Large scale effects in weakly turbulent premixed flames

Abstract

In this study we numerically investigate large scale premixed flames in weakly turbulent flow fields. A large scale flame is classified as such based on a reference hydrodynamic lengthscale being larger than a neutral (cutoff) lengthscale for which the hydrodynamic or Darrieus-Landau (DL) instability is balanced by stabilizing diffusive effects. As a result, DL instability can develop for large scale flames and is inhibited otherwise. Direct numerical simulations of both large scale and small scale three-dimensional, weakly turbulent flames are performed at constant Karlovitz and turbulent Reynolds number, using two paradigmatic configurations, namely a statistically planar flame and a slot Bunsen flame. As expected from linear stability analysis, DL instability induces its characteristic cusp-like corrugation only on large scale flames. We therefore observe significant morphological and topological differences as well as DL-enhanced turbulent flame speeds in large scale flames. Furthermore, we investigate issues related to reaction rate modeling in the context of flame surface density closure. Thicker flame brushes are observed for large scale flames resulting in smaller flame surface densities and overall larger wrinkling factors.

Data-driven subfilter modelling of thermo-diffusively unstable hydrogen–air premixed flames

“…Due to their large-scale nature [16], simulations of laminar, intrinsically unstable premixed flames are generally computationally demanding [3]. However, intrinsic instabilities can be effectively investigated in a two-dimensional setting.…”

“…However, intrinsic instabilities can be effectively investigated in a two-dimensional setting. It was shown that large-scale, three-dimensional flames exhibiting hydrodynamic instabilities share most of the morphological features with their two-dimensional counterparts, such as curvature statistics, often used as a marker for such instabilities [16]. These considerations, therefore, justify the choice of a 2D configuration.…”

“…The one-step chemistry dataset has been presented in [2] and it has also been used for modelling purposes in [7]. It has been developed using a well-established numerical framework based on a one-step irreversible reaction controlled by the concentration of a deficient reactant [16][17][18][19]. This framework is implemented in a modified version [20][21][22][23] of the massively-parallel, spectral element [24], incompressible and low-Mach number code nek5000 [25].…”

Experimental and numerical Lattice-Boltzmann investigation of the Darrieus–Landau instability

“…(9) for 2D Bunsen flames [25] and recently some of the authors have measured the dispersion relation in a Hele-Shaw cell [17,21]. Numerically some measurements of growth rates have been performed, first for one-step chemistry [9,10,28] and recently for hydrogen-air flames [11,27,29].…”

Isolating effects of Darrieus–Landau instability on the morphology and propagation of turbulent premixed flames

“…Identifying the instability in a turbulent environment is not as straightforward, because fluctuations of the flame surface resulting from the turbulence are interlaced with disturbances caused by gas expansion, making the distinction difficult even at relatively low intensities. A number of experimental studies (Paul & Bray 1996;Kobayashi, Kawabata & Maruta 1998;Savarianandam & Lawn 2006;Troiani, Creta & Matalon 2015;Bauwens, Bergthorson & Dorofeev 2017) and simulations (Akkerman & Bychkov 2003;Creta, Fogla & Matalon 2011;Creta et al 2016;Fogla et al 2015Fogla et al , 2017Yu, Bai & Bychkov 2015;Lapenna et al 2019) have provided insight on the effect of the DL instability on turbulent flames. More recent studies including DNS for Bunsen flames (Klein, Alwazzan & Chakraborty 2018;Lapenna et al 2019Lapenna et al , 2021Zhang et al 2019;Rasool, Chakraborty & Klein 2021) have shown an interplay between the underlying turbulent field and the flame region under different pressures and Lewis number conditions, highlighting the role that DL instability plays in modifying flame topologies, surface curvature, impact on flame stretch and consumption speed.…”