Discussion Forum

Hi,

I am a pretty new comsol User and I am encountering what looks like a pretty easy problem. I am actually trying to simulate a flow in a cylindrical pipe by implementing a Large Eddy Simulation method. My point is to use the general PDE interface to solve the filtered Navier-Stokes equation, in which the small scales are modeled using a basic Smagorinsky model. I am considering a field of 4 independant variables u=(v1,v2,v3,p) where v=(v1,v2,v3) is the filtered velocity and p is the filtered pressure.

My problem is to set the theoretical boundary conditions well. I would like to

-impose a fixed Value of u and a zero gradient of p at the inlet (zero gradient means in that case that dp/dy=0)
-impose a zero gradient of v (dv1/dy=dv2/dy=dv3/dy=0 ) and a fixed value of p at the outlet
-impose a fixed value of v and the orthogonality condition grad(p).n=0 on the walls.

Which would be the best way to achieve this? It seems to me that I have to define 3 constraint boundary conditions (for instance at the inlet, I think that I just have to set R=(v1-c1,v2-c2,v3-c3,d(p,y) where c1,c2 and c3 are the fixed values I want to impose on the velocity) but I would really appreciate to hear from a comsol specialist :)

Thanks in advance.

Gautier