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[FAQ]

Especially for cavitation cases it is possible that the absolute pressure drops below 0 Pa during some iterations within a time step. It seems that the pressure limiter that can be set in the solution limits panel (Tree: Solution > Controls > Limits… / Ribbon: Solving > Controls > Limits…) is not active. How does Fluent handle such negative absolute pressure for the material properties? Fluent applies this minimum pressure limit only during the calculation of the material properties to avoid invalid values for the density. The calculation of the absolute pressure itself is not limited. Therefore, it is possible that the pressure drops below the defined limiter. Such artificial limiting of the pressure could introduce additional instability to the simulation because it would decouple the results of the different transport equations. While negative absolute pressure is numerically possible, it is unphysical and should be resolved by the end of the time step. If this doesn’t happen, you should investigate the stability of the simulation in more detail. For most cavitating flows, it is recommended to set the pressure limit to a value at or slightly below the lowest saturation pressure in the domain to reduce the effects of low pressure values on the density. This can aid in the stabilization of the simulation. Keywords: absolute pressure, pressure limit, pressure limiter, negative pressure, multiphase, cavitation, density, material property, material properties