Thermal field structures in low Damkohler reacting flows

This paper is mainly concerned with the regime of distributed reaction zone s of a well-stirred reactor, where the Damkohler number is below unity. It is an original study compared with the majority of work done in the field o f the interaction between combustion and turbulence in premixed flames. The turbulent structures are subjected to opposing effects, i.e. reduction ind uced by chemical effects and expansion induced by the increase in mean temp erature due to exothermic reactions. When Da >1, the first effect due to th e chemistry can scarcely outweigh the expansion of the turbulent structures caused by the exothermic effect. This result is the major contribution of the present study. This phenomenon is not sufficiently known, both in terms of mechanism and quantitative effects. The first objective of this work is to try to provide a qualitative explanation, using an experimental and com putational analysis based on certain hypotheses. These assumptions will the n explain the difference observed between the behaviour of the temperature fluctuations in the case of reacting and non-reacting turbulent flow in low Damkohler number situations, where the exothermic effect is negligible. Th e present paper analyses and compares the fluctuating temperature structure s inside this reactor for various mean temperature situations. The experime ntal study is conducted using fine-wire thermoanemometry. The results of nu merical simulations obtained using the Navier-Stokes energy equations and t he chemical species transport equations associated with a turbulence model are compared with available measurements. The predictions were within engin eering accuracy of experimental data.