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?

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

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

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.