bubbly flow: udrift in laminar flow...

Hi,

I am currently working with the bubbly flow application mode in a laminar flow.

The gaz velocity, ug, is computed thanks:
ug=ug+uslip+udrift

In the help, is it said that the drift velocity is computed only in a turbulent flow. However, in the laminar flow, we can see that this dift velocity is non equal to zero. Does anyone know if, from a physical point of view, if this velocity should be equal to zero in a laminar flow?

thanks a lot!

Patrick

PS: in version 3.5, the drift velocity was equal to zero in a laminar flow