Variable	Explanation	Characteristic	Unit
$n_{\mathrm{q}}$	flow rate ratio between the two outlets in a single capture unit	value related to fluid flow	1
$Q_{\mathrm{trap}}$	flow rate of the capture channel in a single capture unit	-	${\mathrm{m}}^3/\mathrm{s}$
$Q_{\mathrm{bypass}}$	flow rate of the bypass channel in a single capture unit	-	${\mathrm{m}}^3/\mathrm{s}$
$n_{\mathrm{Q}}$	flow rate ratio between the former and latter capture flow channels in a multi-capture unit	-	1
$Q_j$	flow rate of the jth capture channel in a multi-capture unit	-	${\mathrm{m}}^3/\mathrm{s}$
$\Omega$	design area	geometry-related parameter, defined by the designer	${\mathrm{m}}^2$
$\rho$	fluid density	fluid property parameter	$\mathrm{kg}/{\mathrm{m}}^3$
u	fluid velocity	value related to fluid flow	m/s
$p$	fluid pressure	-	Pa
$\eta$	fluid dynamic viscosity	fluid property parameter	$\mathrm{N}·\mathrm{s}/{\mathrm{m}}^2$
$\alpha$	impermeability of the porous medium	solid material property parameter	${\mathrm{m}}^2$
$\gamma$	design variable	parameter related to optimization	dimensionless
${\alpha }_{\max }$	maximum value of α	parameter related to optimization, a scalar determined by the designer	${\mathrm{m}}^2$
${\alpha }_{\min }$	minimum value of α	-	${\mathrm{m}}^2$
$q$	a positive parameter used to adjust the convexity of the interpolation curve	-	dimensionless
Re	Reynolds number of fluid flow	fluid flow parameter	dimensionless
$J$	objective function of the optimization model	process value related to optimization	J
$\Phi$	energy dissipation in the computation domain	-	J
${\Phi }_{\mathrm{real}}$	energy dissipation of the real flow field	-	J
${\Phi }_{\mathrm{ref}}$	energy dissipation of the reference flow field	-	J
$v^T\left(1-\gamma \right)$	volume of the solid phase material in the design domain	-	${\mathrm{m}}^3$
$b$	volume coefficient, used to adjust the appropriate structural volume	adjustable parameter related to optimization, a scalar defined by the designer	dimensionless
$\theta$	weighting coefficient of the flow constraint	-	dimensionless
${\theta }_0$	initial value of weighting coefficient of the flow constraint	-	dimensionless
$R_i^{\left(k\right)}$	relative error at the ith outlet flow of the kth step	value related to fluid flow	1
${\Omega }_{\mathrm{cell}}$	a circular area reserved for cells	geometry-related parameter, defined by the designer	${\mathrm{m}}^2$
${\Omega }_{\mathrm{C}}$	bypass channel domain	-	${\mathrm{m}}^2$
${\Omega }_{\mathrm{D}}$	design domain	-	${\mathrm{m}}^2$
${\Gamma }_{\mathrm{in}}$	inlet of the capture unit	-	m
${\Gamma }_{\mathrm{out}}$	outlet of the capture unit	-	m
W	inlet width and bypass outlet width	-	m
$W_{\mathrm{trap}}$	capture channel outlet width	-	m
$L_{\mathrm{C}0},L_{\mathrm{C}1},L_{\mathrm{C}2}$	flow channel length	-	m
${\Omega }_{\mathrm{W}}$	designated partial solid area	-	${\mathrm{m}}^2$