Faraday wave instability analog in vibrated gas-fluidized granular particles.

Granular materials are critical to many natural and industrial processes, yet the chaotic flow behavior makes granular dynamics difficult to understand, model, and control, causing difficulties for natural disaster mitigation as well as scale-up and optimization of industrial devices. Hydrodynamic instabilities in externally excited grains often resemble those in fluids, but have different underlying mechanisms, and these instabilities provide a pathway to understand geological flow patterns and control granular flows in industry. Granular particles subject to vibration have been shown to exhibit Faraday waves analogous to those in fluids; however, waves can only form at high vibration strengths and in shallow layers. Here, we demonstrate that combined gas flow and vibration induces granular waves without these limitations to enable structured, controllable granular flows at larger scale with lower energy consumption for potential industrial processes. Continuum simulations reveal that drag force under gas flow creates more coordinated particle motions to allow waves in taller layers as seen in liquids, bridging the gap between waves produced in conventional fluids and granular particles subject to vibration alone.