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  • Micro-jetting and Transvers...
    Ramachandran, Suryanarayan; Yang, Suo

    Combustion and flame, July 2024, 2024-07-00, Letnik: 265
    Journal Article

    We present a highly-resolved 2D numerical simulation of a wedge-induced Oblique Detonation Wave (ODW) using a 9-species 21-reaction chemical kinetic mechanism for a stoichiometric H2-air mixture. Adaptive Mesh Refinement (AMR) is leveraged to obtain a resolution close to the continuum limit at the finest level (Δxfinest=0.78μm=20λ, where λ is the mean-free path of the fuel–air mixture), which spans the ODW front and its transverse waves. The simulation is performed for a sufficiently large domain, enabling us to unveil the multi-zonal structure of the ODW. We capture, for the first time, the onset of microscopic hypersonic jets (micro-jets) far downstream of the wedge tip associated with cellular structures resembling those of a multi-headed Normal Detonation Wave (NDW). In contrast, the upstream “cell-like” structure (christened as “pseudo-cellular” hence) are found to be devoid of these micro-jets with a morphology similar to that of single-headed NDWs, such as spinning/zig-zag detonations in tubes/2D channels, respectively. A detailed investigation into the transverse-shock structure downstream reveals that a colliding pair of transverse waves lead to the micro-jetting phenomenon. The absence of one of the pair of transverse waves in the upstream region results in the observed pseudo-cellular structures. The origin of these transverse waves in an ODW, unclear in previous literature, is shown to arise from coalescing and strengthening of Compression Waves (CWs) that are produced from two distinct mechanisms. During the “early” phase of the ODW stabilization, CWs are formed as a result of local blast events. In the subsequent “middle” phase, these are formed as a result of the shear-layer instabilities coupling with the local shock structure, leading to the so-called left-running transverse waves (LRTWs) upstream and the right-running transverse waves (RRTWs) downstream. The identified mechanisms offer a plausible explanation on why ODWs exhibit a multi-zonal morphology. Novelty and Significance Statement The present study is one of the very few studies in the Oblique Detonation Wave (ODW) literature that includes multi-step chemistry while solving for the compressible reacting Navier-Stokes equations on a large simulation domain revealing the multi-zonal structure of the ODW. Furthermore, the resolution employed for the study approaches the continuum limit, making it on-par with the current state-of-the-art for ODW simulation. For the first time, this study has demonstrated the existence of microscopic hypersonic jets (micro-jets) far downstream of the wedge tip in a wedge-induced ODW and a method to isolate them in numerical simulations, leading to insights on the broader micro-jetting phenomenon in detonations. The existence of a cell-like (which we term as “pseudo-cellular”) region bearing similarity with that of single-headed spinning detonations is also noted due to the absence of a transverse wave family upstream. The exact physical mechanisms leading to the formation of transverse waves in ODW are also investigated, which were previously ambiguous in the literature.