Overset Boundary and Region Setting Reference

Boundary Settings

Wall

Dynamic Overset Behaviour

Selects different types of dynamic overset behavior. Apply the dynamic overset behavior options depending on the overset configuration in the model.

Allowable Overset Face States	Corresponding Physics Value Nodes
Active, Inactive Dynamic overset behavior is deactivated. The default setting. The overset hole cutting algorithm determines automatically whether the cells in the background mesh are active or inactive.	None
Active, Acceptor Activates dynamic overset behavior. Depending on position, the cells that are adjacent to the wall boundary are either acceptor cells or active cells. If they are acceptor cells, the wall boundary performs as an overset boundary. If they are active cells, the wall boundary remains unchanged. For more information, see Dynamic Overset Behavior.	None
Active Activates dynamic overset behavior where the cells adjacent to the wall boundary are always active. Thus, the boundary remains a wall boundary. This option is applicable when you have a thin geometrical structure, for example, a baffle in the background or the overset region and a comparatively large geometrical structure in the corresponding overset or background region. Selecting this option prevents problems with the hole-cutting algorithm due to discrepancies in mesh resolution of the background and the overset mesh. For more information, see Artificial Thickening for Thin Structures.	Number of Active Layers Sets the number of cell layers next to the wall boundary that are active. These active cell layers serve as an artificial thickening of thin geometrical structures. You are advised to set the Number of Active Layers so that the total thickness of the layers approximately matches the cell size of the coarse mesh of the other region.

ZeroGapWall

This boundary type is created automatically when you create an overset zero gap interface. It provides the same conditions and values as a regular wall boundary.

Prism Layer Shrinkage Behaviour

Allows you to specify how Simcenter STAR-CCM+ applies prism layer shrinkage for the boundary. Only available when Prism Layer Shrinkage option is activated within the overset interface.

The Shrinkage Behaviour options are:

• Automatic—automatically determines whether the boundary requires prism layer shrinkage.
• Disabled—disables the prism layer shrinkage for this boundary.
• Enabled—enables the prism layer shrinkage for this boundary.

Region Settings

Applies to both background and overset regions.

Physics Conditions

Adaptive Prism Layer Specification

Allows you to control prism layers shrinkage for the region, either automatically using internal algorithms or specify directly the related parameters. Only availabe when you activate Prism Layer Shrinkage on at least one overset mesh interface from this region.

Adaptive Prism Layer Specification Option	Corresponding Physics Value Nodes
Automatic	None Internal algorithms determins automatically Number of Adaptive Prism Layers and Number of Prism Layers in Gap / Number of Zero Gap Layers. No further setting is required.
Specified	Number of Adaptive Prism Layers: Available for regions that include overset interfaces. Specifies the maximum number of prism layers that participate in prism layer shrinkage. Number of Prism Layers in Gap: Available for regions that include overset interfaces. Specifies the minimal number of active prism layers that resolve the gap after shrinking. Number of Zero Gap Layers:Available for regions that include an overset zero gap interface. Specifies the number of remaining cell layers allowed in the gap before they become inactive. You are advised to specify the same Number of Zero Gap Layers value for all regions that participate to the same overset zero gap interface. For a given mesh, this setting allows you to control the width of the zero gap that is filled with inactive cells.

Overset Topology

Controls the overset topology of the regions.

Option	Corresponding Physics Value Nodes
Automatic The algorithm detects automatically which region is background region and which region is overset region.	None
Piston Specific option for applications where a piston moves within a cylinder. The cells underneath the piston are deactivated.	Overset Direction Specification Sets the direction to control overset mesh hole cutting. Specifies the Direction underneath the piston. This part of the background mesh is no longer covered by the piston overset region. However, the cells of this background mesh portion must be deactivated. Normally, the hole-cutting process detects cells to be deactivated only when the background mesh is covered by an overset region. Consequently, the direction in which cells of the background mesh underneath the piston must be deactivated is specified. The direction is specified in the Coordinate System selected in the associated expert property.
Direction Specific expert option for applications where the overset boundary does not completely enclose the overset region and this boundary is curved strongly at the same time.	Overset Direction Specification Sets the Direction to control overset mesh hole cutting. The Direction is specified in the Coordinate System selected in the associated expert property.
Bounded Specific expert option for applications where the overset boundary contains meshless space that is bounded by a wall boundary of the background region.	None