Spontaneous Transition of Turbulent Flames to Detonations in Unconfined Media

TL;DR

This paper demonstrates through direct numerical simulations that unconfined, turbulent, premixed flames can spontaneously transition to detonations at high turbulent intensities, revealing a new instability mechanism distinct from traditional models.

Contribution

It introduces a novel mechanism for DDT in unconfined media, showing that high turbulence can inherently cause flames to become unstable and transition to detonation without confinement.

Findings

Unconfined turbulent flames can undergo DDT at high turbulence levels.

The transition mechanism differs from traditional spontaneous reaction wave models.

Predicted critical flame speeds match DNS results.

Abstract

Deflagration-to-detonation transition (DDT) can occur in environments ranging from experimental and industrial systems to astrophysical thermonuclear (type Ia) supernovae explosions. Substantial progress has been made in explaining the nature of DDT in confined systems with walls, internal obstacles, or pre-existing shocks. It remains unclear, however, whether DDT can occur in unconfined media. Here we use direct numerical simulations (DNS) to show that for high enough turbulent intensities unconfined, subsonic, premixed, turbulent flames are inherently unstable to DDT. The associated mechanism, based on the nonsteady evolution of flames faster than the Chapman-Jouguet deflagrations, is qualitatively different from the traditionally suggested spontaneous reaction wave model, and thus does not require the formation of distributed flames. Critical turbulent flame speeds, predicted by this mechanism for the onset of DDT, are in agreement with DNS results.