CFD Online Discussion Forums - Setting up pressure BC's and calculating local Cf in FLUENT

Hello,

I am looking to simulate the flow over a flat plate in 3D with pressure boundary conditions, and I have two questions.

1. For some context, I have separated the domain into two fluid regions, the bottom region is for the boundary layer, and the top is for the undisturbed flow. What type of boundary conditions in fluent should I apply to specify the pressure and prevent reverse flow? I have included some images of the named selections and the boundary conditions that result in Fluent; I'm not sure if this is sufficient.
Attachment 94745
Attachment 94746
Attachment 94747
2. I need to calculate the local skin friction coefficient along the wall. In this post

Quote:

Originally Posted by Abhinand (Post 756604)

Skin friction coeff : From fluent (as field variable) By calculation : tau = mu*(dx-velocity-dy)

the field variable is compared with the shear stress calculation. How do I define an equation in Fluent to calculate Cf = tau/(0.5*rho*V^2)? This equation would give Cf for the whole plate, but I need to know Cf based on V at different x locations, and I can't choose the velocity at the wall because of no-slip. I'm not sure which V(x) I should use, I was considering using it at the top of the zone where I know the boundary layer will fit into it but I would not know how to program that in. If I can't program it in then I could use the velocity data after the simulation runs.

Sorry for rambling.