A DNS study of extreme and leading points in lean hydrogen-air turbulent flames - part II: Local velocity field and flame topology
Journal article, 2022

Data obtained in recent direct numerical simulations (Lee et al.) of statistically one-dimensional and planar, lean complex-chemistry hydrogen-air flames characterized by three different Karlovitz numbers Ka ranging from 3 to 33 are further analyzed in order to explore local characteristics and structure of (i) extreme points characterized by the peak (over the computational domain) Fuel Consumption Rate (FCR) or Heat Release Rate (HRR) and (ii) leading points that are also characterized by a high FCR or HRR, but advance furthest into unburned reactants. Results show that, on the one hand, common characteristics of flame perturbations (curvature, strain and stretch rates, displacement speed) fluctuate significantly in the extreme or leading, FCR or HRR points and are different in different flames. Moreover, other two-point local quantities such as the local gradients of combustion progress variables or species (e.g., the radical H) mass fractions are different in different flames. Therefore, a common simple configuration of a perturbed laminar flame cannot be used as a catchall model of the entire local structure of zones surrounding the discussed points at various Ka. On the other hand, single-point local characteristics (temperature, species mass fractions, rates of their production) of the FCR extreme points are comparable in all three turbulent flames and in the critically strained planar laminar flame. In particular, the FCRs in the extreme points fluctuate weakly and are approximately equal to each other and to the peak FCR in the critically strained laminar flame. The latter finding implies that (i) the maximum FCR evaluated in the critically strained laminar flame could be used to characterize, in a first approximation, the local FCR in the extreme or leading points in turbulent flames, thus, supporting the leading point concept, and (ii) almost the same extreme FCR can be reached in substantially different local burning structures.

Leading point concept

Turbulent combustion

Hydrogen

Diffusive-thermal effects

Turbulent consumption speed

DNS

Lewis number

Author

Hsu Chew Lee

Southern University of Science and Technology

Peng Dai

Southern University of Science and Technology

Minping Wan

Southern University of Science and Technology

Andrei Lipatnikov

Chalmers, Mechanics and Maritime Sciences (M2), Combustion and Propulsion Systems, Combustions and Sprays

Combustion and Flame

0010-2180 (ISSN)

Vol. 235 111712

Subject Categories

Applied Mechanics

Energy Engineering

Fluid Mechanics and Acoustics

DOI

10.1016/j.combustflame.2021.111712

More information

Latest update

1/19/2022