Learning Forum

[617283443]

Hi experts!

Why is the option of “Prevent Reverse Flow” at the pressure outlet available in single-phase flow, yet absent when Eulerian or VOF multiphase flow is enabled? How can Reverse flow at the outlet be prevented in Eulerian or VOF multiphase flow?

[SRP]

Hi,

In Ansys Fluent, the 'Prevent Reverse Flow' option at the pressure outlet is available for single-phase flows but is not supported when using Eulerian or VOF multiphase models. This is because the mechanism behind 'Prevent Reverse Flow'—erecting artificial walls at the outlet to block backflow—is not compatible with the complex phase interactions and flux calculations required in multiphase simulations. In multiphase models, the solver must handle phase-specific fluxes and volume fractions at boundaries, which makes the artificial wall approach impractical and potentially unphysical for these cases.

Setting the backflow volume fraction of a particular phase to zero ensures that only the other phase(s) can enter the domain during reverse flow. Incorrect specification can lead to instability and unphysical results.