Large Eddy Structures in Transitional and Turbulent Flames.
Final rept. 1 Jul 82-30 Jun 85,
CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF MECHANICAL ENGINEERING
Pagination or Media Count:
An experimental investigation of transitional and turbulent jet diffusion flames was carried out with emphasis on the derivation of time-dependent information from measurements of various fluctuating quantities in these flames. Special efforts were made to control carefully, and vary systematically, the initial and boundary conditions of each flame. Mapping of the signal reveals that the inner flame boundary moves radially outward in the near flow-field xD10 to xD40 and later converges toward the flame axis. Meanwhile, the outer flame boundary grows steadily with downstream axial distance, indicating a consistently widening reaction zone, for the entire area examined xD10 to xD60. Profiles of RMS values of ion current were correlated with flame boundary locations. A double peak pattern was found in the RMS profiles, each peak coinciding with the large gradients of the mean ion current profiles. Near the inner flame boundary, the flame front fluctuates across the probes sampling volume, generating largely fluctuating components of ion current. In the central flame region, the probe experiences a more continuous flame presence and less fluctuations. This causes the mean ion current signal to remain high while the RMS signal drops off rather rapidly. As the outer flame boundary is approached, an increase in fluctuations again takes place.
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