Is global courant number of 40 too large for transient flow?

Hi


I am using ANSYS fluent VOF model in explicit scheme to run a simulation of two phase fluid of water and co2 in a small hydrophilic channel of 1mm diameter. here the surface tension is very important for me


I have done my best to use the coarsest mesh possible, but yet for 20 secs of simulation it is impossible for me to stick to the global courant number 1 or 2 which is mostly recommended. As at the beginning not much is happening in my simulation and it is just co2 flowing and water being collected (initially water is immobile and it will start moving after some time) would it be ok to use some large global courant numbers like 20 to 40 if I still have like 6 order of magnitude reduction in my residuals or it is simply too large? how about a number like 4?

basically it would be amazing if you could advise me on the largest courant number I can go

Thanks in advance

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