hypervalent iodine reagents are a class of non-metallic oxidants have been widely used in the construction of several sorts of bond formations. This surging interest in hypervalent iodine reagents is essentially due to their very useful oxidizing properties, combined with their benign environmental character and commercial availability from the past few decades ago. Furthermore, these hypervalent iodine reagents have been used in the construction of many significant building blocks and privileged scaffolds of bioactive natural products. The purpose of writing this review article is to explore all the transformations in which carbon-oxygen bond formation occurred by using hypervalent iodine reagents under metal-free conditions

Lattice Boltzmann for Turbulence Modeling

2018 ◽  
Author(s):  
Sauro Succi
Keyword(s):  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
Turbulence Modeling ◽  
Real Life ◽  
Practical Interest ◽  
Reynolds Numbers ◽  
Full Resolution ◽  
To Come ◽  
Highly Turbulent Flows ◽  
Main Ideas

This chapter introduces the main ideas behind the application of LBE methods to the problem of turbulence modeling, namely the simulation of flows which contain scales of motion too small to be resolved on present-day and foreseeable future computers. Many real-life flows of practical interest exhibit Reynolds numbers far too high to be directly simulated in full resolution on present-day computers and arguably for many years to come. This raises the challenge of predicting the behavior of highly turbulent flows without directly simulating all scales of motion which take part to turbulence dynamics, but only those that fall within the computer resolution at hand.

scholarly journals PyroMEMS as Future Technological Building Blocks for Advanced Microenergetic Systems

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 118
Author(s):  
Jean-Laurent Pouchairet ◽  
Carole Rossi
Keyword(s):  
Building Block ◽  
Building Blocks ◽  
Small Scale ◽  
Technological Evolution ◽  
Research Groups ◽  
Function Block ◽  
The Past ◽  
New Methods ◽  
Safety And Reliability ◽  
Electronically Controllable

For the past two decades, many research groups have investigated new methods for reducing the size and cost of safe and arm-fire systems, while also improving their safety and reliability, through batch processing. Simultaneously, micro- and nanotechnology advancements regarding nanothermite materials have enabled the production of a key technological building block: pyrotechnical microsystems (pyroMEMS). This building block simply consists of microscale electric initiators with a thin thermite layer as the ignition charge. This microscale to millimeter-scale addressable pyroMEMS enables the integration of intelligence into centimeter-scale pyrotechnical systems. To illustrate this technological evolution, we hereby present the development of a smart infrared (IR) electronically controllable flare consisting of three distinct components: (1) a controllable pyrotechnical ejection block comprising three independently addressable small-scale propellers, all integrated into a one-piece molded and interconnected device, (2) a terminal function block comprising a structured IR pyrotechnical loaf coupled with a microinitiation stage integrating low-energy addressable pyroMEMS, and (3) a connected, autonomous, STANAG 4187 compliant, electronic sensor arming and firing block.

Studying Palestinian-Israeli Relations at the Vanderbilt Television News Archive (VTNA)

2000 ◽  
Vol 34 (1) ◽  
pp. 38-40
Author(s):  
Deborah L. Wheeler
Keyword(s):  
Mass Media ◽  
Collective Identity ◽  
Television News ◽  
Building Blocks ◽  
Media Culture ◽  
The Past ◽  
Shared Identity ◽  
P 16 ◽  
The Creation ◽  
Words And Images

For the Past Five Decades, media texts, broadcast over television air waves, have created a shared identity among viewing audiences. John B. Thompson notes that if culture is understood as “the ways in which meaningful expressions of various kinds are produced, constructed and received by individuals”, then mass media can be understood as central to the creation and maintenance of culture (pp. 122-23). The words and images that construct a media culture are the very building blocks of collective identity. As Michael Schudson observes, “news is part of the background through which and with which people think” (p. 16).

Review of Recent Advances in the Study of Unsteady Turbulent Internal Flows

1995 ◽  
Vol 48 (4) ◽  
pp. 189-212 ◽  
Author(s):  
G. J. Brereton ◽  
R. R. Mankbadi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Modeling ◽  
Unsteady Flows ◽  
Turbulence Models ◽  
Research Area ◽  
Transition To Turbulence ◽  
Measurement Technology ◽  
Internal Flows ◽  
Recent Advances ◽  
The Many

Turbulent flow which undergoes organized temporal unsteadiness is a subject of great importance to unsteady aerodynamic and thermodynamic devices. Of the many classes of unsteady flows, those bounded by rigid smooth walls are particularly amenable to fundamental studies of unsteady turbulence and its modeling. These flows are presently being given increased attention as interest grows in the prospect of predicting non-equilibrium turbulence and because of their relevance to turbulence–acoustics interactions, in addition to their importance as unsteady flows in their own right. It is therefore timely to present a review of recent advances in this area, with particular emphasis placed on physical understanding of the turbulent processes in these flows and the development of turbulence models to predict them. A number of earlier reviews have been published on unsteady turbulent flows, which have tended to focus on specific aspects of certain flows. This review is intended to draw together, from the diverse literature on the subject, information on fundamental aspects of these flows which are relevant to improved understanding and development of predictive models. Of particular relevance are issues of instability and transition to turbulence in reciprocating flows, the robustness of coherent structures in wall-bounded flows to forced perturbations (in contrast to the relative ease of manipulation in free shear flows), unsteady scalar transport, improved measurement technology, recent contributions to target data for model testing and the quasi-steady and non-steady rapid distortion approaches to turbulence modeling in these flows. The present article aims to summarize recent contributions to this research area, with a view to consolidating comprehension of the well-known basics of these flows, and drawing attention to critical gaps in information which restrict our understanding of unsteady turbulent flows.

scholarly journals The non-equilibrium region of grid-generated decaying turbulence

2014 ◽  
Vol 744 ◽  
pp. 5-37 ◽  
Author(s):  
P. C. Valente ◽  
J. C. Vassilicos
Keyword(s):  
Turbulent Flows ◽  
Integral Scale ◽  
Dissipation Coefficient ◽  
Integral Scales ◽  
Usual Equilibrium ◽  
Decaying Turbulence ◽  
Equilibrium Region ◽  
Non Equilibrium

AbstractThe previously reported non-equilibrium dissipation law is investigated in turbulent flows generated by various regular and fractal square grids. The flows are documented in terms of various turbulent profiles which reveal their differences. In spite of significant inhomogeneity and anisotropy differences, the new non-equilibrium dissipation law is observed in all of these flows. Various transverse and longitudinal integral scales are measured and used to define the dissipation coefficient $C_{\varepsilon }$. It is found that the new non-equilibrium dissipation law is not an artefact of a particular choice of the integral scale and that the usual equilibrium dissipation law can actually coexist with the non-equilibrium law in different regions of the same flow.

Emulsion templated advanced functional materials from emerging nano building blocks

2021 ◽  
Author(s):  
Chenfei Yao ◽  
Ge Shi ◽  
Yijie Hu ◽  
Hao Zhuo ◽  
Zehong Chen ◽  
...  
Keyword(s):  
Transition Metal ◽  
Functional Materials ◽  
Building Blocks ◽  
Metal Carbides ◽  
Transition Metal Carbides ◽  
The Past ◽  
Great Progress

The development of emulsion templated functional materials has achieved great progress in the past decades in academic and industrial fields. Recently, new building blocks such as graphene, transition metal carbides...

Interior heating and outgassing of Proxima Cen b: Identification of critical parameters

2021 ◽  
Author(s):  
Lena Noack ◽  
Kristina Kislyakova ◽  
Colin Johnstone ◽  
Manuel Güdel ◽  
Luca Fossati
Keyword(s):  
Magnetic Field ◽  
Induction Heating ◽  
Initial Conditions ◽  
Thermal Evolution ◽  
Rotation Period ◽  
Critical Parameters ◽  
Stellar Spectrum ◽  
Orbital Inclination ◽  
The Past ◽  
Tidal Heating

<p>Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior.<br>We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere.</p><p><br>To study the coupled star-planet evolution, we analyse the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculate different rotation evolutionary tracks for Proxima Centauri and investigate the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely higher in the past. <br>We apply an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, i.e. different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. <br>We use a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions we chose randomly selected values. We take into account heating in the interior due to variable radioactive heat sources and latitute- and radius-dependent induction heating, and compare the heating efficiency to tidal heating.</p><p><br>Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin (see Fig. 1). This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet would not have been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. We furthermore find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior.</p><p> </p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.53bcd48f2cff56572630161/sdaolpUECMynit/12UGE&app=m&a=0&c=314fe555893c77417d52bf9a6bd3825f&ct=x&pn=gnp.elif&d=1" alt="" width="307" height="339"> </p><p>Fig 1: Local induction heating and resulting temperature variations compared to a simulation without induction heating after 1 Gyr of thermal evolution for an example rocky planet of 1.8 Earth masses with an iron content of 20 wt-%.</p>

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