inlet boundary conditions inside domain
 

Hi, I was running a simulation of a burner in the center of the domain.

The burner was extruded with two patches. The goal is to set a fuel inlet boundary condition on the bottom patch side. For the burner, the top patch velocity is set to zero, and the bottom patch is set with "flowRateInletVelocity" with a positive mass flow rate.

To my surprise, in the results, although most combustion occurs on the bottom patch side which is reasonable, some of the combustions indeed occur below the burner (on the top patch side). Since I was trying to set the top patch as a wall, it is not reasonable to see fuel on this side

So I am wondering if the "flowRateInletVelocity" allows flow across it? And anyone could help and suggest a reasonable boundary condition for the burner