An Unsteady/Flamelet Progress Variable Method for LES of Nonpremixed Turbulent Combustion

An unsteady flamelet/progress variable model has been developed and formulated as an extension of the steady flamelet/progress variable model. For this model, a large number of unsteady laminar flamelet simulations is performed for various conditions, and solutions are recorded as function of time. From this, a flamelet library is generated, which provides the filtered quantities of all scalar values as function of the filtered mixture fraction, the mixture fraction sub-filter variance, the filtered reaction progress variable, and the filtered scalar dissipation rate. The model has been implemented in an LES code. Simulations have been performed for a confined swirl burner using the unsteady flamelet/progress variable model. The results are compared with experimental data for velocities and velocity fluctuations, temperature, CO2, and CO mole fractions. The results agree reasonably well with the experiments for all quantities. In particular, CO is predicted with good accuracy.