Understanding how dense suspensions transition from viscous to inertial flow regimes is central to predicting their behavior in both industrial and natural systems. In this talk, I will present insights from large-scale Discrete Element Method (DEM) simulations that explore this transition in frictionless, non-Brownian suspensions near the jamming point. At low shear rates, these suspensions exhibit a constant-viscosity, viscous response. However, beyond a critical shear rate, the system enters an inertial regime characterized by shear-rate-dependent viscosity. Our results show that this critical shear rate decreases with increasing volume fraction and vanishes at the jamming threshold—indicating a rheological critical point. I will introduce a scaling framework that collapses data across different volume fractions and highlights the underlying criticality of the transition. Further, I will discuss how this behavior is tied to a diverging microstructural length scale, suggesting a growing spatial correlation in particle dynamics as the system approaches jamming. These findings not only provide a unified view of shear thickening in dense suspensions but also point to broader connections between microscopic structure, rheology, and critical phenomena.
