Turbulent high-pressure reaction-rate modeling using the Double-conditioned Conditional Source-term Estimation method

Abstract

An evaluation of the submodels constituting the Double-Conditioned Source-term Estimation (DCSE) method for utilization in Large Eddy Simulation (LES) is presented which makes use of a single realization of a turbulent high-pressure reactive-flow database obtained from Direct Numerical Simulation (DNS). A filtered and coarsened DNS (FCDNS) field is first created to mimic a real LES field, and the FCDNS values for thermodynamic variables (temperature, density and species mass fractions) are used as inputs to the DCSE model to predict the FCDNS reaction rates. It is found that there are significant errors in the predictions of the filtered reaction rate compared to the template. These errors are attributed to important aspects of the model, some of which are discussed here, namely, the integral inversion necessary to find the conditional-filtered values of the thermodynamic variables and the modelling of the joint probability density function of the conditioning variables, the latter being by far the largest source of error. Assuming a β-PDF for the marginal PDF of the reaction progress variable is shown to be a particularly poor choice, as is the assumption that the conditioning variables are statistically independent.