Flow Mechanisms and Diffusion Combustion of Turbulent Jets
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Flow Mechanisms and Diffusion Combustion of Turbulent Jets V. P. Vorotilin Institute of Applied Mechanics, Russian Academy of Sciences, Moscow, 125040 Russia e-mail: [email protected] Received August 25, 2017
Abstract—The problem of flow and combustion of turbulent jets of fuel gas in the external medium of an oxidant (air) is solved with regard to the existence of the actual boundary of the turbulent flow region of a jet. Based on the ideas of the friction force of the external flow acting on the boundary of a jet, the entrainment equation for the external medium is derived that closes the system of equations of motion of turbulent jets. The physical meaning of the dissipation rate of the turbulent energy of a jet is interpreted as the work of the friction force. To describe the combustion kinetics, the limit of instantaneous reactions corresponding to the diffusion combustion mode is used. Calculations of the effective reaction rates for reactants and the volumes occupied by them are based on the representation of a turbulent medium as an aggregation of independent turbulent particles—vortices—whose random contacts lead to the mixing and combustion of reacting substances [31]. The concomitant phenomena of flow and combustion are analyzed, including radiation effects. In particular, it is shown that the apparent increase in the combustion temperature with increasing Reynolds number is in fact attributed to the relative decrease of thermal radiation losses. Qualitative agreement is obtained between the results of the theoretical calculations of the length of a combustion torch and experimental data. DOI: 10.1134/S1063776118010193
1. INTRODUCTION By an example of the simplest variant of a straight turbulent jet in a parallel flow of the surrounding oxidant medium, air, the general problem of the flow and diffusion combustion of a turbulent jet of fuel gas is considered. Formally, this problem is completely solved on the basis of the equations of hydrodynamics and convective diffusion with chemical reaction. However, in view of the extreme complexity of the turbulent flow patterns, it is impossible to obtain exact analytic or approximate solutions to these equations. The computation models available are based on semiempirical methods for describing transfer and reaction processes in turbulent flows, including the models involving conserved scalar methods and reagent concentration distribution functions [1–11]. From the theoretical viewpoint, the search for new solutions has been motivated by the absence of the concept of the actually existing interface between a turbulent jet and a region of laminar flow in the external medium in the above-mentioned computation models. The presence of clearly distinguishable, irregular (in length), and pulsating (in time) interface between the turbulent flow region in the jet and the laminar flow in the external medium is a distinctive feature of the flow of turbulent jets. It is this interface where the fuel of the jet and the oxidant o
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