Underlying Physics of Mixing Efficiency of Stably Stratified Turbulence
Underlying Physics of Mixing Efficiency of Stably Stratified Turbulence

Author: Young Ro Yi

Publisher:

Published: 2023

Total Pages: 0

ISBN-13:

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Global and regional ocean simulations rely on eddy viscosities and diffusivities to represent the unresolved turbulent mixing of momentum and scalars. The simulated flow and the transport of quantities such as heat and carbon are quite sensitive to how the turbulence is modeled. Particularly, the eddy diffusivity model of Osborn (1980) is widely used to represent the vertical buoyancy flux, which requires accurate knowledge of the mixing coefficient--defined as the ratio of the dissipation rates of available turbulent potential energy (TPE) and turbulent kinetic energy (TKE). While a constant value of 0.2 is often prescribed for the mixing coefficient, there is significant evidence for parameterizing it as a function of dimensionless numbers that characterize the state of the turbulence. Using direct numerical simulations, we studied stably stratified turbulence under three different sets of forcing: (i) linear axisymmetric forcing; (ii) three types of shear forcing; and (iii) combined momentum and buoyancy forcing. By analyzing the budgets of the normal Reynolds stresses and the vertical buoyancy flux, we observed that terms involving the pressure field (i.e., pressure-strain correlations and pressure scrambling) exhibited significant changes as the turbulent mixing became more efficient. Each of these three sets of flows exhibited quantitative physical differences in their mixing characteristics. Our findings suggested the need for improved models of the turbulent mixing in stratified flows, which we achieved by revising existing scaling relationships for the mixing coefficient and exploring anisotropic model forms for the turbulent momentum and scalar fluxes.

Mixing and Dispersion in Flows Dominated by Rotation and Buoyancy
Mixing and Dispersion in Flows Dominated by Rotation and Buoyancy

Author: Herman J.H. Clercx

Publisher: Springer

Published: 2017-10-24

Total Pages: 225

ISBN-13: 3319668870

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The book presents a state-of-the-art overview of current developments in the field in a way accessible to attendees coming from a variety of fields. Relevant examples are turbulence research, (environmental) fluid mechanics, lake hydrodynamics and atmospheric physics. Topics discussed range from the fundamentals of rotating and stratified flows, mixing and transport in stratified or rotating turbulence, transport in the atmospheric boundary layer, the dynamics of gravity and turbidity currents eventually with effects of background rotation or stratification, mixing in (stratified) lakes, and the Lagrangian approach in the analysis of transport processes in geophysical and environmental flows. The topics are discussed from fundamental, experimental and numerical points of view. Some contributions cover fundamental aspects including a number of the basic dynamical properties of rotating and or stratified (turbulent) flows, the mathematical description of these flows, some applications in the natural environment, and the Lagrangian statistical analysis of turbulent transport processes and turbulent transport of material particles (including, for example, inertial and finite-size effects). Four papers are dedicated to specific topics such as transport in (stratified) lakes, transport and mixing in the atmospheric boundary layer, mixing in stratified fluids and dynamics of turbidity currents. The book is addressed to doctoral students and postdoctoral researchers, but also to academic and industrial researchers and practicing engineers, with a background in mechanical engineering, applied physics, civil engineering, applied mathematics, meteorology, physical oceanography or physical limnology.

Ocean Mixing
Ocean Mixing

Author: Michael Meredith

Publisher: Elsevier

Published: 2021-09-16

Total Pages: 386

ISBN-13: 0128215135

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Ocean Mixing: Drivers, Mechanisms and Impacts presents a broad panorama of one of the most rapidly-developing areas of marine science. It highlights the state-of-the-art concerning knowledge of the causes of ocean mixing, and a perspective on the implications for ocean circulation, climate, biogeochemistry and the marine ecosystem. This edited volume places a particular emphasis on elucidating the key future questions relating to ocean mixing, and emerging ideas and activities to address them, including innovative technology developments and advances in methodology. Ocean Mixing is a key reference for those entering the field, and for those seeking a comprehensive overview of how the key current issues are being addressed and what the priorities for future research are. Each chapter is written by established leaders in ocean mixing research; the volume is thus suitable for those seeking specific detailed information on sub-topics, as well as those seeking a broad synopsis of current understanding. It provides useful ammunition for those pursuing funding for specific future research campaigns, by being an authoritative source concerning key scientific goals in the short, medium and long term. Additionally, the chapters contain bespoke and informative graphics that can be used in teaching and science communication to convey the complex concepts and phenomena in easily accessible ways. Presents a coherent overview of the state-of-the-art research concerning ocean mixing Provides an in-depth discussion of how ocean mixing impacts all scales of the planetary system Includes elucidation of the grand challenges in ocean mixing, and how they might be addressed

The Efficiency of Turbulent Mixing in Stratified Fluids
The Efficiency of Turbulent Mixing in Stratified Fluids

Author: Guenther Wolfgang Ebert

Publisher:

Published: 2010

Total Pages: 138

ISBN-13:

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Mixing is a common feature of stratified fluids. In stratified fluids the density varies with the height. This is true for the most fluids in geophysical environments, like lakes, the atmosphere or the ocean. Turbulent mixing plays a crucial role for the overall energy budget of the earth and has therefore an huge impact on the global climate. By introducing the mixing efficiency, it is possible to quantify mixing. It is defined as the ratio of gain of potential energy to the injection of mechanical energy. In the ocean energy provided by tidal forces leads to turbulence and thus highly dense water is lifted up from the deep sea to the surface. For this process, a mixing efficiency of 0.2 is estimated. Until now it is not completely understood how this high value can be achieved. Thus we measured the mixing efficiency by using a Couette-Taylor system, which can produce steady-state homogeneous turbulence. This is similar to what we find in the ocean. The Couette-Taylor system consists of two concentric cylinders that can be rotated independently. In between a stratified fluid is filled using salt as a stratifying agent. In the laboratory experiment, we obtained mixing efficiencies in the order of 0.001 as a result. Moreover we found that the mixing efficiency decreases with decreasing stratification like previous laboratory experiments have shown. As this value is two orders of magnitude smaller than what we find in the ocean, further studies will be necessary.

Modeling and Simulation of Turbulent Mixing and Reaction
Modeling and Simulation of Turbulent Mixing and Reaction

Author: Daniel Livescu

Publisher: Springer Nature

Published: 2020-02-19

Total Pages: 273

ISBN-13: 9811526435

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This book highlights recent research advances in the area of turbulent flows from both industry and academia for applications in the area of Aerospace and Mechanical engineering. Contributions include modeling, simulations and experiments meant for researchers, professionals and students in the area.

Turbulence in Mixing Operations
Turbulence in Mixing Operations

Author: Robert Brodkey

Publisher: Elsevier

Published: 2012-12-02

Total Pages: 352

ISBN-13: 0323154689

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Turbulence in Mixing Operations: Theory and Application to Mixing and Reaction presents a summary of the current status of research on turbulent motion, mixing, and kinetics. Each chapter of this book discusses turbulence in the context of mixing and reaction in scalar fields. Chapters I and III discuss the classification of turbulent reacting systems and the different possibilities in this context. Chapter II reviews the properties of passive mixing. Chapter IV looks at turbulent mixing in chemically reactive flows. Chapter V uses different techniques to make parallel numerical calculations of both mixing and reaction. Finally, Chapter VI reviews turbulence and actual industrial mixing operations. This book will be of great value for chemical and industrial engineers, especially for those interested in turbulent and industrial mixing.

Turbulent Mixing in Nonreactive and Reactive Flows
Turbulent Mixing in Nonreactive and Reactive Flows

Author: S. Murthy

Publisher: Springer Science & Business Media

Published: 2013-11-11

Total Pages: 469

ISBN-13: 1461587387

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Turbulence, mixing and the mutual interaction of turbulence and chemistry continue to remain perplexing and impregnable in the fron tiers of fluid mechanics. The past ten years have brought enormous advances in computers and computational techniques on the one hand and in measurements and data processing on the other. The impact of such capabilities has led to a revolution both in the understanding of the structure of turbulence as well as in the predictive methods for application in technology. The early ideas on turbulence being an array of complicated phenomena and having some form of reasonably strong coherent struc ture have become well substantiated in recent experimental work. We are still at the very beginning of understanding all of the aspects of such coherence and of the possibilities of incorporating such structure into the analytical models for even those cases where the thin shear layer approximation may be valid. Nevertheless a distinguished body of "eddy chasers" has come into existence. The structure of mixing layers which has been studied for some years in terms of correlations and spectral analysis is also getting better understood. Both probability concepts such as intermittency and conditional sampling as well as the concept of large scale structure and the associated strain seem to indicate possibilities of distinguishing and synthesizing 'engulfment' and molecular mixing.