Turbulence characteristics within the local reaction one of a high-intensity turbulent premixed flame

Abstract

An attempt has been made to measure the Kolmogorov scale of turbulence within the local reaction zone of a turbulent premixed flame established in a regime in which the Kolmogorov scale of turbulence in the nonreacting flow is smaller than the laminar premixed flame thickness. In orde to measure the Kolmogorov scale of turbulence within the local reaction zone, the specially arranged diagnostics composed of an laser-doppler velocimeter (LDV) system and a microelectrostatic probe have been adopted. By using this technique, the velocity fluctuation within the local reaction zone can be successfully distinguished from that in unburned mixture or burned gas stream. Thus, the Kolmogorov scale of tubulence in the local reaction zone could be evaluated on the basis of the power spectrum density function derived from the velocity fluctuations. The power spectrum density function, the turbulence intensity, and the Kolmogorov scale of turbulence derived from velocity fluctuations in the approach flow are shown to be the same as those in the nonreacting flow. Also, small-scale eddies in the nonreacting flow, which are smaller than the laminar premixed flame thickness, are confirmed to exist in the approach flow. It is found that the approach flow turbulence increase in the local reactionzone because of the expansion of gases due to heat release. The Kolmogorov scale of turbulence derived from velocity fluctuations in the local reaction zone is shown to be much larger than the laminar premixed flame thickness. This result implies that the small-scale eddies in the approach flow may not survive through the preheat zone.