external pressure direction in Two-phase flow, moving mesh(tpfmm)

Hello every one!

I have a question

I'm trying to build simulation using laminar two-phase flow, moving mesh(tpfmm)

and there is a external fluid interface with external pressure and surface tension.

When I put value in external pressure, I think the direction of pressure will be normal to surface,

but i want it to be just z direction

I have no idea to make the external pressure direction into z direction..

Is there anyone who knows it?

I appreciate any advice!