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 cfd_confuse October 2, 2010 03:49

3D mixing tank using MRF/SRF

Hi all,

I am a new user of fluent. Currently, i am facing converging problem with my mixingtank.

This is what i done in gambit:
I have a impeller in a square tank measured 1m by 1m. I have substracted the volume of the impeller (height of hub = 80mm) from the square tank and had split the volume of the impeller with a cylinder measuring 180mm in height and radius=350mm, just enough to cover the entire impeller, to create a moving zone. I then mesh the moving zone w a grid size of 10 and mesh the remaining fluid zone w a grid size of 20. next, i went on to specify the 3 faces of the moving zone as interior so that there is mixing of fluid between the area of moving zone and area outside moving zone.

This is what i done in fluent:
i set the moving zone as a moving reference frame with rotational velocity of 85rpm, with proper rotation-axis origin and rotational axis direction. Then, i set the remaining fluid in the tank as stationary. Next, i set the wall of the impeller to be a moving wall with a rotational velocity = zero relative to adjacent cell zone. (this is the single rotational reference frame model)
For this case, no buffer is needed.

There is some problem converging for the continuity. solution starts to diverge after 6 x 10^-3. i do not know if it is because i set the wrong boundary condition in fluent. can someone enlighten me on what boundary condition to set for this simple mixing tank model? PLEASE HELP ME!!!