Compressible fluid turbines - Losses and how to reduce them

In the "Design and operation" section of the "Compressible fluid turbines" article, we see that the overall efficiency of a turbine depends on :

• mechanical efficiency ;

• volumetric efficiency, a function of the flow rate q through the required clearance between stator and rotor ;

• of the adiabatic efficiency of the stage group, a function of the deceleration coefficients ϕ and ψ and the remaining velocity loss coefficient m.

We won't be looking at mechanical losses, which have a variety of origins. In this section, we will analyze the various phenomena that contribute to yield loss, and show how this loss can be limited. We have classified these yield losses into two categories.

Shortfalls represent available energy that cannot be transformed:

• of kinetic energy at the output of the last stage ;

• the energy of the leakage flow q, which will not produce any work.

The losses themselves, linked to flow, take the form of an increase in entropy and are represented essentially by the retardation coefficients ϕ and ψ and partially by the coefficient m (for losses between stages).