The Efficiency of Turbulent Mixing in Stratified Fluids PDF Download
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Author: Guenther Wolfgang Ebert
Publisher:
ISBN:
Category :
Languages : en
Pages : 138
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Book Description
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.
Author: Guenther Wolfgang Ebert
Publisher:
ISBN:
Category :
Languages : en
Pages : 138
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Book Description
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.
Author: Young-Gyu Park
Publisher:
ISBN:
Category :
Languages : en
Pages : 126
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Book Description
A turbulent mixing experiment was conducted to observe the dynamics and the energetics of layer formation along with the region of layer formation in the Reynolds number (Re) and the overall Richardson number (Rio) space. A salt stratified fluid was mixed uniformly throughout its depth with a vertical rod that moved horizontally at a constant speed. The evolution of density was measured with a conductivity probe. As the instability theory of Phillips (1972) and Posmentier (1977) shows, an initially uniform density profile turns into a series of steps when Rio is larger than a critical value Ric, which forms a stability boundary. For fixed Re, as Rio decreases to Ric, the steps get weaker; the density difference across the interface and the difference of density gradient between layers and interfaces become small. Ric increases as Re increases with a functional relation log Ric ~ Re/900. The steps evolve over time, with small steps forming first, and larger steps appearing later through merging and decay of the interfaces. After some time the interior seems to reach an equilibrium state and the evolution of the interior steps stops. The length scale of the equilibrium step, ls, is a linear function of U /Ni, where U is the speed of the rod and Ni is the buoyancy frequency of the initial profile. The functional relationship is ls = 2.6U / Ni + l. Ocm. For Rio Ric, the mixing efficiency, Rf, monotonically decreases to the end of a run. However, for Rio Ric, the evolution of Rf is closely related to the evolution of the density field. Rf changes rapidly during the initiation of the steps. For Rio” Ric, R1 increases initially, while for Rio e"Ric, Rf ecreases initially. When the interior reaches an equilibrium state, Rf becomes uniform. Posmentier (1977) theorized that when steps reach an equilibrium state, a density flux is independent of the density gradient. The present experiments show a uniform density flux in the layered interior irrespective of the density structure, and this strongly supports the theory of Posmentier. The density flux generated in the bottom boundary mixed layer goes through the interior all the way to the top boundary mixed layer without changing the interior density structure. Thus, turbulence can transport scalar properties further than the characteristic length scale of active eddies without changing a density structure. When the fluid becomes two mixed layers, the relation between Rf and Ril was found for Ril> 1. Here, Ril is the local Richardson number based on the thickness of the interface. R, does decrease as Ril increases, which is the most crucial assumption of the instability theory.
Author: Robert Sugden Rogallo
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 98
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Book Description
Author: Men-Cheh Tao
Publisher:
ISBN:
Category : Fluid dynamics
Languages : en
Pages : 284
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Book Description
Author: Robert Brodkey
Publisher: Elsevier
ISBN: 0323154689
Category : Technology & Engineering
Languages : en
Pages : 352
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Book Description
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.
Author: Michael Meredith
Publisher: Elsevier
ISBN: 0128215135
Category : Science
Languages : en
Pages : 386
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Book Description
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
Author: Imad Awni Hannoun
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 310
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Author: M. Harindra Joseph S. Fernando
Publisher:
ISBN:
Category :
Languages : en
Pages : 232
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Author: J.C.J. Nihoul
Publisher: Elsevier
ISBN: 0080870848
Category : Science
Languages : en
Pages : 557
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Book Description
This volume contains the proceedings of the 19th International Liège Colloquium on Ocean Hydrodynamics, the programme of which focused on the relationships between small-scale mixing and large-scale features, transports and processes. The presentation of papers on various methods of parameterization of small-scale turbulent mixing for numerical ocean models was particularly encouraged and this resulted in more than a third of the papers presented at the Colloquium dealing in one way or another with the parameterization problems; many of these papers demonstrate the direct results of modelling. These proportions are well reflected in this volume of proceedings and thus emphasize once more the importance of small-scale turbulence research for such vital practical applications as ocean modelling and forecasting.
Author: S. Murthy
Publisher: Springer Science & Business Media
ISBN: 1461587387
Category : Science
Languages : en
Pages : 469
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Book Description
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.
