In this paper, the coupled level set volume of fluid and the large eddy simulation methods are adopted to perform three-dimensional simulations of the shear breakup of a water droplet. We investigate the effect of airflow pressure (1–3 atm) on the temporary deformation and breakup characteristics, including the breakup initiations, the cross-stream, and streamwise deformations. In addition, special attention is paid to subsequent sub-droplet size distributions, which are generally ignored by many researchers. The results indicate that different morphologies on the surface of the droplets in the shear breakup regime are in relatively good agreement with the available experimental visualizations. Based on the present method, the physical mechanism for the variations in the wake recirculation with the development of Rayleigh–Taylor instability waves is discussed. Furthermore, higher airflow pressures can significantly increase cross-stream and streamwise deformations. However, the corresponding breakup initiations at high airflow pressures are much earlier than those of parent droplets at low airflow pressures. Specifically, a reduction of 12.17% in the mean sub-droplet sizes is obtained as the airflow pressure increases from 1 atm to 2 atm, while a reduction of less than 0.1% in the mean sub-droplet sizes is obtained at higher airflow pressures from 2 atm to 3 atm. Eventually, there are linear growths of the aggregate superficial area ratios (0.996–28.2) and the mass ratios (3.55%–64.29%) of the sub-droplets to the parent droplet.

This paper adopts the coupled level-set and volume-of-fluid (CLSVOF) and the large eddy simulation (LES) methods to simulate the deformation and breakup of an n-Decane droplet under the action of shock wave. We aim to investigate the effects of the shock Mach number and droplet diameter on temporary deformation and breakup characteristics at high Weber numbers from 5813 to 22380. Additionally, special attention is paid to subsequent sub-droplet size distributions, which many researchers generally ignore. The results indicate that the evolution of droplet deformation and breakup in the shear breakup regime generally agrees with the obtained experimental data. Based on the present methods, the physical mechanisms for variations of multiple recirculation zones and the development of Kelvin-Helmholtz instability in wave formation are discussed. Larger shock Mach number and smaller droplet diameter can significantly increase the cross-stream and stream-wise deformations. Moreover, both relaxation and breakup times are directly proportional to the initial droplet diameters but inversely proportional to the shock Mach numbers. Eventually, as the shock Mach number increases, the superficial area and mass ratios of sub-droplets to parent droplets all increase from 5.596 to 8.278 and from 23.38% to 38.38%, while the ratios respectively increase from 2.652 to 18.523 and from 4.63% to 92.7% as the droplet diameter decreases.

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In this work, to promote deflagration to detonation transition (DDT), a designed hot jet in a pre-detonator is produced to initiate the detonations in the main detonation tube. We perform two-dimensional simulations of the DDT process for low-volatile fuel (n-decane) mixed with nitrogen and oxygen based on the Eulerian−Lagrangian approach. The effects of fuel atomization, vaporization, and shock focusing on the flame acceleration and DDT are discussed under different nitrogen dilution ratio and droplet size conditions. The results show that the flame acceleration process can be divided into slow and fast deflagration stages. Additionally, initiation times are mainly determined by the fuel atomization and evaporation in the slow deflagration stage, which dominates the entire DDT time. Furthermore, there are different intensities of hot jets rather than stable detonation waves formed at the pre-detonator exit. Moreover, local decoupling and re-initiation events are detected near the internal wall of the U-bend, inducing the overdriven detonation decaying into stable detonation waves in the smooth tube. Results also demonstrate that the detonation pressure and velocity decrease by 13.56% and 12.55% as the nitrogen dilution ratio increases from 0.5 to 2. In particular, as the nitrogen dilution ratio continued to increase to 2.25, the development in DDT is similar, but the jet intensity is significantly weakened. While as the droplet size increases from 10 to 40 um, the detonation pressure and velocity decrease only by 2.69% and 1.49%, respectively.