Turbomachinery Description and Basic Principles

All energy processes involve the transfer of work and heat in appropriate devices.

In positive displacement machines, which are the subject of various articles in this treatise, this energy exchange takes place by deforming capacities inside which the fluid is temporarily trapped. In turbomachines, flows are assumed to be permanent to a first approximation, which is not the case for positive displacement machines.

Turbomachinery — pumps, fans, compressors and turbines —, which drive larger fluid flows than volumetric machines, play an important role in these energy conversions, acting as a work exchanger between the moving fluid on the one hand, and a mechanical component on the other. The latter has a moving part consisting of a rotor fitted with blades. For example, a turbine is a device for extracting work from a fluid as it expands from a high pressure to a lower pressure.

Compression and expansion turbomachines are machines in which a fluid undergoes a transformation as it flows, partly along fixed ducts forming the machine's stator, and partly along moving ducts belonging to the rotor, which receives or transmits mechanical power as the case may be. These fluid ducts are fitted with blades. In a turbine, the rotor or drive shaft transmits mechanical power to a receiving device, which may be an alternator, pump, compressor, etc., which uses this power for its own purposes.

The aim of this article is to present the different families of turbomachinery, their components and the flows within them. Secondly, it reviews the basic principles required to study them and understand their operation.

This article is the first in a series on turbomachinery [BM 4 281][BM 4 282][BM 4 283].

A glossary and a table of symbols used are presented at the end of the article.