Higher-order projection method for the simulation of unsteady turbulent nonpremixed combustion in an industrial burner

摘要

The modeling of transient effects in burners is becoming increasingly important. The problem of ensuring the safe performance of an industrial burner, for example, is much more difficult during the startup or shutdown phases of operation. The peak formation of pollutants is also much more dependent on transient behavior, in particular, on peak temperatures, than on average operating conditions. In this paper we present a new methodology for the modeling of unsteady, nonpremixed, reacting flow in industrial burners. The algorithm uses a second-order projection method for unsteady, low-Mach number reacting flow and accounts for species diffusion, convective and radiative heat transfer, viscous transport, turbulence, and chemical kinetics. The time step used by the method is restricted solely by an advective CFL condition. The methodology is applicable only in the low-Mach number regime (M < .3), typically met in industrial burners. The projection method for low-Mach number reacting flow is an extension of a higher-order projection method for incompressible flow (9, 5, 3,4) to the low-Mach number equations of reacting flow. Our method is based on an approximate projection formulation. Radiative transport is modeled using the discrete ordinates method. The main goal of this work is to introduce and investigate the simulation of burners using a higher-order projection method for low-Mach number combustion. As such, the methodology is applied here only to axisymmetric flow in gas-fired burners for which the boundaries can be aligned with a rectangular grid. The perfect gas law is also assumed. In addition, we use a one-step reduced kinetics mechanism, a kappa (-) epsilon model for turbulent transport, and a simple turbulent combustion model.