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-   -   How to find the seperation region? (http://www.cfd-online.com/Forums/cfx/24628-how-find-seperation-region.html)

 Omer October 7, 2007 16:39

How to find the seperation region?

I am working on a mixing type of T Pipe Junction flow problem. As we know as the flow passes through the branch into the main header, there is seperation and recirculation downstream of the junction. How do I find out about the size of the seperation bubble? I have two options but both give me different results.

1. Do I look at places where the pressure is negative? A longer region

2. Do I look at places where the velocity is negative? A shorter region compared to former.

Or am I mixing recirculation with seperation? Does it mean, seperation ends when velocity attains a positive value at the wall boundary. And Recirculation is the region where the pressure is negative?

 Glenn Horrocks October 7, 2007 18:52

Re: How to find the seperation region?

Hi,

In 3D there is no general definition of a separation (at least none I am aware of). It is problem dependant - sometimes an isosurface with a slight negative velocity against the flow direction is useful, sometimes the wall shear stress can pick it up, at least the separation/reattachment lines.

Glenn Horrocks

 Omer October 7, 2007 23:45

Re: How to find the seperation region?

Thanks a heap Glenn.

I never realised that creating an isosurface could be so helpful. I was trying to do it the old way, you know by plotting velocity profiles along the length. But this surely is a lot better, making it easier to do it as well as to visualize the flow field!

Plenty thanx again

Omer

 Wei Chen October 8, 2007 08:12

Re: How to find the seperation region?

i think you should look up the distribution of the velocity u gradient y,if it is equal to zero. there is the seperation place.

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