urgent: velocity in two phases models

Hi all,
I m trying to simulate a two phase models (fluid+empty) and I need to impose a velocity to the fluid phase.
can someone please tell me how can I introduce this velocity?
I think that in the DamBreak example the fluid velocity is introduced as the ratio delta_x / delta_t ? is that right??
any help will be appreciate. thinks

I think that this instruction can impose the initial velocity to the fluid in two phases model:
setToConstant<T,3>(j, domain, Array<T,3>(0.1,0.,0.)).
is that right?