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 giack June 29, 2013 12:45

interFoam grid refinement results and parasitic currents

Hi to all,
I obtained some strange results from my simulations. I tested this case:
At the initial time t = 0 the right wall of a closed tube completely filled with liquid is removed, allowing the liquid to exit the domain and, at the same time, allowing the gas to enter. The computational domain is a horizontal tube with diameter D = 0.0508 [m] and length L = 3.0 [m]. My aim is to calculate the velocity of the front of the bubble.
I did a grid refinement in all directions with this results:
20x20x500: high fluctuationg velocity;
30x30x600: smaller fluctuating velocity;
40x40x800: much smaller fluctuating velocity,almost constant (note the solution is a constant velocity)
50x50x1000: high fluctuating velocity.
Note that Nx x Ny x Nz are the number of cells in the x,y and z direction and that the pipe axis is in z direction.

This a strange behavoiur. what is the cause?Is possible that the cause are parasitic currents?

Note that I simulate the problem also with Fluent and it give a constant velocity

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