A flame particle tracking analysis of turbulence–chemistry interaction in hydrogen–air premixed flames

Abstract

Interactions of turbulence, molecular and energy transport coupled with chemistry play a crucial role in the evolution of flame surface geometry, propagation, annihilation and local extinction/re-ignition characteristics of intensely turbulent premixed flames. This study seeks to understand how these interactions affect flame surface annihilation of lean hydrogen-air premixed turbulent flames. Direct numerical simulations (DNS) are conducted with detailed reaction mechanism and transport properties for hydrogen-air flames, at different parametric conditions. Flame particle tracking (FPT) technique is used to follow specific flame surface segments. An analytical expression for the local displacement flame speed (S d ) of a temperature isosurface is considered and the contributions of transport, chemistry and kinematics on the displacement flame speed at different turbulence-flame interaction conditions are identified. In general, the displacement flame speed for the flame particles is found to increase with time for all conditions considered. This is because, eventually all flame surfaces and their resident flame particles approach annihilation by reactant island formation at the end of stretching and folding processes induced by turbulence. Principal curvature evolution statistics obtained using FPT suggest that these islands are ellipsoidal on average, enclosing fresh reactants. Further examinations show that the increase in S d is caused by the increased negative curvature of the flame surface and eventual homogenization of temperature gradients, as these reactant islands shrink due to flame propagation and turbulent mixing. Finally, the evolution of the normalized, averaged, displacement flame speed vs. stretch Karlovitz number was found to collapse on a narrow band, suggesting that a unified description of flame speed dependence on stretch rate may be possible in the Lagrangian description.

Direct Numerical Simulations of Hotspot-induced Ignition in Homogeneous Hydrogen-air Pre-mixtures and Ignition Spot Tracking

“…In previous studies tracking a premixed flame (e.g., [26]), the position of a flame particle vs. time is typically described by, where x p ( t ) is the flame particle position, u ( x p ( t ), t ) is the flow velocity at position x p ( t ), S d ( x p ( t ), t ) is the local displacement speed of the flame isosurface with n being the unit vector normal to the flame front.…”

Modelling of the turbulent burning velocity based on Lagrangian statistics of propagating surfaces

“…Chaudhuri (2015) developed a method of Lagrangian flame particles to study the time-history of specific portions and associated properties of the flame surface. This method has been utilized to analyze turbulencechemistry interactions (Chaudhuri 2015) and extinction dynamics in H 2 /air premixed flames (Uranakara et al 2016). Dave et al (2018) developed a backward flame-particle tracking method to locate the origin of the complex topology and physico-chemical state in a fully developed turbulent premixed flame.…”

A DNS Study of Sensitivity of Scaling Exponents for Premixed Turbulent Consumption Velocity to Transient Effects

“…[36][37][38][39] or shown in recent papers [40,41]. Accordingly, from purely numerical perspective, the present simulations are inferior to modern DNS studies that allow for both thermal expansion and complex chemistry in intense (u /S L 1) turbulence, e.g., [41][42][43][44][45][46][47]. However, the invoked assumptions are fully adequate to the qualitative goal of the present work.…”