Flow separation
 

Hi,
For flow over circular cylinder, laminar boundary layer separation angle is given as 80 deg (from stag. point) in some books. In some of the literature flow separation angle is given as 125-130 deg (from stag. point).

Now my confusion is

1) Does flow separation and boundary layer separation mean the same?
2)What is the laminar boundary layer sep. angle for cylinder(from stag. point)?

1) yes
2) 2D case or 3D case?

The separation angle is roughly 120 degrees for turbulent flow.

Hi lovecraft22,

Thank you for your answer. I am doing a 2D simulation of flow over cylinder at Re=40(steady laminar). I am not considering boundary layer and my separation angle is around 125 Deg and I found that literature also gives the same results. But in some text books I found that the laminar separation angle is around 80 Deg for cylinder ( don't know whether 2D or 3D). Can you please clarify?

Which textbook are you talking about? It looks a little bit odd that at Re=40 you have separation at 80°…

Hi lovecraft22,

Fluid Mechanics, F.M.White, 4th edition. Page no-455 given as laminar separation at 82 deg.

My 2D laminar flow over cylinder simulation(Re=40) gives separation angle as 125 deg ( which is matching with literature results).

Now my question is , why this difference in separation point? I feel both must be right and I am missing something to understand. Plz clarify.!!!

I've seen the book. It is odd in my opinion to have such a separation at Re=40 but I might be wrong…

At a Reynolds number of 40 the flow state is very different than what White describes in his text. It is laminar, but at Re < 100 the separation forms a closed bubble. For Re > 1000 you get laminar flow with an unsteady wake. From Re = 0 to approximately 100 the separation bubble grows in extent on the downstream side of the cylinder. It sounds to me like you are getting confused because you are comparing two dissimilar situations.

Thanks agd.!!!