Intermittency of inter-scale kinetic energy transfer and of energy exchange between internal and kinetic energy in turbulent premixed flames

TL;DR

This study investigates the highly intermittent and skewed nature of inter-scale kinetic energy transfer and heat exchange in turbulent premixed flames using direct numerical simulation data.

Contribution

It provides the first detailed analysis of intermittency in energy transfer and heat exchange in premixed flames, highlighting their extreme fluctuations and statistical characteristics.

Findings

Intermittency is highly significant with long-tailed, skewed PDFs.

Energy transfer and heat exchange exhibit large kurtosis, indicating extreme fluctuations.

Results emphasize the importance of considering intermittency in modeling turbulent flames.

Abstract

Inter-scale kinetic energy transfer in turbulent flows is accompanied by very intense and intermittent spatial-temporal fluctuations. Such intermittency is expected to be particularly prominent in premixed flames, where heat release, density variations, dilatation, and chemical reactions are localized to spatial scales that are substantially smaller than scales of large turbulent eddies but are often larger than or comparable with Kolmogorov length scale. Nevertheless, intermittency of inter-scale energy transfer and of heat exchange between internal and kinetic energy in premixed flames has not yet been given due attention. The present work aims at bridging this knowledge gap. For this purpose, three-dimensional direct numerical simulation data obtained earlier from a statistically stationary, planar, one-dimensional lean hydrogen-air flame propagating in moderately intense turbulence are filtered using cubes of various widths. Subsequently, Probability Density Functions (PDFs) of various instantaneous flow characteristics are sampled by processing the filtered fields of velocity, pressure, density, and their spatial gradients. The sampled PDFs exhibit long tails, are highly skewed, and are characterized by a large kurtosis, thus, evidencing significant intermittency of inter-scale energy transfer and heat exchange between internal and kinetic energy in the flame.