Analysis of combustion noise of a turbulent premixed slot jet flame

Abstract

The sound generation due to the interaction between the turbulent flow field and a premixed slot flame is numerically studied by a hybrid analysis. The impact of varying gas expansion ratios and Markstein lengths is investigated. The acoustic flame response function and the acoustic source terms determine the overall flame response to heat release fluctuations. The location where sound is emitted is computed by the spatial and spectral acoustic source term distribution and a spectral flame front response study. The acoustic flame response of the slot jets is similar to that of round jets. From the current results and data from the literature it is suspected that as long as the flame undergoes a turbulent flame–flow interaction a typical acoustic pressure and heat release trend leads to an acoustic flame response trend of αSt2 in the low frequency region (St ≲ 20) and a plateau region βSt0 for St ≳ 20. In the energy containing region (αSt2), the acoustic sound is produced by local heat release fluctuations determined by the spectral flame front response at several mean flame front locations. The acoustic source terms depend on the gas expansion and shear layer effect induced by the flame front kinematics. At the flame base, flame pocket generation is enhanced at decreasing gas expansion ratio due to the increased vortex–flame interaction. At the flame tip, flame pocket generation is increased at high temperature ratios due to the hydrodynamic instability effect. The flame front kinematics affects the acoustic source terms by the flame–flow interaction and leads to a lower magnitude of flame response for decreasing gas expansion ratios.