This is such a basic question I'm almost embarassed to ask. I have a simple model with 3 inlets and 1 exit. I've defined atmospheric pressure at all inlets and a volumetric flow at the exit. There is a large flow restriction behind the first inlet, a smaller restriction behind the second inlet, and no restriction behind the third. When I run the analysis, the majority of the flow comes through the third inlet and a small leak through the second inlet, as expected. There is no flow through the first inlet.
When I suppress the boundary conditions for the second and third inlet, I expect that all flow should be coming through the first inlet. There should be a large pressure drop due to the restriction (the medium is air), but the flow should be there. What I actually get is 0 flow through the inlet and exit, even though the outlet flow is one of the boundary conditions. The pressure is atmospheric throughout the entire chamber. Can anyone tell me what I'm doing wrong?
Ok, it was a stupid question. I was not careful with my mesh generation, and the mesh was much too coarse in the area of the large flow restriction. Once I refined the mesh locally in this region, I was able to get some more realistic results.