Faraday Waves in Granular Particles Subject to Combined Gas Flow and Vibration*

Experiments show that an analog of the Faraday wave instability forms in granular particles subject to combined vertical vibration and vertical gas flow. As compared to vibration alone, combined gas flow and vibration induces waves at lower vibration strengths and allows waves to persist at higher granular layer heights. Results across different vibration and gas flow conditions for the onset of waves are collapsed by introducing a non-dimensional velocity which incorporates the effects of gas flow and vibration. Continuum numerical simulations using a recently developed granular rheology model are able to reproduce wave patterns in grains subject to vibration with and without gas flow. Simulation results show that the added drag force in cases with gas flow causes more uniform forces and coordination motion among particles throughout the layer, which allow waves to persist at higher layer heights when gas flow is used.