The jet-wedge combinatorial initiation (JWCI) is a novel functional form for initiating an oblique detonation wave (ODW) with reduced total drag within the oblique detonation combustor under the conditions of a low Mach number and low static pressure inflow. It can suppress the instability of the detached ODW. The evolution of the combustion wave during combinatorial initiation is dominated by the intersection between the bow shock wave (BSW) and the oblique shock wave (OSW), and consists of four stages: the shock-induced combustion stage, the shock-deflagration coupling stage, the hybrid combustion stage, and the oblique detonation stage. Three combustion regimes can be formed by using the JWCI: the shock-induced combustion regime, the hybrid combustion regime, and the oblique detonation combustion regime. These regimes have distinct characteristics of combustion and of flow structure that can be controlled by changing two non-dimensional variables: the ratio of momentum flux (J) and the penetration ratio (PR). This is significant as it can facilitate the application of different combustion regimes under a variety of realistic flight conditions. In this study, the criterion for the transformation of the combustion regime is quantitatively investigated, and show that the structure of the combustion wave does not transform until both non-dimensional variables have reached their respective thresholds. J is crucial for determining the combustion regime and facilitating its transformation but the PR accounts only for the height of the combustion wave structure. The work is beneficial for research on the initiation of the ODW in applications of oblique detonation engines.

To gain insight into shock–droplet interaction and detonation wave–droplet interaction in the real physical environment, two solvers named interTwoPhaseLSCentralFoam and interTwoPhaseLSReacCentralFoam are developed under the OpenFOAM® framework. Computations were conducted on the primary breakup of a droplet when subjected to a shock wave and detonation wave. The droplet breakup in shock–droplet interaction divides into two distinct stages when the shock wave is involved. The first stage is a shear-force dominating stage. In the latter stage, there is a high-pressure gradient, which is similar to a discontinuity inside the droplet, leading to the catastrophic breakup. The detonation wave-induced droplet breakup undergoes three stages: initial stage, stretching stage, and balance stage. In the initial stage, the droplet was impacted by the intense compression. Under the impact of the reflected wave on the windward surface, the droplet is continuously stretched, marking the stretching stage. Then, the structure of the parent droplet remains relatively unchanged throughout the detonation, known as the balance stage. During the detonation wave–kerosene droplet interaction, there is a decoupling of detonation wave in certain regions. As kerosene vapor initiates a reaction with the atmosphere and prevails, the detonation wave undergoes a localized re-initiation process behind the incident shock, creating a dual-wave configuration in its entirety. The detonation wave also experienced a shift of mode from hydrogen–air driven to kerosene–air driven.

This investigation examines the atomization flow characteristics and instability mechanisms in a liquid jet in supersonic crossflow (LJISC). Through concurrent deployment of high-speed imaging and phase Doppler particle analysis, we successfully captured two distinct phenomena: the spanwise vortex formation at the atomization zone's lower boundary and the periodic generation and separation of irregular droplet clusters at its apex. Our observations reveal that droplets initially present in the subsonic region were entrained into the supersonic regime by the spanwise vortex, subsequently undergoing fragmentation due to elevated frequency oscillations. To further investigate the gas–liquid interactions in shear-dominated LJISC atomization, we conducted numerical simulations using interTwoPhaseLSELCentralFoam, a compressible two-phase interfacial flow solver developed within the OpenFOAM® framework. We identified a transitional plane demarcating the subsonic-supersonic flow boundary and applied proper orthogonal decomposition (POD) to analyze the temporal evolution of velocity fields across this plane. The POD analysis revealed that shear instability-induced velocity fluctuations in the incoming flow governed the systematic formation and detachment of droplet clusters. Additionally, our findings demonstrate that spanwise-aligned counter-rotating vortex pairs facilitated droplet migration across different velocity strata.

Experimental and three-dimensional simulation studies were performed to investigate the atomization of transverse jet injection under a freestream Mach number of 1.8, using circular, semi-circular, and square injectors. Systematic comparisons of initial spray patterns revealed distinct morphological differences among the three injector geometries. Detailed analysis was performed on the dynamic instability during jet initiation and the subsequent bow shock formation process. Particular attention was given to the recirculation zone developing, with its formation mechanism. Using zonal analysis, the global spray structure and flow field evolution were qualitatively characterized. Results show that higher injection pressure drops significantly increase the bow shock angle and spray penetration depth. Under equal pressure drops, circular injectors generated the largest bow shock angles and penetration depths, whereas semi-circular ones yielded the lowest. At constant mass flow rates, semi-circular injectors resulted in the highest bow shock angles and penetration depths, followed by square and then circular injectors. Analysis of droplet size distribution revealed a characteristic stratification pattern, with larger droplets concentrated at the core and smaller ones dispersed toward the edges. Injector geometry profoundly affected spatial distribution: semi-circular injectors demonstrate a noticeable narrowing effect in spray dispersion, whereas square injectors exhibit localized aggregation phenomena of larger spray particles within their spatial distribution. Droplet size measurements confirmed that square injectors produced larger Sauter mean diameters than the other geometries. Proper orthogonal decomposition analysis identified three dominant fluctuation modes: the first-order mode was governed by low-frequency oscillations, while the second and third modes exhibited streamwise shear-layer instabilities characteristic of Kelvin-Helmholtz vortices.