2.5-D axisymmetric channel flow
 

I am trying to simulate a visco-elastic flow through a straight channel and therefore I am wondering which boundary conditions I have to use. The cross-section is a square and there are two walls and two planes of symmetry. The mesh is one cell thick (2D). How can I realize a flow normal to the channel cross-section, i.e. which boundary condition should I use for the front and back? I already performed this simulation using ANSYS Polyflow solver and it works quite well. Afterwards I would like to do some lagrangian particle tracking (define two zones at the inlet and follow the layer deformation along the channel). Does anyone have some experience with a similar type of flow? Thank you in advance!

Short question
 

Is there any possibility in OpenFOAM to define a flow rate normal to a 2D cross-section? The cross-section consists of two planes of symmetry and two walls (e.g., the upper right part of a squarish channel).