Broetz, W.; Schönbucher, Axel; Banhardt, V.; Schiess, N.:

Periodic and statistical properties of coherent short-time structures in pool flames.

In: Berichte der Bunsen-Gesellschaft, Jg. 87 (1983) ; Nr. 11, S. 997-1004
ISSN: 0005-9021
Zeitschriftenaufsatz / Fach: Chemie
Coherent structures of pool flames are visualized by synchronous holog. interferometry. There are large coherent structures which have periodical properties and small coherent structures both with periodical and statistical properties. The periodical phenomena can be classified into 3 types of instabilities. The 1st type is a low-frequency instability with frequencies of the order of 12 Hz (for a n-hexane [110-54-3] pool flame, d = 4.6 cm) and depends considerably on the pool diam. The 2nd and 3rd types have frequencies in the order of 300 Hz and 500 Hz, which depend mainly on the fuel type. The statistical properties of the small coherent structures indicate that the turbulent exchange coeffs. for heat and matter have values 6 times as large as the exchange coeffs. for the momentum. The turbulent Prandtl, Schmidt, and Lewis nos. are functions of the distance from the fuel surface and vary between the following limits: 0.16 ? Prt ? 0.35, 0.19 ? Sct ? 0.35, and 0.74 ? Let ? 1.29, resp.