Abstract:
Fractal analysis is undertaken to characterize flame surface fluctuations on an unconfined turbulent premixed flame and the resulting far-field acoustics fluctuations. Results
indicate that combustion noise is monofractal and is characterized by an anticorrelated
structure with a Hurst exponent less than 0.5. The anticorrelated nature was identified in
the pressure fluctuations as well as flame surface fluctuations for small time-scales. Additionally, results suggest that flame surface fluctuations are multifractal for large time
scales. The calculated Hurst exponent increases noticeably with the equivalence ratio
and decreases slightly with Reynolds number for the investigated operating conditions.
Variation in the Hurst exponent for combustion noise data is compared with a case study
of synthetic fluctuations comprised of linear combinations of white and 1/f2 noise. These
results provide a more detailed characterization of the temporal structure of flame surface fluctuations and resulting noise emission from turbulent premixed flames than is
presently known.
