A Combustion Model Based On MMC And REDIM Technologies

Probability density function(PDF) combustion model can be used to calculate the premixed, non-premixed and partial premixed turbulent combustion. A micro mixing model, however, is needed to solve the PDF transport equation. Most of the currently available micro mixing models are faced with this or that problem. Multiple mapping conditioning(MMC) approach is a new micro mixing model, combining the features of the conditioning moment closure and mapping closure. It first selects the particles to form particle pairs, conditioned on one or multiple reference variables,then mixing these particle pairs. In theory, MMC model satisfies all the six required properties of micro mixing model. On the other hand, reaction-diffusion manifold(REDIM) is a method for reducing the detailed reaction mechanism. It takes into account the coupling of reaction and molecular transport processes explicitly, and therefore it is capable of describing fast reaction regions as well as regions where chemical kinetics are slow and diffusion governs the overall process.Based on the recently developed MMC method for micro mixing and the REDIM technology for mechanism reducing, a new combustion model called MMC-REDIM, is proposed in the present work, which integrates the ‘multiple dimensional’ manifold of REDIM with the ‘multiple dimensional’ mapping of MMC.The new combustion model is then applied to the hybrid finite volume-Lagrangian particle method. The flow field is obtained by solving the Euler flow field equations with finite volume method, and the information is then conveyed to Lagrangian particles to control their movement in physical and composition space. At the same time, the statistical information, such as density, source term, etc., are collected from particles and transferred to finite volume approach for updating the Euler flow field.For avoiding the numerical instability problem caused by strong density coupling of Euler flow field and Lagrangian particle field, the ‘equivalent enthalpy’ and the‘density correction’ methods are used.In order to quantitatively analyze the performance of the new model, theMMC-REDIM model and the hybrid finite volume-Lagrangian particle method are implemented into the LESOCC2 C code, and then employed to calculate a one-dimensional premixed laminar flame. The comparison of the flame propagation velocity, temperature, mass fraction of CO2, density, ‘equivalent enthalpy’ and so on,between the MMC-REDIM calculation and direct numerical simulation(DNS)calculation shows a good overall agreement, which demonstrates the capability of MMC-REDIM model for describing the propagating of laminar premixed flame. It also indicates that the strong density coupling between Euler flow field and Lagrangian particle field cannot be tackled accurately by solely using the ‘equivalent enthalpy’ method. The additional ‘density correction’ algorithm is necessary.It is worth pointing out that the goal of proposing MMC-REDIM model is to develop a good performance sub-grid scale combustion model in large eddy simulation(LES) framework. Although its performance is only verified by a calculation of laminar flame in the present work, it can be in theory extended to conduct LES of turbulent flame.