[MH_Engineer]

I'm trying to solve a relatively easy simulation, water going thru an orifice in a pipe. Its a "2D" simulation, thin pie slice

My results look good, my velocity and mass looks good and pressure drop is what is expected.

But during the solve, P-mass always turns to a F and continues that way. No other warnings or error messages.

Any ideas why Pmass is failing?

[ghorrocks]

In general this FAQ describes it: https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F

But in your case it is likely that the failing equation is either related to the W equation being badly conditioned (as in a 2D simulation the third dimension can be tricky), or the mesh quality from your 2D section is poor. For mesh quality think about whether your slice is too thin.

[MH_Engineer]

Ghorrocks, is P-mass a F the same as a floating point error. I have seen that error before but not this time, it solves normally just P-mass is at F and not OK like the other variables.

Regardless I'll check my mesh and maybe try double precision

[ghorrocks]

The F is a failure of the linear solver to converge. If left unchecked it can get worse until you get a Floating Point error. But if the linear solver convergence is contained you can get away with it.

Yes, double precision might help, and better mesh quality will definitely help. Smaller time step is the other one to look at.