Characteristics of chemically reacting compressible homogeneous turbulence

Direct numerical simulations (DNS) are conducted to study the turbulence-ch emical reaction interactions in homogeneous decaying compressible fluid flo ws. The reaction is of a single-step irreversible Arrhenius type. The resul ts indicate that the heat of reaction has a noticeable influence on the sol enoidal and the dilatational turbulent motions. The effect of reaction on t he solenoidal velocity field is primarily due to variation of the molecular diffusivity coefficients with temperature and appears at small scales. How ever, the dilatational motions are affected more than the solenoidal motion s and are intensified at all length scales. The decay rate of the turbulent kinetic energy is dependent on the molecular dissipation and the pressure- dilation correlation. In isothermal reacting cases, the net contribution of the pressure-dilatation is small and the turbulent energy decays continuou sly due to viscous dissipation. In the exothermic reacting cases, the press ure-dilatation tends to increase the turbulent kinetic energy when the reac tion is significant. Analysis of the flow structure indicates that the flow is dominated by strain in the reaction zones. Also, consistent with previo us studies, the scalar gradient tends to align with the most compressive st rain eigenvector and the vorticity vector tends to align with the intermedi ate strain eigenvector. The heat of reaction weakens this preferential alig nment, primarily due to variation in molecular transport coefficients. The spatial and the compositional structure of the flame are also affected by t he modification of the turbulence and the molecular coefficients. (C) 2000 American Institute of Physics. [S1070-6631(00)00205-1].