I am putting together an internal flow simulation problem for air flow entering some pipes at a particular volumatric flow rate and exiting to the normal atmosphere. I've done problems like this before and always set up the boundary conditions the same as I'm doing now, but for some reason it is not allowing me to do so and I am constantly getting "face "whatever"-lid is not laying laying on the boundary region between solid and fluid region. It's set up as internal flow, tried one side with volumetric flow on the lids where air is entering and the other side where air is exiting at environmental pressure = 1 atm. Attempt at either boundary conditions refuses to work. Like I said, done this many times before with similar problems and never encountered this. Any thoughts?