Small-scale intermittency of premixed turbulent flames

TL;DR

This paper experimentally investigates the small-scale intermittency of premixed turbulent flames, revealing inner intermittency characterized by high-curvature structures, which has implications for modeling flame behavior.

Contribution

It is the first to distinguish and analyze the small-scale inner intermittency of premixed turbulent flames through experimental measurements.

Findings

Frequency spectrum exhibits a -2 power-law subrange consistent with Kolmogorov theory.

Moments of flame position increments scale anomalously with saturation at higher orders.

High-curvature cusp-like structures on the flame surface are identified as the origin of small-scale intermittency.

Abstract

Premixed turbulent flames, encountered in power generation and propulsion engines, are an archetype of a randomly advected, self-propagating surface. While such a flame is known to exhibit large-scale intermittent flapping, the possible intermittency of its small-scale fluctuations has been largely disregarded. Here, we experimentally reveal the inner intermittency of a premixed turbulent V-flame, while clearly distinguishing this small-scale feature from large-scale outer intermittency. From temporal measurements of the fluctuations of the flame, we find a frequency spectrum that has a power-law subrange with an exponent close to $-2$, which is shown to follow from Kolmogorov phenomenology. Crucially, however, the moments of the temporal increment of the flame position are found to scale anomalously, with exponents that saturate at higher-orders. This signature of small-scale inner intermittency is shown to originate from high-curvature, cusp-like structures on the flame surface, which have significance for modeling the heat release rate and other key properties of premixed turbulent flames.