Adding Refinement Boxes¶
Refinement boxes are cuboid regions within the domain where the lattice realizes a step change in resolution and timestep. Such zones are particularly useful in modeling systems with high aspect ratio features, such as small openings in large vessels or small impellers inside large tanks. When applied judiciously, refinement boxes can offer multiple order-of-magnitude decreases in simulation runtimes, as compared to uniform mesh simulations.
Refinement boxes are added to the domain via Build->Add Refinement Box.
Once created, refinement boxes can be moved, scaled, copied, or deleted by right-clicking the icon in the model tree.
- Level Number
This value defines the degree of refinement. The lattice spacing and time-step inside each refinement box is equal to the far-field values (listed under the Simulation menu) divided by 2^(Level Number). For example, if the Level Number is set to 1, the resolution and time-step within the refinement box will be 1/2 that of the far-field. If the Level Number is set to 2, the the resolution and time-step within the refinement box will be 1/4 that of the far-field.
Regions with multiple refinement boxes must follow a Russian nesting doll configuration. That is, a refinement box of Level 2 must be surrounded by a refinement box of Level 1 and cannot interact directly with the far-field (Level 0). Likewise, a refinement box of Level 3 must exist between boxes of Levels 2 and 4.
Above three or four boxes, the additional communication costs associated with each refinement box can exceed the computational savings associated with the reduction in total lattice count.
Refinement should be used as a mechanism for enhancing near field resolution, not starving the far-field resolution. If the far-field is under-resolved, spurious motions will appear at the boundaries of refinement zones.
At short times, turbulence inside the refinement box will be better resolved than flow outside the box. At longer times, as the bulk flow becomes increasingly turbulent, the boundary will become less apparent. See: https://mstarcfd.wistia.com/medias/qcgtuc5p0m
- Fluid Box Point 1
Refinement box lower corner. Coordinates shown in selected Template units.
- Fluid Box Point 2
Refinement bounding box upper corner. Coordinates shown in selected Template units.
- Refinement Lattice Dx
Lattice spacing within the refinement box
This value cannot be edited directly, as it is defined by the resolution of the main lattice.
- Refinement Lattice Dt
Lattice timestep within the refinement box
This value cannot be edited directly, as it is defined by the timestep of the main lattice.