On combustion generated noise

Abstract

Upon review of past experimental results and theoretical efforts it is apparent that the mechanism by which combustion noise is generated is not well understood. A theory of combustion noise is developed in this paper which follows rigorously from the principles of fluid mechanics. Lighthill's approach, used in his studies of aerodynamic noise, is closely followed in the present work. The sound radiated from open, turbulent flames is found to depend strongly upon the structure of such flames; at present their structure is not well known. However, meaningful bounds and scaling rules for the sound power output and spectral content are derived based upon the present limited knowledge. A framework is developed which explains past experimental work and the origin of combustion noise.

Spectral Separation of the Turbofan Engine Coherent Combustion Noise Component

“…Bendat and Piersol (1966, 1971 39-41 discuss these methods. Among the methods discussed is one using coherent output power spectra for noise source identification.…”

“…13 Strahle (1971) 14 developed a framework that explained past experimental studies of direct combustion generated noise from flames using an approach similar to the one Lighthill (1952Lighthill ( , 1954 15,16 used in his studies of aerodynamic noise. Further developments in scaling laws were derived by Strahle (1972Strahle ( , 1975 17, 18 involving the first Eulerian time derivative of the chemical reaction rate integrated over the reacting volume.…”

On the thermo-acoustic Fant equation

“…Trapped sound waves produced by a flame which are localised near the source and confined within a gas turbine, afterburner, furnace or other thermofluid device involve pressure fluctuations whose interaction with the flame modulates the heat release by changing the fuel burn rate. Large amplitude 'combustion instabilities' arise from this back-reaction when pressure and heat release are appropriately phased [1][2][3][4][5][6][7][8][9][10]. These instabilities are a significant source of structural fatigue and noise radiated into the environment.…”

Theory of Combustion Noise

“…Another approach to the problem was taken by Strahle [9] who adopted Lighthill's formalism for a noise field prediction. The first decisively important factor was the overall description of the turbulent flame to be used for the evaluation of the volume integral expressing the monopole sound field.…”