A New Droplet Breakup Model for DPM Modelling: Applicable for Large Ohnesorge Number, Density-Ratio, and Power-Law Fluids

Secondary droplet breakup models used in discrete phase modeling (DPM) are often limited in their applicability to high-Ohnesorge-number (Oh) fluids, varying density ratios, and non-Newtonian rheology. Classical models, such as TAB and WAVE, rely on simplified deformation or instability assumptions and require extensive empirical tuning outside their validated regimes. In the present work, a generalized droplet breakup framework is proposed by coupling internal flow theory-based deformation dynamics with an energy-based multimodal fragmentation formulation. The model introduces an effective Weber number formulation to account for viscous dissipation, density-ratio effects, and power-law rheology, while regime-dependent stretching dynamics are used to represent vibrational, bag, multimode, and sheet-thinning breakup processes. A trimodal fragmentation representation is incorporated to account for rim, bag, and undeformed-core breakup structures. The model is validated against available experimental and theoretical studies for breakup deformation, rupture time, breakup length, child droplet size, and Sauter mean diameter over a wide range of Oh numbers, density ratios, and power-law indices. The analysis further highlights the limitations of purely IFT-based breakup formulations, showing that physically meaningful deformation prediction alone is insufficient for complete fragmentation modeling without additional closure relations. The proposed framework provides an intermediate approach between purely empirical TAB-family models and instability-based breakup formulations, with improved applicability to high-viscosity and non-Newtonian spray systems.