Instability growth and internal void dynamics in shear-thinning jet atomization: A direct numerical simulation study

Gel-based propellants have gained significant attention in aerospace and propulsion applications, yet the atomization characteristics of gel-based propellants with shear-thinning behavior are still lacking understanding. In this study, the primary atomization behavior of shear-thinning fluid jets is investigated using a three-dimensional coupled Volume of Fluid and Lagrangian Particle Tracking model integrated with direct numerical simulation. A modified power-law model is employed to accurately capture the shear-dependent viscosity, and the numerical approach is rigorously validated. The results show that shear-thinning jets exhibit earlier onset and faster radial growth of surface instabilities compared with Newtonian jets. During the early stage, a viscosity–pressure positive-feedback mechanism accelerates wave amplification, while downstream axial curvature effects dominate and suppress further growth, consistent with the observed reduction in cumulative deviation beyond ≈11D. Interface steepening enhances aerodynamic shear and induces multilayer recirculation near surface waves, promoting the formation of internal voids within the liquid column. With increasing consistency index k and decreasing power-law index n, the maximum cumulative deviation rises from 2.77D to 4.14D, while the length of the positive-feedback region decreases from 11.0D to 9.46D, indicating that stronger shear-thinning effects accelerate the amplification of instability waves while confining their axial growth. These findings provide new insights into the nonlinear instability dynamics and interfacial evolution during the breakup of shear-thinning jets and establish a theoretical foundation for optimizing fuel injection systems utilizing rheologically complex or gel-based propellants.