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gpavanb July 12, 2013 11:06

Rotating Frame Boundary Conditions
I am simulating using ANSYS Workbench (14) a heated rotating tank setup which is two concentric thin cylinders with water in between and temperature boundary conditions at the bottom.

The setup looks like a rectangle in the axisymmetric swirl situation. I've set the cell zone to have a rotating frame motion.

The FLUENT tutorial guide suggests that the walls must be stationary for such a rotating tank whereas the help file explicitly states that it must be set as a moving wall (which implies a zero angular velocity relative to adjacent cell zone)

Which one is correct?

Also, for an open top, I've set it as a zero shear boundary. Is it appropriate?

Please mention the corresponding initial conditions as well.

A CFD free user July 17, 2013 03:15

Hey dude
According to my own experience in stirred tank, you don't need to exert a rotation to the walls if you are using absolute reference velocity. The only is required is that you must specify a rotating velocity to the fluid between the cylinders.

Gimlas July 18, 2013 08:19

Dear gpavanb,
By the open top you understand the free surface of liquid in the tank? If yes, and you do not want to simulate swirl creation etc. you should use symmetry BC.

As for the walls. In my simulations of tank with Rushton turbine I use the following approach. I'm creating a separate zone which includes the turbine. The movement of the blades is forced by the MRF method whereas the rotation of the stirrer shaft is achieved by the moving wall settings. I hope that will help.

Best regards

A CFD free user July 19, 2013 03:13

@ Gimlas
You right. But you could've encircled the stirrer shaft into your MRF zone too.
The both is correct.

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