Title: Evaporation of Finite-Size Ammonia and n-Heptane Droplets in Weakly Compressible Turbulence: An Interface-Resolved DNS Study Show Chinese title

Title: 有限尺寸氨水和正庚烷液滴在弱可压缩湍流中的蒸发：界面解析直接数值模拟研究

Abstract: This study presents direct numerical simulation (DNS) of finite-size, interface-resolved ammonia and n-heptane droplets evaporating in decaying homogeneous isotropic turbulence. Simulations are conducted for each fuel to model the dynamics in a dense spray region, where the liquid volume fraction exceeds $\mathcal{O}(10^{-2})$. The focus is on investigating the complex interactions between droplets, turbulence, and phase change, with emphasis on droplet-droplet interactions and their influence on the evaporation process. The present study also explores how varying turbulence intensities affect the evaporation rates of each fuel, unveiling the differences in the coalescence and energy transfer from the liquid to the gaseous phase. The results reveal that, when comparing ammonia with n-heptane with equal liquid volume fractions, ammonia exhibits faster initial evaporation due to its higher volatility. However, this rate declines over time as frequent droplet coalescence reduces the total surface area available for evaporation. When numerical experiments are initialized with equal energy content, increasing turbulence intensity enhances the evaporation of n-heptane throughout the simulation, while ammonia evaporation soon becomes less sensitive to turbulence due to rapid vapor saturation. These findings are relevant to improving predictive CFD models and optimizing fuel injection in spray-combustion applications, especially under high-pressure conditions. Show Chinese abstract

Abstract: 本研究展示了有限尺寸、界面解析的氨水和正庚烷液滴在衰减的均匀各向同性湍流中蒸发的直接数值模拟（DNS）。 针对每种燃料进行模拟，以建模密集喷雾区域中的动力学特性，其中液体体积分数超过$\mathcal{O}(10^{-2})$。 重点在于研究液滴、湍流与相变之间的复杂相互作用，尤其关注液滴间的相互作用及其对蒸发过程的影响。 本研究还探讨了湍流强度的变化如何影响每种燃料的蒸发速率，揭示了液滴聚结以及从液相到气相的能量传递差异。 结果显示，当比较具有相同液体体积分数的氨水和正庚烷时，由于其更高的挥发性，氨水表现出更快的初始蒸发。 然而，随着时间推移，这一速率下降，因为频繁的液滴聚结减少了可用于蒸发的总表面积。 当数值实验以相等的能量含量初始化时，增加湍流强度在整个模拟过程中增强了正庚烷的蒸发，而氨水的蒸发很快变得对湍流不那么敏感，因为快速达到蒸汽饱和。 这些发现对于改进预测性的计算流体力学（CFD）模型和优化喷雾燃烧应用中的燃油喷射具有重要意义，尤其是在高压条件下。