A USM turbulence-chemistry model for simulating NOx formation in turbulent combustion

A unified second-order moment (USM) turbulence-chemistry model for simulating NOx formation in turbulent combustion is proposed. All the correlations, including the correlation of the reaction-rate coefficient fluctuation with the concentration fluctuation, are closed by the transport equations in the same form. This model abandons the series expansion approximation of the exponential term or the approximation of using a product of two single-variable PDFs instead of a joint PDF. The proposed model is used to simulate methane–air jet diffusion combustion and NOx formation. The combustion prediction results are compared with those using the EBU-Arrhenius model and other two versions of the second-order moment model. The NOx prediction results are compared with those using the pure presumed PDF model. Validation of predictions using the experimental data given by the Sandia National Laboratory, USA indicates that the proposed model gives better results than other models, and it is much economical than other refined models.