ABSTRACT
Fluid motion is governed by the conservation of mass (continuity) equation and the conservation of momentum (Navier-Stokes) equation. The flow of air in the respiratory airways is usually assumed to be incompressible.1 For incompressible flow, the continuity equation is given by
∇·V0 (8.1)
and the Navier-Stokes equation is
ρ (V·∇)Vρ f ∇pµ∇2V (8.2) where ∇ and ∇2 are the gradient and Laplacian operators, respectively (defined below), ρ is the fluid density, µ is the absolute fluid viscosity, and p is the hydrodynamic pressure. The parameter f is any externally applied volumetric force, such as gravity.
