# Flow through manifold: convergence issues

I try to simulate flow through a manifold with multiple inlets & outlets but I'm facing convergence issues.

I know that it may be due to poor quality mesh, but my mesh statistics are:

• Minimum Orthogonal Quality = 0.115844
• Maximum Ortho Skew = 0.853992
• Maximum Aspect Ratio = 31.8148e

which doesn't look that bad to me.

Another point could be due to wrong BCs and I'm not sure wether my BCs are good. For the inlets I calculated mass flow in the domain (since the manifold is a physical part from a measurement system, I know roughly what the flow field looks like and what the flow in and out my domain is) and set it as mass-flow-inlet BC. For the outlets I also calculated mass flow and set it as pressure-outlet with a good guess for the initial gauge pressure and a target-mass-flow.

But as I said, I don't get a converged solution, is it due to these BCs?

I attach some residual plots. (I wanted to add more but I can only post 2 links...)

If you need more information let me know, I tried to keep it short.

• After looking at the result in CFD-Post, the flow field looks like expected. But I'm still unsure about the convergence Oct 24 '16 at 8:32
• Pressure based or density based? Did you try different turbulence models? Did you use relaxation factors?
– Algo
Oct 24 '16 at 13:07
• Pressure based, I tried only k-omega with low Re-correction and URFs are: pressure 0.3 density 1 momentum 0.7 turbulent kinetic energy 0.7 specific dissipation rate 0.7 turbulent viscosity 0.9 O2 0.9 NO2 0.9 energy 0.95 So I lowered some URFs, but what should I change to get continuity down? Oct 24 '16 at 13:27
• 1 - You should not be using mass-flow inlet BC with pressure based problems, calculate the velocity from the flow rate and use velocity-inlet BC. 2 - Can you attach a picture of the geometry? Or are you having outlets close to inlets?
– Algo
Oct 24 '16 at 13:35
• I will try it with velocity inlets, and here is a picture from my geometry/mesh pic-upload.de/view-31971232/mesh.png.html Oct 24 '16 at 13:52