Prediction of the Sound Radiated from Open Flames by Coupling a Large Eddy Simulation and a Kirchhoff-Method

Hybrid methods, coupling CFD codes and acoustic methods like the acoustic analogy, the linearised Euler equations and the Kirchhoff-Method are being used to predict the sound produced by turbulent combustion, since the present computational power only allows an accurate estimation of the physical quantities, in a reasonable computational time, near the source. This means that the acoustic far field cannot be determined by a direct simulation. This research attempts to show that the Equivalent Source Method (ESM) and the Boundary Element Method (BEM), which are considered as Kirchhoff-Methods, can also be used to determine the sound generated by combustion. These two methods have the advantage that only one acoustic variable must be known at a surface surrounding the source zone and that the far field can be directly computed. The sound power generated from two open diffusion flames have been calculated with both the ESM and the BEM, using the velocity distribution over cylindrical control surfaces computed with a Large Eddy Simulation. Results of the calculations are presented and compared with the measured sound power of the same flames. For one configuration good agreement between measurement and simulation at low and middle frequencies is obtained. Possible reasons for the differences for the other configuration will be discussed.