Annihilation events topology and their generated sound in turbulent premixed flames

Abstract

This paper studies the contribution of flame annihilation events to the sound radiated by turbulent, premixed flames. Previously published direct numerical simulation (DNS) datasets of stoichiometric and lean (φ = 0.7) flames (Haghiri et al. 2018) are first examined using an efficient formulation of the method of Griffiths et al. (2015) to identify the annihilation events. Four classes of annihilation event are observed. Three of these -pocket burn-out, tunnel closure and tunnel formation -were defined by Griffiths et al. A 'multi-feature' event is also defined in this paper as any combination of the other three annihilation events occurring close enough such that their radiated sound can be considered as originating from a single event. Further post-processing of these stoichiometric and lean datasets shows that the fluctuations in heat release rate associated with these 4 observed types of annihilation events are responsible for the broadband sound radiated by both flames. This, in turn, suggests that flame annihilation is the physical mechanism by which air-fuel ratio affects the radiated sound amplitude at high frequencies. This result is supported by previous works which have shown that the sound radiated from individual annihilation events scales with the laminar flame speed and the temperature ratio.

Simulation of mild auto-ignition initiated by a hot spot

“…The remaining auto-ignitive flame and premixed flame continuously move towards each other until they meet and annihilate at t = t 5 . This event can be a significant source of sound, as also shown in other previous studies [1,4,17].…”

The impact of chemical modelling on turbulent premixed flame acoustics

“…A more detailed description of the method can be found in Brouzet et al. (2019). The DNS and a posteriori pressure traces and spectra are shown in figure 10.…”

“…2018; Brouzet et al. 2019). The focus is therefore placed on negative stretch values, when is dominant.…”

“…2013; Brouzet et al. 2019) or to establish scaling laws (Rajaram, Gray & Lieuwen 2006; Haghiri et al. 2018).…”

Role of Coherent Structures in Turbulent Premixed Flame Acoustics

“…For instance, vortices in laminar premixed V-flames [10] and turbulent premixed slot jet flames [11] were found to strongly wrinkle the flame front and produce sound. Flame annihilation events such as flame pinch-off and consumption of fresh gas pockets were also shown to be responsible for sound generation in experimental [10,12] and numerical [13][14][15][16] studies of premixed flames. All these previous studies considered the heat release rate fluctuations as the primary source of noise.…”