This picture was obtained with the default setting. The step size is 3 mm. This shows that while the results are still "correct", the vortex is being "sliced" by the too large step size.
This picture shows "spontaneous" billows that may appear while using the VOF recommended setting. The flat zone on the left is the perturbed zone, at a very high frequency, not leading to instabilities. All the instabilities are the result of "numerical" perturbation. On the right side the effect of the too large step size can still be seen despite the better setting.
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