Judging convergence
 

Hello everyone,

I have modeled flow past a cylinder with Fluent. I need some advice in terms of judging convergence.

The flow is turbulent using the K-w-sst turbulence model. I also changed the "under-relaxation factor" as instructed in user guide:
"If unstable or divergent behavior is observed, however, you need to reduce the under-relaxation factors for pressure, momentum, k, and epsilon from their default values to about 0.2, 0.5, 0.5, and 0.5"

I don't understand what this convergence history means. (Please see the attached photo). The solution is converged but I'm not sure what the fluctuations imply.

I appreciate any comments.

Cheers
Zeinab

It seems alright. You're solving a transient fluid flow, in this kind of problems the solver uses the result of the converged iteration in previous time step as a first guess ( what we call initialize in fluent) for the next one. so suddenly the the residuals soar then drop and converge .