Six DOF Solver in Dynamic Mesh

What do the “On” and “Passive” options in the 6DOF solver mean?

When the 6DOF solver is activated in Dynamic Mesh > Parameters, “On” and “Passive” check boxes appear under 6DOF Solver Options when specifying a rigid body motion in Dynamic Mesh > Zones. The user can turn off the 6DOF solver if it is intended to specify the zone motion explicitly for any zone (e.g., using DEFINE_CG_MOTION, or DEFINE_GRID_MOTION, or transient profile) and turn on the 6DOF solver if the rigid body motion is a result of fluid forces and moments. By turning on the “Passive” check box for any rigid body zone, the user instructs Fluent software not to include that particular zone in the computation for forces and moments.

For example, it is often necessary to maintain good mesh around a rigidly moving object to resolve the flow structure around it (this is especially important for 6DOF solver, in which the drag forces should be captured accurately). In order to maintain a good mesh around the object, it is customary to have a layer of good-quality mesh cells around it (as shown by the quad cells in the figure attached) and have it move rigidly with the object. Therefore, this layer should inherit the same rigid body motion as that of the object, but it should be excluded from the fluid force calculation. Iin other words, it should move passively with the object.)

Thus, in the above example, the 6DOF solver is turned “On” on both the object wall and the moving layer of quad cells, and “Passive” is turned on for the moving layer of quad cells.