Effect of transient shell formation on Shock-induced atomization of an evaporating nanofluid droplet

Abstract: This study investigates the shock-induced atomisation dynamics of an acoustically levitated TM-10 nanofluid droplet subjected to a coaxially propagating blast wave and subsequent compressible vortex ring, generated using a compact wire-explosion shock source. The blast wave imposes a sharp velocity discontinuity, followed by a decaying flow field and a vortex-dominated interaction that drives droplet disintegration. Laser-induced heating promotes evaporation, increasing nanoparticle concentration, viscosity, and agglomeration within the droplet. Progressive evaporation leads to interfacial nanoparticle accumulation, initiating a sol-gel transition when the local volume fraction exceeds the gelation threshold, and ultimately forming a solid outer shell as the maximum packing limit is approached. Shock interactions are systematically examined across three evaporation stages: (i) steady liquid phase, (ii) gel-shell phase, and (iii) solid-shell phase. Each regime exhibits distinct atomisation responses due to the evolving interfacial morphology. In the gel-shell regime, deformation is resisted by the viscous shell, producing a bag-on-sheet mode, followed by puncture, jetting, and eventual shell delamination. In the solid-shell regime, interactions intensify, resulting in brittle fragmentation and catastrophic fracture. The findings reveal how evaporation-driven interfacial transitions fundamentally alter breakup mechanisms under transient shock loading. By linking nanoparticle transport, shell formation, and flow droplet interaction across multiple timescales, this work establishes new physical insights into the atomisation of complex, multicomponent, multiphase, and transiently evolving droplets under extreme aerodynamic conditions