Influence of Turbulent Fluctuations on Detonation Propagation

TL;DR

This study investigates how turbulent fluctuations influence detonation propagation, combining experiments and advanced simulations to understand the reaction zone structure, burning mechanisms, and the role of turbulence in unstable detonations.

Contribution

It introduces a novel Large Eddy Simulation method extended for shock and rapid transient flows, providing detailed insights into turbulence effects on detonation dynamics.

Findings

Turbulent fluctuations significantly enhance burning rates.

Power-law distribution of shock PDFs with exponent -3 was observed.

Simulations accurately captured cellular detonation structures.

Abstract

The present study addresses the reaction zone structure and burning mechanism of unstable detonations. Experiments investigated mainly two-dimensional methane-oxygen cellular detonations in a thin channel geometry. The sufficiently high temporal resolution permitted to determine the PDF of the shock distribution, a power-law with an exponent of -3, and the burning rate of unreacted pockets from their edges - through surface turbulent flames with a speed approximately 3-7 times larger than the laminar one at the local conditions. Numerical simulations were performed using a novel Large Eddy Simulation method where the reactions due to both auto-ignition and turbulent transport and treated exactly at the sub-grid scale in a reaction-diffusion formulation. The model is an extension of Kerstein & Menon's Linear Eddy Model for Large Eddy Simulation to treat flows with shock waves and rapid gasdynamic transients. The two-dimensional simulations recovered well the amplification of the laminar flame speed owing to the turbulence generated mainly by the shear layers originating from the triple points and subsequent Richtmyer-Meshkov instability associated with the internal pressure waves. The simulations clarified how the level of turbulence generated controlled the burning rate of the pockets, the hydrodynamic thickness of the wave, the cellular structure and its distribution. Three-dimensional simulations were found in general good agreement with the two-dimensional ones, in that the sub-grid scale model captured the ensuing turbulent burning once the scales associated with the cellular dynamics, where turbulent kinetic energy is injected, are well resolved.