Theory of combustion noise

Abstract A unified theory of noise generation and amplification by turbulent combustion of premixed fuel and liquid fuel droplets, has been developed within the framework of the fluid mechanics of the reacting gas. The overall sound generation processes have been classified in terms of the sound due to an isolated turbulent flame and that due to the interaction of a flame with its environment in a typical combustor. The analysis has been focused on, (i) the far field noise characteristics, and (ii) the mechanism of sound generation, dispersion, and transmission in the vicinity of an open flame. The acoustic intensity generated by a turbulent premixed flame is found to be a function of the relevant aerothermochemical parameters and the flame structural factor, expressed in terms of six double correlation functions characterizing the flame structure. Explicit expressions for the sound intensities are obtained based on a wrinkled flame model and a distributed reaction model. Noise generated by liquid droplets are classified in terms of intrinsic and turbulent driven noise components. Analysis of ducted combustion systems reveals that resonant oscillations occur with resulting noise intensities far greater than from the corresponding open flame. Calculated sound intensity spectra are in good agreement with experimental data.