4. Dynamics

Fluid dynamics is based on the general theorems of the mechanics of material systems and the principles of thermodynamics. The analysis can be carried out at two different scales: one, relating to a macroscopic volume of fluid, called the control volume, is suitable for the engineer seeking a global, approximate solution; the other analysis, which applies to an elementary volume of fluid within the control volume, leads to partial differential equations that can generally only be integrated by recourse to numerical methods. The fields of the characteristic quantities of the fluid are then known within the control volume. The first approach is particularly interesting in the case of permanent flows.