API Reference

CFDPre’s public interface is the single function yhgrcalc, importable directly from the package:

from cfdpre import yhgrcalc

---

yhgrcalc

yhgrcalc(
    fluid,
    temperature_c,
    pressure_bar,
    massflow_kgpersec,
    hydraulicdia_mm,
    target_yplus,
    num_layers,
    flow_type="internal",
    flow_velocity_mpersec=None,
    bl_thickness_mm=None,
    bl_thickness_fraction=None,
    roughness_mm=0.0,
)

Calculate boundary-layer mesh sizing — first layer height, growth ratio, and final layer thickness — for a given fluid, flow condition, and target \(y^+\). See Theory & Methodology for the underlying physics.

Parameters

Name	Type	Default	Description
fluid	str	—	CoolProp fluid name, e.g. "Air", "Water".
temperature_c	float	—	Static temperature in degrees Celsius.
pressure_bar	float	—	Static pressure in bar (absolute).
massflow_kgpersec	float	—	Mass flow rate in kg/s (used for internal flow).
hydraulicdia_mm	float	—	Hydraulic diameter (internal) or characteristic length (external), in mm.
target_yplus	float	—	Target \(y^+\) at the first cell centroid.
num_layers	int	—	Number of inflation / prism layers, \(N\).
flow_type	str	"internal"	"internal" (pipe/duct) or "external" (flat-plate/aero).
flow_velocity_mpersec	float, optional	None	Free-stream velocity in m/s. Required for flow_type="external"; ignored for internal flow.
bl_thickness_mm	float, optional	None	Explicit total prism-stack thickness in mm. Overrides the default \(\delta_{99}\).
bl_thickness_fraction	float, optional	None	Internal only. Prism-stack thickness as a fraction of pipe radius, in \((0, 1]\). Ignored if bl_thickness_mm is given.
roughness_mm	float	0.0	Absolute wall roughness in mm for the Haaland turbulent internal correlation. 0.0 = hydraulically smooth.

Returns

A dict with the following keys. Inputs are echoed back; computed quantities are grouped at the end.

Key	Description
fluid	Echoed input.
temperature [C]	Echoed input.
pressure [bar]	Echoed input.
massflow [kg/sec]	Echoed input.
hydraulicdia [mm]	Echoed input.
target yplus	Echoed input.
number of layers	Echoed input.
flow type	"internal" or "external".
roughness [mm]	Echoed input.
dynvisc [N-sec/m^2]	Dynamic viscosity \(\mu\).
thermal conductivity [W/m-k]	\(k\).
specific heat [cp] [J/kg-k]	\(c_p\).
density [kg/m^3]	\(\rho\).
kinematic viscosity [m^2/s]	\(\nu = \mu/\rho\).
flow velocity [m/sec]	Bulk (internal) or free-stream (external) velocity \(V\).
reynolds number	\(Re\).
prandtl number	\(Pr = c_p\mu/k\).
skin friction coefficient [cf]	Fanning skin-friction coefficient \(c_f\).
wall shear stress [tau_wall]	\(\tau_w\) in Pa.
boundary layer thickness [delta99] [m]	Total thickness \(\delta_{99}\) spanned by the stack.
height of cell centroid from wall [yp] [m]	First-cell centroid height \(y_p\).
first layer height [yh] [m]	First layer height \(y_H = 2y_p\).
Growth Ratio	Geometric growth ratio \(r\) (nan if unresolvable).
Final Layer Thickness [m]	Outermost layer thickness \(y_H r^{N-1}\) (nan if unresolvable).

Raises

• ValueError — if flow_type is not "internal"/"external", if flow_type="external" is used without flow_velocity_mpersec, or if bl_thickness_fraction is outside \((0, 1]\).

Warns

• UserWarning — if the resulting growth ratio exceeds ~1.3, or if the boundary-layer thickness is not larger than the first layer height (inputs inconsistent; growth ratio and final layer thickness are returned as nan).

Examples

Internal pipe flow (default):

from cfdpre import yhgrcalc
yhgrcalc("Air", 50, 10, 2.5, 125, 1, 8)

Internal flow, prism stack limited to 30 % of the radius:

yhgrcalc("Air", 50, 10, 2.5, 125, 1, 8, bl_thickness_fraction=0.3)

External flat-plate flow (velocity required):

yhgrcalc("Air", 25, 1.01325, 2.5, 1000, 1, 15,
         flow_type="external", flow_velocity_mpersec=30)

---

Auto-generated API docs

This reference is currently hand-maintained. Once the updated library is published, it can be switched to pull directly from the source docstrings via Sphinx autodoc — the configuration (napoleon, autodoc) is already wired up in conf.py. The equivalent directive would be:

::: {eval-rst}
.. autofunction:: cfdpre.yhgrcalc

:::