Relevance of Computation Methods in Combustion to the Development of Turboreactor Furnaces

Summary

Developments in turboreactor cycles, the need to conform to pollution standards, the improvement in manoevrability life, and the reduction in the size and mass of combustion chambers have lead to increasingly expensive partial tests.

This is why engine designers have worked out computational methods for sizing and optimising the various elements with a limited number of tests, and for extrapolating the results obtained into the whole sphere of flights (Plate 1).

As regards combustion the physical phenomena at work are particularly complex: the flow is compressible, turbulent and recirculating, and in most cases purely three-dimensional; the local richness of the air-fuel mixture is very variable in the furnace, and the chemical reactions which bring many molecular species into play have very different speeds. Diphase phenomena (the atomization and vaporization of the fuel) cannot be overlooked. Moreover, the considerable interaction between turbulent and chemical kinetics is poorly understood from the fundamental point of view (plate 2).

In spite of these difficulties, manufacturers and SNECMA in particular have perfected computational methods which are now operational dimensioning tools. The relevance of these tools is illustrated by the three examples of methods presented below.