[D.B]

Hi All,
I am simulating a 2D-laminar flow over a flat plate case using icoFOAM. My domain is a constant velocity inlet. Initially there is a free-slip region at the base(zero gradient) followed by wall after some distance(to allow for flow adjustment).

BC's
a) I have tried zero Gradient and advective BC at outlet for velocity.

b) I intend to apply a zero vorticity BC at the top. I do this by giving a profile for V velocity as V = v(x) and specifying dU/dy = v'(x). I enforce this by giving a directionMixed BC with
value fraction = ( 0 0 0 1 0 0).


Observations
Note : I extract the vorticity data by using the utility vorticity.

a) Now, ideally I should get zero-vorticity at the top boundary at the top, instead I get a large vorticity at the top, the shape of which is same as -dU/dy that I give. ( See the vorticity and refGrad plot along top boundary as shown below)

Vorticity_plot_300x200.jpg

b) I have huge reflections in vorticity from the top and exit boundaries (see fig) which are seen only in vorticity and not other basic variables like velocities and pressure. I have tried advective BC but to no avail. Even changing the domain size doesn't remove the reflections completely

Vorticity_300x200.jpeg


Questions

1) My first doubt is if the directionMixed BC is applied correctly and if Gradients are being properly enforced since the vorticity is primarily of order of -dU/dy
2) How do I eliminate the reflections ???

3) Is there a way to extract various velocity gradients in OpenFOAM

I hope someone can help me solve my problem.