${\partial }_t$	Time derivative operator, $\left[1/\mathrm{s}\right]$
$\nabla$	Gradient operator, $\left[1/\mathrm{m}\right]$
$A$	Channel cross-sectional area, $\left[{\mathrm{m}}^2\right]$
$c_P$	Specific heat capacity, $\left[\mathrm{J}/\mathrm{kgK}\right]$
$CFL$	Courant–Friedrich–Lewy number, dimensionless
$D_h$	Channel hydraulic diameter, $\left[\mathrm{m}\right]$
${\epsilon }_r$	Relative wall roughness, dimensionless
$\epsilon$	Turbulent dissipation rate, $\left[{\mathrm{m}}^2/{\mathrm{s}}^3\right]$
$f$	Frequency, $\left[\mathrm{Hz}\right]$
$f_D$	Darcy friction factor, dimensionless
$\eta$	Kolmogorov length scale, $\left[\mathrm{m}\right]$
$k$	Thermal conductivity, $\left[\mathrm{W}/\mathrm{mK}\right]$
$k$	Turbulent kinetic energy, $\left[{\mathrm{m}}^2/{\mathrm{s}}^2\right]$
$\lambda$	Taylor length scale, $\left[\mathrm{m}\right]$
$L$	Channel length, $\left[\mathrm{m}\right]$
$\mu$	Dynamic viscosity, $\left[\mathrm{Pas}\right]$
$\nu$	Kinematic viscosity, $\left[{\mathrm{m}}^2/\mathrm{s}\right]$
${\nu }_t$	Turbulent kinematic viscosity, $\left[{\mathrm{m}}^2/\mathrm{s}\right]$
$\omega$	Angular frequency, $\left[\mathrm{Hz}\right]$
$\omega$	Specific turbulent dissipation rate, $\left[\mathrm{Hz}\right]$
$O$	Channel perimeter, $\left[\mathrm{m}\right]$
$P$	Pressure, $\left[\mathrm{Pa}\right]$
$\Delta P$	Pressure difference, $\left[\mathrm{Pa}\right]$
$Q$	Volumetric flowrate, $\left[{\mathrm{m}}^3/\mathrm{s}\right]$
$\rho$	Mass density, $\left[\mathrm{kg}/{\mathrm{m}}^3\right]$
$R$	Flow resistance, $\left[\mathrm{Pas}/{\mathrm{m}}^3\right]$
$\mathrm{Re}$	Reynolds number, dimensionless
$\Delta t$	Time step size, $\left[\mathrm{s}\right]$
$\tau$	Period of the breathing cycle, $\left[\mathrm{s}\right]$
${\tau }_{\eta }$	Kolmogorov time scale, $\left[\mathrm{s}\right]$
${\tau }_{SGS}$	Subgrid-scale stress tensor, $\left[\mathrm{Pa}\right]$
${\tau }_w$	Wall shear stress, $\left[\mathrm{Pa}\right]$
$T$	Temperature, $\left[\mathrm{K}\right]$
$u$	Flow velocity vector, $\left[\mathrm{m}/\mathrm{s}\right]$
$u$	Flow velocity, $\left[\mathrm{m}/\mathrm{s}\right]$
$u_{\tau }$	Shear velocity, $\left[\mathrm{m}/\mathrm{s}\right]$
$\Delta x$	Grid size, $\left[\mathrm{m}\right]$
$y$	Distance to the wall, $\left[\mathrm{m}\right]$
$\mathrm{Wo}$	Womersley number, dimensionless
In silico	In a digital computer model, e.g., CFD
In vitro	In a physical replica
In vivo	In a living patient
AR	Acoustic rhinometry
AAR	Active anterior rhinomanometry
AHI	Apnea–hypopnea Index
CFD	Computational fluid dynamics
CT	Computed tomography
DNS	Direct numerical simulation
LB	Lattice–Boltzmann
LES	Large eddy simulation
MRI	Magnetic resonance imaging
NAO	Nasal airway obstruction
NR	Nasal resistance
NS	Navier–Stokes
NOSE	Nasal obstruction symptom evaluation
OSA	Obstructive sleep apnea
PNIF	Peak nasal inspiratory flow
RANS	Reynolds-averaged Navier–Stokes
RMM	Rhinomanometry
VAS	Visual analogue scale