2. General equations for three- and two-dimensional cases. Laminar flows.

2.1 Balance equations for three-dimensional flow

The balance equations, known as Navier Stokes equations, apply to both laminar and turbulent flows, provided that the partial equilibrium assumption is satisfied. This assumption, which assumes that the characteristic scale of the flow gradients is large in front of the mean free path of the molecules (, _pm " 0.1 µm for usual gases under ambient temperature and pressure conditions) and that the characteristic time of the flow evolution at a point is large in front of the mean time τ _m separating two collisions τ _m " 10 ^–10 s under the conditions defined...