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Continuity does not converge, but mass balance is ok!

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Old   November 28, 2013, 06:26
Default Continuity does not converge, but mass balance is ok!
Join Date: Feb 2012
Location: Leeds, UK
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Hi guys,

I'm running a steady state simulation of a gas turbine combustor with species transport model (the fluids are methane and air at the moment).
I am in the very first stage of the modeling so I am trying to reach a good solution for the "cold" field (i.e. without activating the reactions at all); my problem is that the scaled residuals of continuity got stuck at about 5e-2 and I am not able to enhance this value in any way ( I am using "coupled" for pressure-velocity coupling and I have tried to play with URFs, set all the discretization schemes at first order upwind, tried the pseudo-transient formulation).
However all the other variables are converged, the mass imbalance is very low and the contours of pressure, temperature, velocity etc seems quite reasonable.
The value of the mass imbalance variable are between -4e-7 and 3e-7 in the whole domain.
Do you think I can trust this results even if the continuity equation is not converged? It may be that the scaled residuals are not a good way to evaluate the continuity convergence in this case?

Thank you

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