Localized jammed clusters persist in shear-thickening suspension subjected to swirling excitation

Abstract

We investigate the dynamic evolution of heterogeneity in shear-thickening suspensions subjected to swirling excitation with a free surface. The uniform state of such a system may lose its stability when the oscillation frequency is above a threshold, and density waves spontaneously form (Shi \textit{et al.} JFM 2024). Here, we report a novel state where jammed clusters emerge in high-density region of the density waves. The jammed cluster exhibits unique motion, creating downstream high-density regions distinct from previously reported state of density waves. Additionally, theoretical calculations show that reducing suspension thickness lowers the frequency and global concentration $\Phi$ threshold for the heterogeneity onset. Notably, the minimal $\Phi$ for instability can be lower than the onset of discontinuous shear thickening transition. We also highlight the role of the free surface in cluster growth and persistence.