[mannou]

Hi openfoamers

I would like to study the flow at rest in a tube and I want to specify at the inlet a pressure equal to 0 and for the velocity I want it to adapt with the pressure without assigning a value, how I can define the boundary conditions (inlet) for speed? any help will be appreciated

[mannou]

Is there anyone who worked in this case please ??

[Lorenzo210]

Try this:
https://www.openfoam.com/documentati...ctorField.html

[sqek]

More generally, for any field where you want the solver to adapt it instead of forcing a value, use zeroGradient.
zeroGradient sets the boundary value equal to the neighbouring cell when updated, so basically doesn't try to change the value and lets the cell decide it itself.
For velocity, pressureInletOutletVelocity can be more stable - it's the same as zeroGradient for outflow, but for inflow it sets a tangential velocity (so if you set tangential velocity to zero, it forces inflow to be perpendicular to the boundary).
There are also some derived versions like pressureNormalInletOutletVelocity (for inflow, velocity is always normal to the boundary)

But if you want the direction of any flow into your tube to not be constrained, use zeroGradient, if this gives weirdness near the edges or is unstable try one of the pressureInletOutletVelocity ones instead.