Combustor Modelling - A Maturing State of the Art

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between the turbulence field and the reaction rate is generally treated by ad-hoc expressions lacking rigorous formulations. Specifically, the use of eddy break up model in this study to model flame-turbulence interaction needs to be critically assessed. It should be emphasized that the eddy break-up expression falls short of a probabilistic description for the temporal variation of the turbulence energy and dissipation, i.e., the delay time associated with the break-up of eddies to provide adequate interfaces with the hot gas, as a consequence of the processes initiated by the turbulence energy, seems to have been neglected. A cross-correlation analysis might be profitably adopted for this purpose. The local Reynolds number insensitivity of the model together with the fixed eddy states presumed in the derivation are also recognized as serious shortcomings. However, the latter influence can probably be accounted for by reference to a differential equation which has as the dependent variable the mean square fluctuation equation along with a particular waveform for the instantaneous variation of the composite mass fraction. Incorporation of radiation effects in a reacting environment presents additional problems. These concern the nature of the fundamental mathematical formulation (classical equations are integro-differetial) and the resulting severe computational limitations imposed by current computers in adequately resolving a practical radiation field without prior knowledge of the flow field. Furthermore, information about the field distribution of absorption and scattering coefficients is rarely available. Problems also remain in the mathematical treatment of multi-phase flow aspects and the detailed local representation of the various exchange processes between phases in a reacting flow. Specific modelling issues here 14