A spectral model for the sound pressure from turbulent premixed combustion

We present a model for the spectral distribution of heat release in turbulent premixed combustion and show how it can be applied to the calculation of sound pressure. Experimental data are presented from premixed swirling jet flames at three thermal powers, three equivalence ratios and for a variation of the fuel composition. A simultaneous PIV-LIF technique was used to determine the spatial spectra of the progress variable variance and turbulence kinetic energy. It was found that the spectra of progress variable correspond well with model spectra derived for homogeneous turbulence. Mapping these Eulerian spatial spectra to Lagrangian time spectra, we show how the integral frequency spectrum of heat release fluctuation can be computed using local values of time averaged heat release rate density, turbulence kinetic energy and turbulence lengthscale. With these the spectral distribution of sound pressure from turbulent premixed combustion is calculated and compared with measured sound pressure spectra. Very good quantitative agreement is obtained in all cases.