Tube diffusion

Hello all,

So I have flow through a cylinder, and want to inject some sort of dye into it. I made a cylinder, and then extruded a circle on the edge to simulate the injection point where I will have some sort of inflow or flux of concentration. For some reason the mesh is not generating around the circle. I'm not sure if I did it right, but any suggestions would be helpful! I attached the file if anyone wants to look. Thanks!

Jon