Boundary-Layer Quantities
flow_props computes several standard integral boundary-layer quantities from extracted wall-normal profiles.
Boundary-Layer Thickness
The edge location \(\delta\) is determined from a selected criterion.
Velocity-Ratio Criterion
The default criterion defines the edge where:
\[
\frac{u}{u_e} = \text{threshold}
\]
with a default threshold of \(0.99\).
Enthalpy-Ratio Criterion
An alternative edge is based on total enthalpy:
\[
h_t = c_p T + \frac{1}{2}u^2
\]
and the edge is defined where:
\[
\frac{h_t}{h_{t,e}} = \text{threshold}
\]
Velocity-Gradient Criterion
The third option identifies the edge where the wall-normal velocity gradient falls below a specified threshold.
Displacement Thickness
The compressible displacement thickness is:
\[
\delta^* = \int \left(1 - \frac{\rho u}{\rho_e u_e}\right) d\eta
\]
Momentum Thickness
The compressible momentum thickness is:
\[
\theta = \int \frac{\rho u}{\rho_e u_e}\left(1 - \frac{u}{u_e}\right)d\eta
\]
Shape Factor
The reported shape factor is:
\[
H = \frac{\delta^*}{\theta}
\]
This is the standard integral diagnostic used to compare profile fullness and boundary-layer state.