Interface evolution and secondary breakup of a single n -decane droplet exposed to airflow: A CLSVOF–LES study

Secondary breakup of fuel droplets in airflow governs spray atomization and fuel–air mixing, yet the mechanisms underlying interfacial instability and fragment formation under varying conditions remain insufficiently understood. Two-dimensional simulations examine the interface evolution and secondary breakup of individual n-decane droplets with initial diameters of 1 and 2 mm. A coupled level-set and volume-of-fluid method, combined with large eddy simulation and adaptive mesh refinement, resolves droplet deformation, interface evolution, and breakup. The results show that the droplets undergo shear breakup governed by the coupled effects of the windward–leeward pressure difference, wake recirculation, and interfacial shear. During the early stage, the pressure difference between the windward stagnation region and the leeward low-pressure wake drives global deformation. As deformation progresses, wake separation and vortex–shear interactions amplify interfacial disturbances, promoting lateral spreading, liquid-film stretching and thinning, ligament formation, surface stripping, and sub-droplet detachment. Increasing airflow pressure accelerates deformation and shortens the breakup time, while smaller droplets respond more rapidly to aerodynamic forcing because of their lower inertia. The sub-droplet count histograms exhibit an approximately log-normal-like tendency, with the modal size interval shifting toward smaller values as airflow pressure increases and the initial droplet diameter decreases. These findings clarify the coupled effects of airflow pressure and initial droplet size on shear breakup and provide insight into fuel-spray atomization.