Initializing. Convergence jump.
 

Hello

There is an option in Fluent in the "Calculation activities" which allows to use ".dat" file as an initial solution. I need it in order to start FSI with a stabilized Fluent solution.
The problem is when I use it in the same case, continuity residuals are higher than they shall be. This is not just for several initial time steps, it is so all over the whole solution. Pressure monitor at the point look converged, but continuity residual has value of 2e-3 after 40 iterations instead of 1e-4 after 20 iterations.

Could anyone explain why that happens? What should I do?

The default setting for the continuity residual is to be scaled by its maximum value in the first five iterations. If you start with a better initalization, the value you are scaling by will already be smaller, so the scaled residual when it has converged will be larger.

You can read more in the User's Guide, section 28.15.

Thank you a lot Andrew!