Effects of Chemical Reaction on Two-Dimensional Turbulence

Abstract

Direct numerical simulations of compressible two-dimensional homogeneous turbulent reacting flows are conducted to investigate the interactions between turbulence and chemical reaction. Both isothermal and exothermic nonpremixed reactions are considered. In isothermal reacting simulations, the turbulence is not affected by the reaction and is characterized by the large scale coherent vortices and vorticity-gradient sheet structures. The spatial structures of the density and temperature fields are similar to that of vorticity. However, mixing and reaction occur in the layer like (lamellar) structures which are mainly formed in the hyperbolic flow regions, where the vorticily-gradient sheets are present and the turbulent stretching dominates the circulation. Analysis of the simulations with exothermic reactions indicates that the heat of reaction has significant influence on thc spatial and the compositional structure of velocity, scalar and thermodynamic variables. The fluctuations of the density, the temperature, the pressure and the dilatation are substantially increased due to nonuniform heat release. The heat of reaction also modifies the small scale solenoidal velocity field. At early times, when the reaction is significant, the magnitude of the vorticity (enstrophy) is enhanced by the baroclinic vorticity generation. At late times, when the reaction is almost completed, the molecular dissipation is dominant and the magnitude of vorticity decays continuously. Examination of the energy transfer among the rotational and the compressive components of the kinetic energy and the internal energy indicates that the energy of reaction is transfered to the compressive component of the kinetic energy by the pressure-dilatation correlations. The turbulent advection then transfer the energy from the compressive component of the kinetic energy to its rotational component.