Explicit Resistive Pressure Outlet Boundary Condition

Many industrial and biological systems consist of a network of pipes and chambers of different sizes. Because of its configuration, a complete CFD analysis of such systems is normally impractical, and only regions of interest are simulated. Simulations of regions of interest can be performed with accuracy only if the boundary conditions (BCs) are experimentally measured. However, this is not always possible, specially if the simulation is trying to predict the hydrodynamic performance of a device in its design stage. To that end, the hydrodynamics inside the region of interest (i.e., in the CFD domain) is coupled with the hydrodynamics outside the region of interest, which would alter the BCs. Velocity and pressure waves travel into the region of interest, where they are transformed by the CFD simulation, and they continue being damped, dispersed and reflected downstream from the CFD domain. As a consequence, solutions to the governing equations in the CFD domain are highly dependent on the outflow BCs imposed to represent the rest of the system downstream of the region of interest. The importance of modelling the dynamics of the downstream region has been demonstrated in publications of haemodynamics, but it is equally important in industrial cases.