Experimental investigation and spectral modeling of turbulent combustion noise from premixed and non-premixed flames

The study at hand extends an existing theory of turbulent combustion noise for premixed flames towards the prediction of noise spectra from non-premixed flames. Based on a numerical simulation of the mean reactive flow field, the theoretical combustion noise model predicts the radiated noise spectra. An experimental campaign investigating the influence of flame operating parameters on the spectral noise emission from open natural gas swirl flames delivered reference data to validate the introduced model extensions accounting for the characteristics of noise emission from non-premixed flames. A novel experimental procedure for the quantification of fuel burnout of open premixed swirl flames under the influence of entrainment ensures comparability between numerical predictions and experimental data recorded from premixed and non-premixed flames. The results show, that thermal power output and mixture composition are the primary factors of influence governing combustion noise emission. These quantities are closely related to the thermal power density of the flame. Also, premixed and non-premixed flames possess similar noise emission characteristics when operated under similar flow and mixture conditions. Observed trends and amplitude levels can be correctly reproduced by the extended combustion noise model, which enables noise prediction using the developed numerical tool from time averaged simulation data. In a further step, the model was applied to a commercial marine heating unit. In combination with a simple numerical model of sound propagation inside the heater, the spectrum of the radiated noise was successfully predicted, demonstrating the applicability of the developed approach to typical problems of industrial development.