Large Eddy Simulation of Turbulent Reactive Flow

Abstract

The wide range of temporal scales involved in the turbulent reactive flow brings great requirements to the numerical simulation processes. The modeling of reactive flows with multi-step detailed chemical kinetics calls for the small enough time step size, which will result directly in a huge computational cost. Different from the fixed time step methods adopted in most numerical simulations of the turbulent reactive flow currently, a method of self-adaptive time step is developed in this paper, in which the size of the time step in computation is automatically determined according to the time scales of both the chemical reaction and the turbulent fluctuation. Thus, compared with the fixed, very small time step throughout the whole calculation, the current self-adaptive time step method can reduce computational expense greatly. In order to validate this method, large eddy simulations of a methane-air turbulent reactive planar jet flow is carried out in this paper with the self-adaptive time step method. The mechanism of a simplified 4-step chemical kinetics is applied for the methane-air reaction. The dynamic model is adopted for the turbulent motion of sub-grid scale. The dynamic similarity model is used as the SGS model for the reaction rate. The LES results with the self-adaptive time step method depict satisfactorily the ignition process of the turbulent jet flame and give clear and detailed coherent structures of the fully developed turbulent reactive jet flow. The self-adaptive time step method helps to match the balance between saving computational efforts and catching more flow details.