Hi,

I am trying to do CHT analysis of an exhaust manifold. Manifold geometry is not complex. I use polyhedral mesh and my mesh quality is sufficient. There is no sudden growth in cell size(i use grow rate 1.1). Some of my solver's setups are:

-Turbulence Model: SST k-w. (mesh is adjusted to reach y+ value under to 1) -Coupled algorithm. -Gradient: Green-Gauss Node Based -Pseudo Time Method : Off -Exhaust gas is defined as a ideal gas. -Back Pressure is defined to outlet.

I have 3 inlet and 1 outlet.

I used hybrid initialization.  I started the analysis with first order and then switched second order(In the first order part, the analysis was converged and variables that i controlled were stabil.). I iterated with decrease the courant number periodically.(from 200 to 1) After switching to second order scheme residuals and variables started to fluctuate and fluctuation did not finish.

What is the reason of fluctuation? What is solution for convergence and stabilization?

I added residuals and variables plots and journal txt file that i used.

Thanks,