CFDPre

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Open-source boundary-layer mesh sizing for CFD — first layer height, growth ratio, and final layer thickness, computed with the correct correlations for internal (pipe/duct) and external (flat-plate/aero) flows.

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CFDPre is an open-source Python library for boundary-layer mesh sizing in Computational Fluid Dynamics (CFD). Given your fluid, flow conditions, and target \(y^+\), it computes the three numbers you need to set up an inflation / prism layer stack in a mesher such as OpenFOAM (snappyHexMesh), Fluent, or cfMesh:

  • First layer height — the wall-adjacent cell thickness that achieves your target \(y^+\)

  • Growth ratio — the geometric expansion ratio between successive layers

  • Final layer thickness — the thickness of the outermost layer in the stack

Fluid properties are evaluated with CoolProp, so you can work with real fluids (air, water, fuels, refrigerants, …) at a given temperature and pressure instead of hand-typing density and viscosity.

Why it exists

Sizing the near-wall mesh is one of the most repeated calculations in wall-bounded CFD, and getting it wrong quietly corrupts your turbulence model and wall functions. CFDPre turns the full chain — fluid properties → Reynolds number → skin friction → wall shear → friction velocity → first layer height → growth ratio — into a single call, with the correct correlations for internal (pipe/duct) and external (flat-plate/aero) flows.

Quick example

from cfdpre import yhgrcalc

result = yhgrcalc(
    fluid="Air",
    temperature_c=50,
    pressure_bar=10,
    massflow_kgpersec=2.5,
    hydraulicdia_mm=125,
    target_yplus=1,
    num_layers=8,
)

print(result["first layer height [yh] [m]"])  # -> 5.21e-06
print(result["Growth Ratio"])                 # -> 3.66  (with a UserWarning: too aggressive)

Installation

pip install cfdpre

Where to next

Installation Requirements and install options Quickstart Internal and external flow, in code Theory & Methodology Every formula CFDPre uses, derived and referenced API Reference Full yhgrcalc signature and outputs

Coming soon

CFDPre currently gives you the numbers — what’s next is wiring them straight into your mesher’s config:

  • OpenFOAM — generate a ready-to-paste addLayersControls / snappyHexMeshDict snippet

  • Fluent / cfMesh — equivalent inflation-layer setup snippets

  • Batch / parametric sweeps — vary velocity or geometry over an array and get a table of results