SimScale CAE Forum

Negative Pressure


So I’m using an Incompressible transient LES simulation to model vorticity with an initial condition pressure of 0. I know that the pressure displayed is relative (in post-processing) because in Incompressible Navier-Stokes numerical solvers everything is divided by the density of the fluid. That being said if my initial condition and pressure reference value, as stated in Numerics is zero how can i get a negative value? Is my simulation a total fail and what can i do in the future to avoid this?
Thanks, Anderw


Hi @afowler,

tagging @sjoshi and @gholami here. Maybe they can help you out with that one.




Having negative pressure in incompressible simulations is OK as we are working with pressure differences. In such simulations, you can add any constant to your pressure field and values are still relevant.

By the way, we recently moved to a uniform pressure unit in all simulations. Therefore, even in incompressible, Pascal (Pa) is the unit. We added the term gauge pressure as well to hint that any surrounding pressure, e.g. atmospheric pressure, is not relevant. Having a zero or negative value for gauge pressure is not incorrect in itself.


Pressure Outlet and gauge pressure (Incompressible flow CFD)