The influence of turbulence on the rate of chemical reactions


Аuthors

Molchanov A. M.*, Yanyshev D. S.**, Tushkanov A. S.

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: alexmol_2000@mail.ru
**e-mail: dyanishev@gmail.com

Abstract

A model of chemically nonequilibrium turbulent combustion has been developed, taking into account the effect of turbulent temperature and concentration fluctuations on the intensity of chemical reactions. A turbulence model for high­speed flows is proposed. The averaged rate of chemical reactions depends not only on the average values of the gas­dynamic parameters, but also on the pulsations of these quantities. The presence of correlations between temperature fluctuations and concentrations leads to the fact that the speed of the process can both increase and decrease. In the procedure of mathematical description of a complex of chemical reactions, an approach was used based on the probability density distribution function (PDF), which depends on a number of gas­dynamic parameters that are considered as random variables in a turbulent flow. To determine the PDF, we used a model based on the representation of this function in the form of a predetermined form. This function is presented as a product of 3 independent functions of a predetermined form (delta functions for density, Gauss distribution for temperature and multidimensional beta function for concentrations) followed by solving equations describing the parameters of these functions. It is shown that taking into account the effect of turbulence on the rates of chemical reactions is very important for determining the moment of ignition of a gas mixture in chemically nonequilibrium flows (Damköler number is within 0.01 <Da <100). With the developed burning this influence is insignificant. Also, turbulent pulsations have a significant effect on the moment of burnout failure in the jets of aircraft engines with increasing flight altitude. The obtained calculated results are in satisfactory agreement with the experimental data.

Keywords:

turbulence, chemical kinetics, probability density distribution function, averaged flow parameters, dispersion of temperature and concentrations

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