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

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 et al., J. Fluid Mech. 984, A69 (2024)]. Here, we report a state where jammed clusters emerge in high-density regions of the density waves. The jammed cluster exhibits unique motion, creating downstream high-density regions distinct from the previously reported state of density waves. Additionally, theoretical calculations show that reducing suspension thickness lowers the frequency and global concentration $\mathrm{\Phi }$ threshold for the heterogeneity onset. Notably, the minimal $\mathrm{\Phi }$ 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.