Periodische und statistische Eigenschaften kohärenter Kurzzeit‐Strukturen in Tankflammen

Abstract

Flammen / Holografische Synchroninterferometrie / Koharente Strukturen 1 Stromungs-Instabilitaten / Transporterscheinungen Coherent structures of pool flames are visualized by the synchronous holographic 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 three types of instabilities. The first type is a low-frequency instability with frequencies of the order of 12 Hz (for a n-hexan pool flame, d = 4.6 cm) and depends considerably on the pool diameter. The second and third 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 coefficients for heat and matter have values six times larger than the exchange coefficients for the momentum. The turbulent Prandtl numbers, Schmidt numbers and Lewis numbers are functions of the distance from the fuel surface. These functions vary between the following limits: 0.16 5 Pr, 5 0.35, 0.19 5 Sc, 0.35 and 0.74 Let 5 1.29.