As far as I know, there is actually no difference between a vortex and an eddy. However, the words are used in different contexts:

In turbulence you usually speak of eddies and these eddies decay to smaller eddies and so forth which forms a turbulent cascade. This has nothing to do with the type of fluid. Eddies are formed in fluids, gas and plasma.

Vortices on the other hand are more stable structures and the description of their physics (e.g. geostrophic winds) do not necessarily include turbulence, i.e. you don't expext them to decay and form a turbulent cascade.

To make a flow turbulent, you need to inject energy into it. If you have a laminar flow without an obstacle and without friction, there are no forces acting on the fluid. You could Galileo-transform into the moving fluid frame and see that there's nothing happening. Therefore, you don't generate eddies and you don't have turbulence.

If you place an obstacle in the flow, it is equivalent to an injection of energy on a scale comparable to the size of the obstacle. Behind the obstacle you will see that eddies are formed. These eddies will then in turn decay to smaller and smaller eddies, i.e. you have a turbulent cascade.

As far as I know, there is actually no difference between a vortex and an eddy. However, the words are used in different contexts:

In turbulence you usually speak of eddies and these eddies decay to smaller eddies and so forth which forms a turbulent cascade. This has nothing to do with the type of fluid. Eddies are formed in fluids, gas and plasma.

Vortices on the other hand are more stable structures and the description of their physics (e.g. geostrophic winds) do not necessarily include turbulence, i.e. you don't expext them to decay and form a turbulent cascade.

To make a flow turbulent, you need to inject energy into it. If you have a laminar flow without an obstacle and without friction, there are no forces acting on the fluid. You could Galileo-transform into the moving fluid frame and see that there's nothing happening. Therefore, you don't generate eddies and you don't have turbulence.

If you place an obstacle in the flow, it is equivalent to an injection of energy on a scale comparable to the size of the obstacle. Behind the obstacle you will see that eddies are formed. These eddies will then in turn decay to smaller and smaller eddies, i.e. you have a turbulent cascade.

Hi, there are eddies and meddies and vortices. I agree with Michael that there is actually no essential difference between eddies and vortices. Vortex is used when you look at the individual case and eddy is used primarily in plural. Note that also eddies might be looked at as individuals, e.g. large eddies; one version is meddies which are complex flow structures far below the surface of the ocean. You may google them.

Maybe that an eddy is a simple 3D objekt of limited size and the vortex notion is typically domionated by vortex filmaments which have no begin and no end.

Another point. There is a new theory which makes use of the Euler and Fokker-Planck equation applied to vortex dipoles as quasi-solid particles. For the first time it gives us a value of van-Karman constant as 1/sqrt(2 pi) ~ 0.399. Not too far from standard value 0.4. No phenomenology at all. The theory is still available for free, see

http://iopscience.iop.org/1402-4896/2013/T155/014001

Regards,

Helmut

Welcome to true chaos! Fluid Mechanics has the feature does not have a clear and unambiguous notation. Michael's explanation is perfect, however there is no such certainty in all textbooks, and often the authors for literary style over and over alternate name as synonymous!!

Therefore, I suggest you follow the recommendations of Michael, but always suspecting of the text.

Now, anyone studying turbulence should already be prepared from the beginning to the non-determinism!

Hi all,

there are mesoscale eddies (meddies) who are sometimes called blini (pancakes) which are not necessarily connected with turbulence. They are large-scale features in the Central Atlantic/Mediterranean Outflow. You meet similar things when you fly through an 'air hole' which is nothing than an overturn of an internal wave and weakly turbulent for a longer time. John Woods says that the (deep enough) ocean is basically laminar but punctuated by internal-wave overturns. These are localized features.

There is no problem with different names for seemingly one and the same natural phenomenon. Fluid dynamics is no exception. (I try to avoid the word 'fluid mechanics' because of its reductionistic tendency.) We do that for plants and animals. Language is rich, nature is often richer. E.g. we talk about 'wave turbulence' if a medium is stratified and we may talk about 'fossil turbulence' (Carl Gibson) when turbulence has ceased but scalar signatures are still detectable.

In a theory you need to reduce the generally infinite complexity of nature down to a finite number of phenomena and 'participants' (either particles or waves, or both) - doing a finite number of interactions. That's what I did with turbulence, see

http://iopscience.iop.org/1402-4896/2013/T155/014001

This is similar to early stages of Newtonian celestial mechanics when celestial bodies were taken as point masses of size zero, with finite masses, without tidal friction in oceans and atmospheres etc.

In low-temperature quantum turbulence I feel that we should avoid the name 'eddy' and use exclusively 'vortex' or better 'vortex lines'.

HZB

@all.

Thanks for your valuable inputs especially Micheal and Helmut.@ Helmut, the concept of meddies is little heavy in me as of now as I just a beginner in turbulence.

But I have encountered another confusion. How do eddies and wakes differ. :-o

Hi Deewakar, 'eddy' is more or less an all-purpose notion. But 'wake' is clearly somethink very local, flow structure behind an obstacle. Maybe a von-Karman street, maybe fully turbulent or fully laminar. Form depends on the form of the obstacle.

Have a nice day,

Helmut

As Helmut and Michael have pointed out, the definition or more precisely the identification for an eddy/vortex is not as simple as one might think and can lead to confusion, especially in the area of turbulent flow. I would suggest the paper by Jeong and Hussain "On the identification of a vortex", J Fluid Mechanics, 285, p69-94 (1995) as a good start for learning the subtleties of vortex flow, and the relation to coherent structures (CS).

Even in laminar flows there can be confusion in the terminology, especially in time dependent flows. For example, the appellation gyre, is often associated with geotropic flows in the ocean resulting from circular wind driven ocean currents. The South Atlantic gyre, which flows counter clockwise, is comprised of the south Atlantic current,Benguela current, south Equatorial current, and the Brazil current. As mentioned by Helmult there is also the von Karman vortex street, that describes the separated flow behind a bluff body.

In the case of steady laminar flows the situation is a lot clearer. Take for example a steady 2-D laminar flow. In this case an eddy is essentially a recirculation zone consisting of closed streamlines ( a line that is everywhere tangent to the velocity vector), and each vortex line (a line that is everywhere tangent to the vorticity vector) is perpendicular to the flow plane. A surface that is everywhere tangent to both velocity and vorticity is called a vortex tube. In general, vortex tubes are nested around the axis of rotation.

In my area of research (coating flows), recirculation zones are undesirable, as fluid elements inside a recirculation zone can "age" resulting in coating non-uniformities when the fluid is eventually expelled from the recirculation zone (due to flow instabilities and edge effects). Thus being able to predict the birth/death of a recirculation zone in a 2-D flow is a challenging area of research. See for example, my publications on "Flow Separation at a Free Surface", and also "Study of flow in the upstream bank of a forward roll coater by the finite element method".

Maybe my first response was not clear because I spoke more of uncertainties of the  words than of certainties.

The definitions are all present here, to differentiate vortex and eddy are corrects, including the Michael that approaches our first paragraph of my answer.

The main problem is notation depending on the text (text turbulence and others) the eddy and vortex words are used as synonyms or not.

It is extremely difficult to say without knowing the context which meaning the author proposed.

It is possible to roughly differentiate in most texts as a coherent vortex structure, while eddies not keeping this feature.

If we adopt this division, the observations of Michael, "Vortices on the other hand are more stable structures and the description of Their physics ..." Theodore "The flow of real fluids have formation of vortices like the von Karman's vorticies after an obstacle." Helmut "... there are mesoscale eddies (meddies) who are sometimes called blini (pancakes) Which are not Necessarily connected with turbulence." and Brian (various sections), would be covered in part by the division of structural coherence.

It is clear the various interpretations that are structures that represent a rotation (rotational or irrotational) flow in a pre-defined and deterministic (coherent) that could be called vortices. On the other hand, there are structures that are characteristic of turbulent flow, rotational and strongly dissipative, not coherent, which could be called eddies.

Now nothing prevents either author use the terms interchangeably! What do we do? My old teacher, the late Professor. Hunter Rouse, said the following: The world would be happier if each teacher to write his books.

vortex is nothing but its a kind of motion of fluid which involves vorticity. Means the fluid elements rotate about its center or COG. There is an angular velocity vector that is associated with that fluid element. for example the boundary layer flows are highly rotational. Each fluid element continuously keep rotating and deforming too because of shear stress.

okay now let us consider a turbulent flow in which the separation is taking place.

Due to separation, the flow downstream produces what we call eddies. i means the fluid elements are already having the vorticity but in addition these fluid elements are circulating locally downstream of the separation point. So these eddies are nothing but circulation or spinning of fluid elements in circles (not exactly circles).

- jason.bourne jason

Read more: http://www.physicsforums.com

@Prof Brian

I would like to seek some clarification reg. 2D eddies in laminar flow. A fluid element rotating about its own axis as well some virtual axis may b called as a rotational fluid and hence has vorticity.

I suppose you meant that in such a case we define vortex tube and so on.

Now coming to eddies, which as per discussion so far, I have come to describe them as rotating fluid elements, I can understand them in turbulent flow when we have fluctuations but in a laminar flow, is the following example correct in this context:

Consider a beaker which is rotating about some axis. In this case I suppose it is clear to assume that fluids element are rotating about their own as well about come other axis. Hence at low rotational speed, will it be correct to say these are eddies.?? By the definition and discussion which a has gone so far into this topic, I hope I am correct in interpretation but this very example is somewhat hard to digest.

If you (or someone) may kindly elaborate on this.

Let us take your beaker example. Place a beaker partially filled on a table. The fluid is at rest. Now set the table in steady rotation about an axis perpendicular to the table surface (using a very high acceleration ramp). The fluid in the beaker is initially at rest, but because of the no-slip boundary condition at the beaker wall, the tangential fluid velocity at the beaker wall is V=omega*R, where R is the radius of the beaker an omega is the angular velocity of the table. Immediately vorticity is generated at the surface of the beaker and this vorticity diffuses into the interior of the fluid setting it into motion. This is called the spin-up problem. Eventually ( barring no fluid instabilities) all the fluid in the beaker ultimately reaches solid body rotation and the fluid is said to be in gyrostatic equilibrium- the fluid is in solid body rotation as there are no longer velocity gradients ( hence no vorticity gradients and the vorticity =2*omega). Such a flow has no eddies ( i.e., recirculation zones). Of course if the beaker is not perfectly centered on the rotating table, then instabilities can set up leading to eddies.

Note during the spin-up process (before gyro static equilibrium is reached), the fluid particle path lines are circular and the bulk of the fluid would have vorticity, but there would be no recirculation zones. But strange things may happen if there are some imperfections in the beaker geometry,. e.g. Taylor columns, or if there are temperature/ density gradients in the fluid which can give rise to Rosby waves/vortices.

The Wikipedia articles (see below) on Vortex and Eddy seem to be pretty good basic descriptions. If any of you experts in fluid dynamics (I am not one) think they are inaccurate, please consider logging in and editing them as appropriate.

https://en.wikipedia.org/wiki/Vortex

https://en.wikipedia.org/wiki/Eddy_(fluid_dynamics)

Wikipedia itself accepts that the eddy chapter is incomplete. Also, please do not try to translate industrial fluid mechanics through Oceanography, since they are different. So, everyone who wants to understand the nature of the eddies should take courses in Turbulence and Stochastic Processes in a University.

Mr. Costopoulos: The person who posed the question is clearly a beginning scientist (RG score 4.02). He asked a beginner's question, and even asked whether the definition of the terms vortex and eddy had to anything to do with whether the fluid considered was a liquid or a gas. Also, I can find no indication in his comments that he is interested in oceanography. The articles in Wikipedia on vortex and eddy are a good place for a beginner to start. If you feel they need fixing, then do beginners (and general readers) a favor and fix them. Putting on your high hat and saying the only thing to do is "take courses in Turbulence and Stochastic Processes in a University" may not be a choice for the person who posed the question. Maybe you should take a University course in diplomacy.

In my view we can close the debate by summarizing that the word "eddy" is often used synonymously for "turbulence" or "turbulent" and, sometimes, for vortex. If we want to get it more precisely, we need to introduce equations and strict abstract definitions. Maybe it pays, I don't know.

Regarding differences between industrial and geophysical fluid dynamics: there is actually only one fluid dynamics and geophysical conditions are specific only in so far as (a) rotation of the planet Earth, (b) extra-terrestrial forces from the solar system (tides), and (c) the contact zone between the ocean and the atmosphere play specific and partially dominating roles.

Yes, I agree. But sometimes complex things become simple without advanced studies, e.g. the epicycles of Ptolemaios explained by Copernicus, Kepler, Newton - here only the point of view matters; the geocentric view is "complex" but the heliocentic is simple. Maybe turbulence is a similar case: as long as you deal with Navier-Stokes you are lost, but if you treat the vortex tubes as particles in a frictionless (Eulerian) fluid you may find interesting results.

Mr. Costopoulos wrote: "We have to be honest. There are things that are easily explained with a paragraph whereas others, like turbulence, that need advanced studies."

So let's indeed be honest. Any subject (turbulence, democracy, lasers, parthenogenesis) can be explained at an elementary level in a paragraph--or even a sentence. A subject can also be explained and understood at increasingly advanced levels. The elementary dictionary definition of turbulence--"violent or unsteady movement of air, water or some other fluid"--is NOT incorrect. It is just elementary. Not everyone needs to know a subject at a level that requires advanced study. A good teacher or a good scientist fits his explanation to the level of sophistication and need of his audience.

@Prof. Daniels:

I agree with "violent or unsteady movement of ... fluid" and would like to complete this definition by adding the property "stochastic". This is a well-defined term in the theory of stochastic processes. The public likes the word "chaotic" instead but it does not guarantee a certain mixing behaviour.

@Helmut Baumert:

The elementary definition I supplied was from the virtual dictionary that came free with my Apple iMac computer.

I think your "stochastic" is a great word and could be substituted for "unsteady". Lots of people looking up turbulence in a dictionary might not know "stochastic", but it does not hurt to make the general reader work a little.

I find Wiktionary to be quite good free English dictionary on the internet. It probably has the most words and is free of advertisement boxes, etc. I don't know if the German version is a good. Wiktionary supplies 4 definitions for the noun "turbulence". The closes to our discussion is number 2:

"Disturbance in a gas or fluid, characterized by evidence of internal motion or unrest." https://en.wiktionary.org/wiki/turbulence

Again, "stochastic" might be inserted before "internal" sharpen up the definition.

Funny enough, I found I liked the Apple definition of "stochastic" better than the Wiktionalry one. Here is Apple's effort:

"randomly determined; having a random probability distribution or pattern that may be analyzed statistically but may not be predicted precisely."

Early in the Chapter XXII of the book "Parenga und Paripolemena" the nineteenth-century German philosopher, Arthur Schopenhauer, this chapter titled "On Thinking for Oneself" Schopenhauer begins his text by: "The library may be very large, but if it is in disorder, it is not so useful as one that is small but well arranged. In The Same way, a man may have a great mass of knowledge, but if he has not worked it up by thinking it over for himself, it has much less value than a far smaller amount Which he has thoroughly pondered ... "(English translation by T. Bailey Saunders).

.

This text reflects a great deal of the questions that are asked in ReseachGate, including this "What is the difference between a vortex and an eddy?".

.

We may call what Schopenhauer written as "The dilemma of Schopenhauer," because the "virtual library" grow and also the “disorder”.

.

Thirty years ago, when it had a doubt in Fluid Mechanics, for example, looking up the solution in books like "Hydrodynamics" Sir Horace Lamb, or "Boundary Layer Theory" Hermann Schilichiting or any of the books of Professor Hunter Rouse . Perhaps the solution of the problem were not in these books, but the notation and the position of the problem was.

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Organizations try to replace these books by virtual encyclopedias such as Wikipedia or other, however these attempts have two problems, the lack of a common notation and the principal and talked little, the absence of scientific authority.

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In each issue have millions of doctors ferociously disputing the primacy of knowledge. The broader, the larger the number of specialties that use the same definition and how much controversial the subject is, the more there is the fight for editing and imposition of "truth."

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You put the "dilemma", it is up to someone else to solve it.

@Rogerio Maestri:

You wrote: "Organizations try to replace these books by virtual encyclopedias such as Wikipedia or other, however these attempts have two problems, the lack of a common notation and the principal and talked little, the absence of scientific authority."

I think you misunderstand the nature of Wikipedia articles in science and engineering. They are voluntarily written by experts in their fields and then actively edited by other experts in an effort to keep them correct and up to date. For example, please take a look (see link below) at the current article on Fluid Dynamics, including its links to related articles about various aspects of the field. Also take a look at the current history (see below) of the article. You will see it has been edited 14 times since 5 June 2013. The article is viewed ca. 1000 times per day (see below). This likely makes it the single most-used reference in the field.

https://en.wikipedia.org/wiki/Fluid_dynamics

https://en.wikipedia.org/w/index.php?title=Fluid_dynamics&action=history

http://stats.grok.se/en/latest/Fluid_dynamics

The process of getting a major scientific article up on Wikipedia is rigorous. I know from personal experience. Last year I wrote and had one accepted. Others and I are still trying to improve it. https://en.wikipedia.org/wiki/Isothermal_microcalorimetry

@Prof. Daniels:

First of all: I fully agree with you in all points. Namely the terminus "stochastic", which I proposed recently as a property of turbulence, should be replaced by your "random" because this word allows for a better intuitive understanding.

Now the contents of the wiki on fluid dynamics and therein on turbulence. Here I see under the headline "Laminar vs turbulent" some problematic statements. E.g. "It is believed that turbulent flows can be described well through the use of the Navier–Stokes equations." Those believers are not too happy as in the transition to infinitely high Reynolds numbers (wiki cites airbus wings with Re ~ 40 mio) Navier-Stokes (NS) changes its equation type from parabolic to hyperbolic, with qualitatively different sets of boundaries conditions. Therefore NS are called (by professional mathematicians like Feireisl and others) "singularly perturbed" because the parabolic part is proportional to the inverse of Re and thus small. All attempts to seek a meaningful limit by series expansions of NS failed so far, and so did attempts to solve No. 3 of the CMI Millenium Problems. The methodical situation reminds of the transition from geocentrism to heliocentrism: one simply needs to avoid NS and start with pure Euler when formulating the theory of turbulence. That's exaclty what I did when starting with Euler to get more or less automatically new results, e.g. the von-Karman constant as 1/sqrt(2*pi) ~0.399 ... (the international standard value is 0.4, based on numerous experiments).

If I could find the time I would be happy to join the crew who manages the wiki on Fluid_dynamics, but at least until April 2015 I am fully occupied. But if you could

give me a hint how to contact the authors of the sentences I mentioned above, then I would try to get in touch with them.

@Helmut Baumert: You wrote

"If I could find the time I would be happy to join the crew who manages the wiki on Fluid_dynamics, but at least until April 2015 I am fully occupied. But if you could

give me a hint how to contact the authors of the sentences I mentioned above, then I would try to get in touch with them."

NO NEED TO GET IN TOUCH. NOBODY MANAGES ANY SPECIFIC ARTICLE on Wikipedia. ANYBODY can edit ANY PART of ANY article. To use the current jargon, Wikipedia is "crowd sourced" and it works beautifully. I am not joking. The "attractor principle" in action.

https://en.wikipedia.org/wiki/Attractor

WHY IT WORKS: Only people who care about a subject and know enough about it are likely to visit an article and edit it.

To verify what I say, just go to any section (after the introduction) of any article and click on the word [edit].

For example, go look at:

https://en.wikipedia.org/wiki/Fluid_dynamics#Newtonian_vs_non-Newtonian_fluids

and click on [edit]

If you make an inappropriate edit, some interested person will see it and fix it--usually quite soon. If you do something really reprehensible (add some vulgarities) there are some "BOTs" that look for such stuff, and there is a small cadre of overseers who generally "mind the store" (Wikipedia). If someone becomes a troublemaker (repeatedly making a mess of one or more articles) the overseers ban him/her.

Wikipedia is a phenomenon, and in the opinion of many (including me), one of most successful products stemming from the existence of the internet. Nothing like it has ever existed before. You might want to take a look at:

https://en.wikipedia.org/wiki/Wikipedia

and https://en.wikipedia.org/wiki/Wikipedia_policy

Dear Daniels .

I'm not criticizing the effort in no time volunteer who writes on Wikipedia . I'm not criticizing nor the manner of it. What I am saying that the fragmented way that wikipedia is , it does not replace a book that has a beginning, middle and end.

Freedom of the composition of Wikipedia , is also its weakness, as the articles are widening , as we find many interfaces between them to reconcile notations , definitions make it impossible to reconcile them due to the number of people involved in each one.

See, we're discussing something simple vortex and edge definition , something that was needed a simple definition , without entering into polemics and other differences .

Another issue , the winkiedia intended to be a modern encyclopedia , known as the old Encyclopedia Britannica , but because of its structure it will never become a textbook , with introduction and developments in the subject .

In winkipédia can use their links to complement the subject , however this does not give a default line that has a good textbook .

But , back to the beginning of my text, the " paradox of Schopenhauer " (perhaps better than dilemma ) is only strengthened by wikipedia and unresolved .

@Rogerio Maestri

Wikpedia: Not sure what you mean by "winkiedia". Guess you meant Wikipedia.

Wikipedia was never intended to be "a modern...Encyclopedia Britannica."

See: https://en.wikipedia.org/wiki/Wikipedia

You will find there that Nature (journal) ran a check and found Wikipedia science articles to be generally of high quality equivalent to the best encyclopedias (and of course not so subject to becoming out of date). And of course free.

Classic Textbooks: The trouble with classic text books that have a "beginning, middle and end" is that they are soon out of date--e.g. the references cited are soon stale, and even the concepts may soon be replaced by newer ones. Static (e.g. printed) text books are on their way out. If textbooks as such continue to exist, they will be electronic ones that are updated regularly by some designated responsible person or team.

The internet has forever changed writing and publishing--especially in science and engineering. There is no going back.

Daniels , please wikipedia , wrote correctly three times and missed one, I have no reviewer !

Now say that wikipedia never tried to be an encyclopedia is not just read the first paragraph of the link you sent me .

" This article is about the Internet encyclopedia. For other uses , see Wikipedia ( disambiguation ) "

But more importantly it seems that you do not want to see the wikipedia as was any good encyclopedia of the past was intended to support problems that teach something systematically , with an aggravating factor , the wikipedia fragmented knowledge on topics not giving continuity nor a rise to issues . Use the links on the same leads to different classifications and definitions .

I'm not interested in novelty and in actuality that this form of publication takes as something the great researchers and some teachers forget is that every year are students or new collaborators that they touch , and for more than the teacher or researcher who progresses will be in the front are people who are seeing it for the first time a subject

@Rogerio Maestri

But do all fluid dynamics text books use the same notation and organize and treat fluid dynamics topics in the same way? I doubt it. If not, then when fluid dynamicists who learned from different texts get together, they are faced with the same fragmentation when they try to work together.

That is the way things are. Fragmented. Things are ever so. Here is an example from far afield for you--surgical education and practice. Does a surgeon tend to use hip joint replacement metal femoral stems that are secured in place with acrylic cement or by surface-textured press-fit? Depends on where and by whom they were educated. In some European countries, ca. 80% are cemented and in some 80% are press-fit. Here in CH it is about 50-50. We are neutral after all.

I hope you learn to be interested in novelty. Although not all things novel are good, science and communication would die without novelty. By patent office definition, inventions must be useful, novel and unobvious. And here we are communicating by trading notes electronically. Would you prefer we wrote them out long hand and mailed them?

Vortex is a region where the flow is spinning about an axis.Eddy is the swirling of a fluid,that creates a space devoid of downstream flowing fluid (like as you say behind an obstacle).In a vortex there is no void,but an area of lower pressure.In both cases there is backflow causing the fluid to rotate.

i would say it's the same thing. any unstable large-reynolds-number flow forms eddies. An obstacle can help to locally increase the reynolds number to excite kármán-type lee eddies. generally you can say you have a vortex/eddy, in an area where vorticity dominates over strain/deformation. see also okubo-weiss parameter...

just my 2 cents..

All previous scientists gave detailed discussion on the question. Shortly, in multiphase flow, vortex is an stable flow pattern (it can last for long time and is rather invulnerable - You have to apply very strong distortion [depends on scale] to break it). eddy is an unstable flow pattern which is very vulnerable to distorsions - it breaks easily,