Gas turbine cooling. Combustion chamber

The design of a combustion chamber liner must take into account the problem of cooling, which is a fundamental element in TAG gas turbine design studies. In the past, cooling of this component was facilitated by low maximum temperatures and high air availability. Higher temperatures and the need to reduce pollutant emissions mean that much more stringent criteria have to be met, of the same type as those found in blades and nozzles. However, unlike these latter components, the development of cooling for the walls of the CC combustion chamber requires a more in-depth study, due to the problem of radiation.

The wall of a combustion chamber is a very critical element in modern gas turbines, as it is exposed to high convective and radiative heat flows, which increase during engine start-up and shut-down phases. The main aspects of wall cooling system studies are conditioned by the need to reconcile the requirements of cooling, combustion efficiency and stability, and pollutant reduction, the latter often involving so-called lean primary zones with less air available for wall cooling.

While the geometrical characteristics of the wall are comparable to those of a flat surface, which implies obvious simplifications compared to the case of blades, the determination of the heat flux to which the wall is exposed is, on the contrary, highly complex. The presence of radiation, which depends on the emission capacity of the burnt gases and that of the particles (liquid fuels), complicates the determination of the heat flux on the wall. In addition, the movement of gases in the combustion chamber is deliberately complex, three-dimensional and highly turbulent, to help stabilize the flame, level out temperature peaks and limit pollutant emissions.

This dossier is part of a series on "Gas turbine cooling":

• BM 4565 "Influence on yield" ;

• BM 4566 "Techniques and efficiency" ;

• BM 4567 "Combustion chamber".