Flow configuration and pressure effects on turbulent premixed hydrogen jet flames

TL;DR

This study uses direct numerical simulation to analyze how flow configuration and pressure influence turbulent premixed hydrogen jet flames, revealing the critical role of pressure and geometry on flame behavior and small-scale effects.

Contribution

It provides new insights into the effects of flow configuration and pressure on turbulent hydrogen flames, highlighting the importance of small-scale dynamics and curvature effects.

Findings

Pressure increases flame stretch and wrinkling near the nozzle.

Round jets show faster decay of mean local reactivity due to curvature.

Pressure fundamentally alters flame propagation sensitivity to curvature.

Abstract

Turbulent lean premixed hydrogen jet flames are simulated using direct numerical simulation employing detailed chemistry in both slot and round configurations at various pressures. All cases are simulated at a constant jet Reynolds number ($Re_j = 10000$) and a fixed ratio of characteristic length scales. While normalised macroscopic quantities (e.g., flame length, turbulent flame speed) appear comparable across configurations, fundamental discrepancies are observed that originate from the coupling of large- and small-scale effects. Mean local reactivity ($I_0$) decays monotonically downstream, driven by a decreasing Karlovitz number ($Ka^{*}$); however, this decay is modulated by geometry, with round jets exhibiting a faster decline due to mean negative curvature. Pressure is identified as a critical small-scale driver, fundamentally altering flame propagation by increasing the sensitivity of displacement speed to local curvature. At elevated pressures, this sensitivity induces higher flame stretch and accelerates wrinkling near the nozzle, which compounds with geometry-dependent effects, such as the slower decay of mean strain in slot configurations.