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-   -   what is difference between recirculation region, eddy field and vortex? (http://www.cfd-online.com/Forums/main/102097-what-difference-between-recirculation-region-eddy-field-vortex.html)

fruitkiwi May 22, 2012 07:26

what is difference between recirculation region, eddy field and vortex?
 
Hi, Dear all,

Inspired by CFD unlimited descriptive term, i get lost.

As tittle stated, the definition of recirculation region means the a stationary vortex, where the vortex does not move, it will become recirculation region.

A moving vortex is a vortex, a stationary vortex is a recirculation region, am i right?

Then comes to eddy, I always though eddy is vortex.then a stationary eddy is a recirculation region.

"Particles in the recirculation region, aways from the separatrix, are affected by the eddy field more intensely" a sentence from journal.

so what is difference between recirculation region, eddy field and vortex?

fruitkiwi May 22, 2012 20:55

I am serious with this question, can anyone help?

mettler May 23, 2012 08:27

to the best of my knowledge, a recirculation zone does not move, an eddy moves. A recirculation zone is a vortex and an eddy is a vortex. Just like a tornado is a vortex. A stream can have an eddy field caused by rocks, and a recirculation zone too. The eddies flowing with the stream can affect the particles in the recirculation zone by running into the outer edges of the recirculation zone.
An eddy dissipates, but a recirculation zone does not.

fruitkiwi May 23, 2012 19:40

Quote:

Originally Posted by mettler (Post 362671)
to the best of my knowledge, a recirculation zone does not move, an eddy moves. A recirculation zone is a vortex and an eddy is a vortex. Just like a tornado is a vortex. A stream can have an eddy field caused by rocks, and a recirculation zone too. The eddies flowing with the stream can affect the particles in the recirculation zone by running into the outer edges of the recirculation zone.
An eddy dissipates, but a recirculation zone does not.

Thank you mettler.
i think recirculation zone is when flow attached to an obstacle. while eddy is subject to high speed flow like tornado. anyway, thanks for sharing knowledge.

unver May 28, 2012 04:15

I think these are all lose terms, and could describe different phenomena at different flow. A "recirculating region" could be a stationary vortex as stated, but on the other hand we always call the unstationary velocity field at the corner of a "backward facing step" as recirculation region. I think recirculating regions occur always attach to a wall due to pressure gradients. if fluid is recirculating in an unbounded fluid, it is rather called VORTEX.

Vortex on the other hand is a general descriptive word for globally rotating field.

Eddy, on the other hand, has a viscous origin. In other words, eddies generated by some sort of shear (so they always has some vorticity). They also describe rotating region of fluid. For example, fluid going down to drain is described by FREE VORTEX, not by EDDY. On the other hand, vortices in the KARMAN VORTEX STREET, can be called VORTEX or EDDY. I am not sure what would be the descriptive difference between vortex and eddy, other than this.

FMDenaro May 28, 2012 05:10

many issues are still debated and misunderstanded ... I suggest starting with this paper http://journals.cambridge.org/action...ine&aid=353418, further discussions are present also in the Lesieur book

fruitkiwi May 30, 2012 02:33

Quote:

Originally Posted by FMDenaro (Post 363400)
many issues are still debated and misunderstanded ... I suggest starting with this paper http://journals.cambridge.org/action...ine&aid=353418, further discussions are present also in the Lesieur book

HI FMDenaro,

Thanks for introducing journal of fluid mechanics, the journal did quite a good job on defining proper term for fluid mechanics.
I agree that we can use an symmetric tensor to help to identifiy a vortex, but when a recirculation or eddy form, it may not always symmetry, A vortex ring may be symmetric since it is a circle. But recirculation region is end result when fluid touch the object, should it be asymmetry?

by the way, Professor Marcel Lesieur done a great work in turbulence. May i share your opinion on which chapter you recommend? as for me, it looks like there are some grey area exists between recirculation region, eddy, and vortex.

FMDenaro May 30, 2012 04:20

I suggest this two books:

1) Lesieur et al. - Large-Eddy Simulations of Turbulence (CUP 2005)

2) Chorin A., Marsden J. A Mathematical Introduction to Fluid Mech.


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