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fruitkiwi April 12, 2012 04:21

Recirculation region in streamline plot?
Hi,dear all,

Recently stuck in "recirculation region" and "circulation region" ,is there any difference in terms of streamline plot?

I read some text say that recirculation region is defined by closer streamline compared to normal streamline,is it true?

If the flow field is steady, a streamline is a good indicator of flow characteristics such as recirculation zones.

mettler April 12, 2012 08:22

your recirculation zone is going to be concentric circles.

this is flow over a backwards facing step:

fruitkiwi April 12, 2012 20:49

1 Attachment(s)
Hi, Mettler,

Thank you for your fast reply.
Do you call that concentric circle as recirculation area or circulation area?
As circulation area is always formed as long as you have imbalance of velocity or pressure, but how about recirculation area?

The re-term means it flow back, am i right?
do you consider the circle as i attached is recirculation area?

mettler April 13, 2012 10:11

a recirculation zone will be due to the physics of the flow. If you look at the step flow (flwo is from left to right), when the fluid goes over the step it will begin to curve up towards the top wall, as a result there will be flow along the backside of the step due to the low pressure of the moving fluid. This will cause the flow to move along the backside, which will drag some of the fluid along the top wall. This flow then gets entrained in the moving flow, thus causing a circulation zone..also, a stagnant zone. I think your zones of imbalance are not the same because they dissipate and are not located in the same spot, right? I am think of eddies - is that what you have?

fruitkiwi April 14, 2012 16:30

Dear Mettler,

sorry for late reply, as i am try to understand it.
Yes, there is what i have.A strong fluid jet come from top and when the fluid travel down for a short distance, it hit the tube, some fluid go into the tube, others go outside and form the circle.

But it is running in the laminar flow model, will it experience the viscous dissipation?

as the i set the viscoity to 0.00005, a vely low viscosity.

I read through the eddy flow , it is due to the
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. from wiki
so i make the following statement about my result
"a strong fluid jet come from top, when it hit the tube, the tube cause the eddy flow, the eddy flow form a vortex beside a tube and leads to formation of recirculation region"
can i link the eddy flow, vortex and recirculation region together?

mettler April 14, 2012 16:56

a recirculation zone will not will always be there. I think you just have an eddy. The eddy should travel with the flow and dissipate. But, if the zone doesn't move and continuously re-circulates, then that is a 'recirculation zone'. If that is the case, I would say that the tube causes a recirculation zone to form beside the tube. (or where it is)

fruitkiwi April 15, 2012 20:54

Hi, Mettler,

Thank you very much, it really exactly what you describe when i am able to play the animation.and after few google search, i fully agree with your explanation.

Now leave one last question,
I found
"eddies are shed continuously from each side of the body, forming rows of vortices in its wake."

can i conclude that the circle is a vortex which caused by eddies?
i only see a circle form throughout my simulation.

mettler April 15, 2012 22:02

an eddy is a vortex. It just dissipates. Think of a tiny whirlpool. The next time you are by a small creek you can see them caused by the rocks or sticks..

fruitkiwi April 16, 2012 01:41

Hi, Mettler,

Thanks for solving my question.
All problem solved.

start to fall in love with beauty of CFD.thanks:)

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