Winkler A., Wäsle J., Hirsch C., Sattelmayer T.

An experimental investigation of the noise emission of turbulent premixed flames is presented. It is found that the acoustic spectra always show the same behaviour in principle: The noise emission peaks at some peak frequency fpeak, while in the low frequency range the acoustic data show a power law dependence upon frequency with a positive exponent. In contrary, the high frequency range is characterized by a negative exponent. Most authors agree that the peak emission occurs near a frequency, which can be calculated from proposing the Strouhal number being equal to unity. For calculating the Strouhal number, different characteristic length and velocity scales were taken in the past, favouring either turbulence or chemical kinetics influence. However, most data of these publications suffer from the absence of measurement techniques with spatial resolution. As a result, these findings might be interesting with respect to the investigated burner type, while it is impossible to draft universal rules for the scaling of the peak frequency. This originates from the fact that the interaction between turbulence and chemical kinetics is at most covered by global parameters, while details of the turbulent flow are not considered. Consequently, the presented paper determines the peak frequency from a characteristic time scale, which includes both, the local turbulence and the chemical kinetics. The desired time scale is deducted from the local turbulent flame speed and the flame brush thickness. Both will be calculated using a combustion model, which requires the turbulence length scale as well as velocity fluctuations. These data are acquired using a PIV-System. Finally, the peak frequency calculated with the PIV data is compared to acoustic data. The final paper will communicate our state of the work.