Turbomachines. Energy analysis with applications

As with any real fluid flow, the flow in a turbomachine is subject to irreversible frictional losses. These losses affect not only the fixed and moving blade rings, but also the ducts that guide the fluid in and out of the machine, or connect two successive stages.

By design, there are also leakage losses, as it is necessary to maintain clearance between fixed and moving parts. These losses are often difficult to quantify, as designers have to introduce aerodynamic obstacles to reduce the flow. What's more, these leakage flows interfere with the main flow when reintroduced into the machine at the appropriate point.

The actual power absorbed by a compression machine is always greater than that of a perfect, lossless machine operating between the same pressure levels. Between the same pressure levels, an expansion machine delivers less power than would be expected if the machine were perfect.

The aim of this article is to explain the origin and nature of the losses that affect energy exchange in a turbomachine. These are losses in the mechanical sense, i.e. the dissipation of mechanical energy into heat.

We then define yields, which characterize the extent of losses in energy transfer.

An application involving an axial turbine concludes this article, summarizing the concepts recalled or developed earlier.

This article is the last in a series devoted to turbomachinery:

•[BM 4 280] – Turbomachinery – Description and basic principles ;

•[BM 4 281] – Turbomachinery – Energy conversion mechanism ;

•[BM 4 282] – Turbomachinery – Thermodynamics of energy conversion ;

•[BM 4 283]...