Self-similarity and small-scale intermittency in turbulent premixed flames

We reveal the presence of self-similarity and intermittency in the small-scale fluctuations of a turbulent premixed flame. From temporal measurements of the position of a methane-air V-flame, we find that the power spectrum has as a power-law dependence on frequency, over an intermediate range of time-scales, with a scaling exponent close to -2. This exponent is explained as a consequence of the flame fluctuating passively in response to perturbations from inertial-range turbulent eddies. Next, we calculate the moments of the temporal structure function, and find that they scale anomalously—a signature of small-scale intermittency—showing that higher frequency fluctuations have increasingly non-Gaussian, wide-tailed probability distributions. Our results have important implications for modelling turbulent flame speeds and heat release rate in premixed flames, while also showing how a flame reflects the characteristic features of the turbulent carrier flow.