Anchoring of Turbulent Premixed Hydrogen/Air Flames at Externally Heated Walls

TL;DR

This study combines experimental and numerical methods to investigate how turbulent hydrogen/air flames anchor to heated walls, emphasizing heat transfer effects, turbulence modeling, and diffusion processes for improved understanding.

Contribution

It introduces a comprehensive analysis of wall-anchored turbulent hydrogen/air flames using advanced numerical models validated by optical measurements, highlighting the importance of diffusion and heat transfer treatments.

Findings

Wall heat transfer influences ignition and quenching.

Eddy Dissipation Concept significantly affects flame shape.

Full multicomponent diffusion improves simulation accuracy.

Abstract

A joint experimental and numerical investigation of turbulent flame front anchoring at externally heated walls is presented. The phenomenon is examined for lean hydrogen/air mixtures in a novel burner design, which comprises a cylindrical burning chamber converging into a glass pipe as well as a wall heating assembly at their intersection. The transparent part allows for optical OH* chemiluminescence measurements serving as a basis for numerical validation. For a comprehensive numerical evaluation the effect of heat loss on different hydrogen/air chemical reaction mechanisms is reviewed in a preparatory one-dimensional flame study. The subsequent numerical investigation focuses on the application of the Eddy Dissipation Concept (EDC) as a turbulence-chemistry interaction model in the realm of wall anchoring turbulent flames. All simulations are based on the Reynolds time-averaged formulation of the Navier-Stokes equations and feature axisymmetric domains. The influence of different two-equation turbulence models and EDC modeling constants are discussed. Since wall heat transfer is responsible for ignition as well as quenching of the flame front, a special focus is put on boundary layer resolving near-wall treatment. A qualitative comparison between simulations and experiment is performed for multiple operating conditions. These are selected to display the influence of equivalence ratio, bulk Reynolds number and unburnt mixture temperature. While the choice of RANS-based turbulence model has a distinguishable impact, EDC modeling coefficients exhibit a more significant influence on flame shape and length. It is only surpassed by the impact of correct diffusion treatment on reacting lean hydrogen/air mixtures. To depict this behavior as accurately as possible, full multicomponent diffusion treatment using the Maxwell-Stefan equation is applied.