PIV	particle image velocimetry
SHS	superhydrophobic surface
RS	riblet surface
SS	smooth surface
Re	Reynolds number
u	flow velocity (m⋅s−1)
L	length (m)
ν	kinematic viscosity (m2⋅s−1)
‖‖F	Frobenius two-norm of the matrix
${\tau }_{xy}^{+}$	dimensionless Reynolds shear stress
ρ	water density (kg⋅m−3)
u′	fluctuation velocity of streamwise (m⋅s−1)
B	antisymmetric tensor
A	symmetric tensor
ε	a positive parameter
Q max	maximum value of the Q vortex method
U	dimensionless flow velocity
S Ω	total number of a strength vortex
S	total number of all strength vortices
u +	dimensionless velocity
y +	normal dimensionless position
κ	Karman constant
u*	wall friction velocity (m⋅s−1)
y	normal distance (m)
τ	frictional resistance of the microstructured surface (N⋅m−2)
τ 0	frictional resistance of the smooth surface (N⋅m−2)
v′	fluctuation velocity of normal (m⋅s−1)
u ∞	free flow velocity (m⋅s−1)
DR	drag reduction rate (%)