Boundary Layer Refinement

Boundary Layer Refinement#

Boundary layer refinement generates prismatic layers near wall surfaces to accurately resolve viscous effects and boundary layer phenomena, which is crucial for capturing wall shear stresses, heat transfer, and flow separation. The Boundary Layer refinement overwrites the general boundary layer settings set in meshing defaults.

Available Options#

Option

Description

First layer thickness

Height of the initial prismatic layer

Assigned surfaces

Target surfaces for boundary layer application

Detailed Descriptions#

First Layer Thickness#

Specifies the height of the initial prismatic layer adjacent to the wall.

  • Required

  • Example: 1e-5 m

Note: Critical for achieving desired \(y^+\) values and resolving viscous effects. \(y^+\) is a non-dimensional distance that measures how well your mesh resolves the flow boundary layer. Because it relies on wall shear stress, its value changes dynamically with flow velocity and fluid properties, not just mesh size. See y+ estimation for formulas to estimate the required first layer thickness.

Assigned surfaces#

Identifies the wall surfaces where boundary layer refinement will be applied.

  • Required

Notes:

  • Must reference valid wall surface entities in the geometry.

  • Assign the boundaries by selecting from the list using the + button or select graphically in the viewer region.

💡 Tips

  • Set first layer thickness based on desired \(y^+\) value and flow conditions. Remember that \(y^+\) changes dynamically with flow velocity and fluid properties, not just mesh size.

  • Use growth rates between 1.1 and 1.3 for optimal resolution

  • Consider Reynolds number when determining layer thickness

  • Ensure sufficient layers for boundary layer development

  • Balance resolution requirements with computational cost

❓ Frequently Asked Questions

  • How do I determine appropriate first layer thickness?

    \(y^+\) is a non-dimensional distance that measures how well your mesh resolves the flow boundary layer. Because it relies on wall shear stress, its value changes dynamically with flow velocity and fluid properties, not just mesh size. Calculate based on desired \(y^+\) value, Reynolds number, and flow conditions using appropriate scaling laws. For resolved approach, target \(y^+ \approx 1\). For wall functions, target \(30 < y^+ < 300\). See y+ estimation for detailed formulas and calculation methods.

  • What happens if boundary layer refinements overlap?

    The finest (smallest) first layer thickness will be applied in overlapping regions.

🐍 Python Example Usage

 
from flow360 import BoundaryLayer, u

# Boundary layer refinement for wing
bl_ref = BoundaryLayer(
    name="wing_bl",
    faces=[wing_surface],
    first_layer_thickness=1e-5 * u.m,
)

# Boundary layer refinement for high Reynolds number flow
high_re_bl = BoundaryLayer(
    name="high_re_bl",
    faces=[high_re_surface],
    first_layer_thickness=1e-6 * u.m,  # Smaller for higher Reynolds number
)
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