Understanding High Velocities in Far Field of External Flow VOF DPM Simulation – Lesson 5

Why does my external flow VOF DPM simulation exhibit extremely high velocities in the far field?

Like any other external flow simulation, the placement of far field boundaries for these cases is critical. Placement may be even more critical for VOF DPM because of the density changes that occur during phase change.

Care must be taken that the far field boundaries are placed far enough away from the object of interest. If the far field boundaries are placed too close, the pressure boundary conditions that they impose will start to influence the flow field around the object of interest and constrain it in a non-physical way.

Below are some guidelines for far field boundary placement that can be applied to VOF DPM and other classes of external flow problems:

• A standing obstruction with height H & width W, should have far field boundaries of at least 5H and 10W wide.
• The upstream should allow at least 2H of flow development and at least 10H downstream for the wake.
• For airfoils, the domain shape should be parabolic, with dimensions that depend on the airfoil size.
• The inflow should be at a distance of at least 10 chords upstream and the domains should extend 15 chord lengths downstream past the trailing edge.