For an outlet flow boundary in an incompressible flow, would mass-flow-outlet behave the same as velocity-inlet with negative velocity values?
For an incompressible flow, both mass-flow-outlet and velocity-inlet with negative velocity values may behave similarly. However, there is a subtle difference in how these boundary types apply numerically and therefore may sometimes show a variation in convergence trends. Velocity-inlet condition applies the same uniform (negative) value provided in the boundary condition panel on every face of the outlet zone. On the other hand, mass-flow-outlet tries to maintain the Σ(mass-flux*face-area) equal to the specified mass flow rate value. The latter does not necessarily mean that the velocity on every face of the outlet zone will have the same value. Hence, the convergence behavior and outlet velocity profiles may be different between the two cases.
You can access the relevant files by clicking on this link: Download Files
For more details, please refer to the document below: