[Chander]

Hi,

I am performing a steady state simulation. At low Re, i am able to get convergence by using a small physical timescale of 1e-4 s. At higher Re, I start the simulation with the same physical timescale. However, I have to progressively reduce the timescale to reduce the residuals. Please refer the attached figure for the behavior of the momentum residuals. I impose a convergence criteria of 1e-6 and a conservation target of 0.1%.

1. With the physical timescale of 1e-4 s, residuals stabilize and I reduce the timescale to 1e-5 s. The residuals reduce but again stabilize at a lower level.

2. Then I gradually reduce the timescale to 1e-9 s but it has no effect on the residuals.

3. On reduction of timescale further to 1e-10 s and 1e-11 s, the residuals reduce sharply (within 2-3 iterations of reduction of residuals each time) but again stabilize at lower level.

4. Finally, when I reduce the timescale to 1e-12 s, residuals reduce sharply in the very next iteration to below the convergence criteria and the simulation stops giving the message that the convergence criteria and conservation targets have been met.

These sudden reductions with residuals seem very unreal. Has the simulation actually converged or I am looking a numerical instability which is just fortuitously resulting in a somewhat false reduction of residuals?