A Priori Direct Numerical Simulation Modeling of Scalar Dissipation Rate Transport in Head-On Quenching of Turbulent Premixed Flames

Abstract

The statistical behavior and modeling of scalar dissipation rate (SDR) transport for head-on quenching of turbulent premixed flames by an inert isothermal wall have been analyzed in the context of Reynolds averaged Navier-Stokes simulations based on three-dimensional simple chemistry direct numerical simulation (DNS) data. It has been found that the density variation, scalar-turbulence interaction, reaction rate gradient, molecular diffusivity gradient, and molecular dissipation terms, i.e., T 2 ; T 3 ; T 4 ; f D ð Þ, and ÀD 2 ð Þ, respectively, act as leading order contributors to the SDRε c transport away from the wall and the turbulent transport and molecular diffusion terms remain negligible in comparison to the other terms. The leading order contributors to the SDR transport have been found to be in a rough equilibrium away from the wall before the quenching is initiated but this equilibrium is not maintained during flame quenching. The predictions of the existing models for the unclosed terms of the SDR transport equation have been assessed with respect to the corresponding quantities extracted from DNS data. No existing models have been found to predict the near-wall behavior of the unclosed terms of the SDR transport equation. The models, which exhibit the most satisfactory performance away from the wall, have been modified to account for near-wall behavior in such a manner that the modified models asymptotically approach the existing model expressions away from the wall. ARTICLE HISTORY

Direct Numerical Simulation of Head-On Quenching of Statistically Planar Turbulent Premixed Methane-Air Flames Using a Detailed Chemical Mechanism

“…Le < 1) flames has been found to be smaller than the corresponding laminar flame value, whereas the quenching distance for turbulent flames with Le = 1, and Le > 1 remains comparable to their corresponding laminar values. This DNS database was utilised to analyse the statistical behaviours of enstrophy [11], FSD [12] and scalar dissipation rate (SDR) [10,13,14] in the near-wall region. Although simple chemistry DNS [2][3][4][5][6][10][11][12][13][14] provided valuable insights into the physical mechanisms pertinent to turbulent premixed FWI, it is yet to be assessed whether correct quantitative behaviours of wall heat flux and flame quenching distance can be obtained from simple chemistry DNS.…”

Multiscale analysis of head-on quenching premixed turbulent flames

“…It can be noticed that the flame behaviour varies with the level of turbulence encountered by the flame. In the case of low turbulence intensity the flame interacts with the wall at a much later time when compared with the higher turbulence intensity cases 28,29,31 . This happens due to greater extent of flame wrinkling in the higher and normalised values of turbulent flame speed (S T /s L ) and a detailed discussion for headon quenching flames can be found in 29,33 (see table 2 in 29,33 ).…”

“…The Direct numerical simulation (DNS) database of Chakraborty and co-authors [28][29][30][31][32] for head-on quenching (HOQ) of statistically planar atmospheric turbulent premixed flames by isothermal inert walls has been considered for this analysis. This database employs a simple 1-step irreversible as well as a skeletal mechanism (details provided below) for chemistry.…”

Flow topology distribution in head-on quenching of turbulent premixed flame: A Direct Numerical Simulation analysis

“…The aforementioned discussion suggests that the flow topology in the region close to the wall is likely to be affected by the presence of the flame and its quenching. To date, considerable effort has been made to analyse flame-wall interaction based on numerical investigations [22][23][24][25][26][27][28][29][30][31][32][33][34][35], but none of these analyses focussed on the flow topology distribution in the near-wall region during unsteady wall-induced flame quenching. This gap in the existing literature is addressed here by analysing the statistical behaviours of the invariants of the velocity gradient tensor ∂ ∂ u x / i j and flow topology distributions at different instants of time as the flame approaches the isothermal wall in the case of head-on quenching of statistically planar turbulent flames with different values of global Lewis number Le (i.e.…”

“…= − Le 0.8 1.2). For this purpose an existing DNS database [30][31][32][33][34][35] of head-on quenching of statistically planar turbulent premixed flames for different values of turbulence intensity and global Lewis number has been considered. All the flow topologies shown in Fig.…”