78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V007: Honey, I fluidized the bed

Simultaneous Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities arise in binary granular chute flows when large, dense particles (ρlarge) are stratified above small, light particles (ρsmall). The density difference drives the formation of RT plumes and creates a shear gradient that destabilizes the interlayer interface, enabling the development of KH waves. When ρlarge < ρsmall, no instabilities develop, and particle layers remain segregated. By fluidizing the small particles using upwards gas flow, we observe reduced interparticle friction, a significantly increased the flow velocity, and larger KH wavelengths. We find that fluidization accelerates vertical mixing in configurations where ρlarge > ρsmall, and, notably, permits mixing where ρlarge < ρsmall. When ρlarge = ρsmall, fluidization creates RT plumes that lead to horizontal segregation, which is observed as banding from above the flow.