Ignition, flame structure and near-wall burning in transverse hydrogen jets in supersonic crossflow

Abstract

We have investigated the properties of transverse sonic hydrogen jets in hightemperature supersonic crossflow at jet-to-crossflow momentum flux ratios J between 0.3 and 5.0. The crossflow was held fixed at a Mach number of 2.4, 1400 K and 40 kPa. Schlieren and OH * chemiluminescence imaging were used to investigate the global flame structure, penetration and ignition points; OH planar laser-induced fluorescence imaging over several planes was used to investigate the instantaneous reaction zone. It is found that J indirectly controls many of the combustion processes. Two regimes for low (<1) and high (>3) J are identified. At low J, the flame is lifted and stabilizes in the wake close to the wall possibly by autoignition after some partial premixing occurs; most of the heat release occurs at the wall in regions where OH occurs over broad regions. At high J, the flame is anchored at the upstream recirculation region and remains attached to the wall within the boundary layer where OH remains distributed over broad regions; a strong reacting shear layer exists where the flame is organized in thin layers. Stabilization occurs in the upstream recirculation region that forms as a consequence of the strong interaction between the bow shock, the jet and the boundary layer. In general, this interaction -which indirectly depends on J because it controls the jet penetration -dominates the fluid dynamic processes and thus stabilization. As a result, the flow field may be characterized by a flame structure characteristic of multiple interacting combustion regimes, from (non-premixed) flamelets to (partially premixed) distributed reaction zones, thus requiring a description based on a multi-regime combustion formulation.

Wall-Modeled Large-Eddy Simulation of Autoignition-Dominated Supersonic Combustion

“…This is supported by direct numerical simulation results by Aspden et al [4] and subsequently experimentally confirmed by Zhou et al [5]. This combustion regime occurs in the near-wall burning of a fuel jet in a supersonic crossflow: for example, as in [6] and as will be demonstrated with a posteriori analysis of the current simulations. Thus, the goal of the current work is to develop a combustion modeling approach for the LES of high-speed combustion flows that can capture both ignitiondelay and DRZ combustion effects.…”

“…Here, we use the McBride and Gordon thermodynamic curve fits [31] for the thermodynamics computations. Figure 1 plots ζ and the water (H 2 O) mass fraction as a function of ρ; Z; τ at fixed e for the EVM table constructed to represent the hydrogen-air experiments of Gamba and Mungal [6]. The detailed chemical kinetics model of Burke et al [28] was used to construct the table.…”

“…The EVM approach was used to simulate the normal injection of hydrogen in supersonic crossflow experiments of Gamba and Mungal [6] at two jet momentum flux J conditions. See the work of Saghafian et al [18] for corresponding compressible flameletprogress variable simulations.…”

“…The flow conditions are taken from the work of Gamba and Mungal [6] as T ∞ 1400 K, p ∞ 40 kPa, and u ∞ 1800 m∕s. This corresponds to a freestream density of 0.0995 kg∕m 3 , a Mach number of 2.48, and a Reynolds number of 6550 based on the 2 mm jet diameter and freestream conditions.…”

“…The focus is on the development of a numerical method that is rigorously consistent with the thermochemical model so that the numerical method correctly reflects the variations in the thermodynamic state. We apply the proposed numerical flux function to the supersonic reacting hydrogen injection experiments of Gamba and Mungal [6] using the hydrogen-air chemical kinetics model of Burke et al [28].…”