Hi, I would like to simulate the motion of fine particles of diameter 0.1-1mm within a large container. I have calculated their terminal velocity from Stocks equation to be around 0.5-2 mm/s. CFD simulation returns results of flow velocity varying from 50mm/s at the outlet/inlet and <10mm/s within the volume.
I want to model the motion of the particles using mass tracers but I am confused what values to use for calculating the drag coefficient. Due to the low velocities the Reynolds number appears to be around 0.01 to 0.001 ( I used formulas from http://wikihelp.autodesk.com/Simulation_CFD/enu/20
Also what is the significance of "time step size"? I can't find any explanation about it.