For a 2D flow simulation, open SpaceClaim and use Sketch to draw a rectangle on the XY plane, then exit the sketch and return to 3D and you will have a surface.  Use Sketch again and select that surface to sketch on again. Draw a rectangle starting on the Inlet side of the surface and make the height the size of the inlet you want. The width can be all the way over to the opposite side. Repeat that on the Outlet side. Exit the sketch and return to 3D.  You will now have an edge on the inlet side and an edge the outlet side to use in the flow simulation. It doesn’t matter that the rectangle is divided into 5 faces.