Mass imbalance between zones for dynamic mesh

[zoelle.wong]

Hi All!

I have a dynamic mesh (see 1st figure), where I split my domain into a static and moving domain. My fluid is supercritical CO2 and the density is being computed via the Peng-Robinson EoS.  I am observing a large mass imbalance at x=0.04m, which is the location of the mesh interface (see 2nd figure). 

I've tried varying the motion relaxation, implicit update, and scale factor for a fixed time step (see 3rd figure). Of these factors, which "knob" is the best for addressing the density imbalance of a compressible fluid? The manual and documentation says "trial and error", but I was wondering if there are other similar applications or use-cases that have been attempted before so that I'm not shooting in the dark. As always, thank you again so much in advance!

Figure 1: Graph of Case Set-Up

 

Figure 2: Graph of Mass-Balance for last simulation time step for all cells. The static-zone correlates to Zone 1 in Figure 1; the negative-translation-zone correlates to Zone 2 in Figure 1

Figure 3: Values that were used to "smooth" out convergence; this corresponds to Figure 2 and had the lowest mass-imbalance thus far

[Federico]

Hello Zoelle, 

I would suggest reducing the time step size