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M_W March 18, 2009 12:24

Multiphase in rotating reference frame
 
Hello,

can anyone please give me some advice on the following?
I am working on a centrifugal reactor containing water and air. Air bubbles radially from the outer diameter to the center.
For now I am just simulating in 2D. I have only activated the multiphase model. For the beginning no turbulence, no energy equation or whatsoever. I chose the Eulerian model but also tried VOF and mixture. Mixture does not work because the slip velocity equation (Manninen) breaks down due to the high relative velocity at the inlet. VOF with geo reconstruct is simply too complex for the amount of bubbles. However Eulerian should.
I use a velocity inlet with 2.32 m/s 100% air. The inlet is located on the outer radius (200 mm) and is 1 mm large. Furthermore there is a pressure outlet at the center and a periodic boundary at the sides (I am only simulating a 5.625 slice of the whole circle).
I use a single rotating reference frame (120 rpm) and everything else is defined within that frame. To initiate the solution I set all velocities to 0 in the reference frame (water is rotating with the chamber). Then I patch the inner part (120 mm) with an air fraction of 1. I calculate with a timestep of 1e-6s. Larger timesteps lead to divergence.
The probem is the following: Whatever I do, gas builds up at the inlet and grows and grows but no air is rising to the center. In fact the air should rise due to the centrifugal force.

To test my case I have also set up a simple 2D rectangular bubble column with the same parmeters and gravity activated instead of the rotation. It still wont work.
Btw: the bubble size is defined to be 3 mm. So some gas should rise somehow....

Thanks for any tips!

Martin


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