Radiation of noise in turbulent non-premixed flames

A model for the prediction of combustion-generated noise in non-premixed flames has been developed. This model is based on Lighthill's acoustic analogy and employs the flamelet/progress variable model to express the excess density as function of mixture fraction and reaction progress variable. In this model, three major sources of sound have been identified, and their individual contribution to the acoustic spectra and overall sound pressure level are analyzed for a nitrogen-diluted methane-hydrogen/air flame. The hybrid approach, combining a large-eddy simulation and a computational aeroacoustic method, introduces spurious noise which can pollute the acoustic results. All relevant sources of spurious noise are analyzed, and a physics-based low-pass filter is proposed which eliminates spurious noise due to the convection of acoustic sources. The numerical predictions for both statistical flow field quantities and acoustic results have been validated with experimental data. The good agreement between experiments and simulation highlights the potential of the method for applications to more complex flow configurations and to provide further understanding of combustion noise mechanisms.