Flow configuration and pressure effects on turbulent premixed hydrogen jet flames

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.

Figures (9)

• Figure 1: Isosurfaces of each case at $c_{F} = 0.9$, coloured by heat release rate. Top row: slot cases, bottom row: round cases, left column: 1atm, middle column: 5atm, right column: 10atm. Each case normalised in size by $H$ or $d_{j}$.
• Figure 2: Fuel flux as a function of streamwise distance for all cases. Slot cases are denoted with solid lines, round cases with dotted lines. Pressures of 1, 5 and 10atm are shown with black, red and blue lines, respectively.
• Figure 3: Normalised turbulent burning velocity $s_{T}/s_{L}$ (top), mean local reactivity $I_{0}$ (middle) and flame wrinkling $\Psi$ (bottom) as a function of streamwise distance.
• Figure 4: Karlovitz number $Ka^{*}$ as a function of the normalised streamwise distance. All cases exhibit a $\sim x^{0.5}$ decay, shown by the magenta line.
• Figure 5: Turbulent enhancement of $I_{0}$ ($I_{0}/I_{0}^{*} -1$) plotted as a function of $Ka^{*}$. Note that the inlet is positioned on the right, and the flame tip on the left.