Noise calculation in a turbulent non-premixed flame using a hybrid analytical-LES method

In the present work, the noise of a turbulent non-premixed free flame is calculated. A Hybrid method with Lighthill analogy along with a CFD simulation is used to evaluate combustion noise. In this way, the reactive flow equations are solved by the Large Eddy Simulation and Partially Stirred Reactor model to simulate the interaction of turbulence and reaction. Then the combustion noise source terms including heat release fluctuation and non-isomolar combustion are extracted and used as the sources of Lighthill analogy. The assumption of compact flame is applied to the Lighthill equation and the Green function is used to calculate far field pressure fluctuations. It was shown that in low and medium frequency sound pressure level is in a good agreement with experimental data. By the way at the high frequencies the pressure level does not follow the experimental data. This discrepancy can be related to the compact flame assumption used in analytical solution. The results show that this analytical method can produce acceptable results with a low computational cost. Also, the noise emitted by the non-isomolar fluctuations is negligible against that of heat release fluctuations and can be ignored.