Boundary Layers
A Boundary Layers mesh () is a mesh with dense element distribution in the normal direction along specific boundaries. This type of mesh is typically used for fluid flow problems to resolve the thin boundary layers along the no-slip boundaries.
In 2D, a layered quadrilateral mesh is used along the specified no-slip boundaries.
In 3D, the boundary layer mesh is a layered prism mesh or a hexahedral mesh depending on whether the corresponding boundary-layer boundaries contain a triangular or a quadrilateral mesh.
Additional elements of an arbitrary type can also be inserted into the layers if needed.
To create a boundary layer mesh:
•
In the Graphics window, select the boundaries where you want to insert boundary layer elements. On The Mesh Toolbar click the Boundary Layers button (). This adds a node with the same name, as well as a default Boundary Layer Properties node and at the same time inserts boundary layer elements for the selected boundaries, with the meshed domains adjacent to the selected boundaries as domain selection.
•
In the Mesh ribbon toolbar (Windows) or from the Mesh contextual toolbar (macOS and Linux), click the Boundary Layers button ().
•
Right-click a 2D or 3D Mesh node and select Boundary Layers.
Then enter the properties for the boundary layer mesher using the following sections:
Domain Selection
Specify the domains where you want a boundary layer mesh by first choosing an option from the Geometric entity level list:
•
Choose Entire geometry to specify boundary layer mesh for the entire geometry.
•
Choose Domain to specify the domains for which you want a boundary layer mesh. Choose Manual in the Selection list to select the domains in the Graphics window or choose All domains to select all domains.
Corner Settings
The following options for handling boundary layers at sharp corners are available from the Handling of sharp corners list (in 2D) and the Handling of sharp edges list (3D):
•
Select Splitting (the default) to introduce boundary layer splits at sharp corners. In the Minimum angle for splitting field you specify the minimum angle between adjacent boundary layer boundaries for a split to occur. Control the maximum angle of the elements in the split region by the Maximum angle per split parameter.
•
Select Trimming to trim the boundary layer mesh at sharp corners. In the Minimum angle for trimming and in the Maximum angle for trimming fields you specify the minimum angle and maximum angle, respectively, between adjacent boundary layer boundaries for trimming to occur.
•
Select None to not use any special treatment at sharp corners.
In the Maximum layer decrement field you can specify the maximum difference in number of boundary layers between neighboring points on boundary layer boundaries.
Transition
Select the Smooth transition to interior mesh check box to smooth the transition in element size from the boundary layer mesh to the interior mesh. You can specify the number of smoothing iterations in the Number of iterations field. In the Maximum element depth to process field you can specify the maximum element depth, from the boundary layer interface, for the mesh points to be smoothed.
When a Boundary Layers node is added, a Boundary Layer Properties node is automatically added as a subnode. Use this subnode to specify the boundary layers and the properties of the boundary layers. If you want to specify different boundary layer properties for more than one boundary selection, right-click the Boundary Layers node and add additional Boundary Layer Properties subnodes. However, adjacent boundaries must have the same number of boundary layers.
•
With the Batteries & Fuel Cells Module, see Soluble Lead-Acid Redox Flow Battery (2D): Application Library path Batteries_and_Fuel_Cells_Module/Flow_Batteries/pb_flow_battery.
•
With the CFD Module, see Turbulent Flow over a Backward-Facing Step (2D): Application Library path CFD_Module/Verification_Examples/turbulent_backstep.
•
With the Heat Transfer Module, see Turbulent Flow over a Backward-Facing Step: Application Library path Heat_Transfer_Module/Verification_Examples/turbulent_backstep.
Boundary Layer Properties