CFD Boundary Layer Y-Plus Spacing Calculator
Computational fluid dynamics & aerodynamic meshing: Calculate the required first mesh cell height ($Delta y_1$) for target non-dimensional wall distance ($y^+$), wall shear stress, and boundary layer thickness.
Flow Conditions & Geometry
Mesh Spacing & Boundary Layer Metrics
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Frequently Asked Questions
Why is y⁺ = 1 required for k-ω SST but not k-ε?
The k-ε model was formulated for high Reynolds numbers and relies on algebraic empirical wall functions in the log-law region (y⁺ > 30). The Wilcox k-ω and Menter SST models integrate directly through the viscous sublayer all the way to the solid wall, requiring y⁺ ≤ 1.
Does y⁺ vary along an aerodynamic surface?
Yes. Near the leading edge where the boundary layer is thin, wall shear stress τ_w is highest, requiring smaller cell heights. As the boundary layer thickens downstream, τ_w drops, so a constant physical cell height produces decreasing local y⁺ values.
What inflation layer growth ratio is recommended?
A smooth geometric expansion ratio between 1.10 and 1.25 is standard. Ratios exceeding 1.30 cause numerical diffusion and truncation errors at the transition into the unstructured bulk volume mesh.