$D_h$	hydraulic diameter, m
$Re$	Reynolds number
$L$	channel length, m
$w$	channel width, m
$h$	channel height, m
$w/h$	channel aspect ratio (width/height)
$L_e$	length of the entrance region, m
$L_e/D_h$	dimensionless entrance region length
$u$	velocity, $\mathrm{m}/\mathrm{s}$
$u_{max}$	maximum velocity, $\mathrm{m}/\mathrm{s}$
$y_{max}$	channel half height, m
$u_{FD}$	theoretical fully developed velocity, $\mathrm{m}/\mathrm{s}$
$\mathsf{\rho }$	density, $\mathrm{kg}/{\mathrm{m}}^3$
µ	dynamic viscosity, $\mathrm{Pa}·\mathrm{s}$
ε	rough element height, m
s	adjacent rough elements distance, m