1. Context

Pneumatic power transmission generally refers to gas dynamics, i.e. the flow of compressible fluids. The flow, i.e. the rate of flow, of air through a network of pipes and components for orienting or controlling this fluid enables power to be transmitted to one or more actuators. The characterization of this flow deserves special attention compared to the flow of liquids. While the flow of incompressible fluids can be studied on the basis of "purely mechanical" considerations, that of compressible fluids necessarily involves "thermodynamic considerations".

Fluid mechanics analyses of high-speed flows of air, gas or steam are incomplete without taking compressibility into account. Indeed, these studies concern flows where the fluid velocity is of the same order of magnitude as the speed of sound. In this case, fluid density can no longer be considered a constant....