Front dynamics and surface morphology of wet granular flows down an inclined channel

The flow of wet granular materials released down an inclined channel is investigated experimentally. The observed flow reveals three typical flow regimes corresponding to varying inclination angles, aligning with the dynamics observed in the dry particle case. The presence of interstitial liquid significantly increases the critical angles required for transitions between these regimes. Each regime exhibits distinctive evolving features in front shapes and surface morphologies, primarily depending on grain-scale cohesion induced by capillary forces between particles, which are directly related to particle size. Consequently, a phase diagram encapsulating diverse characteristics of wet granular flows is constructed in the phase space of two relevant parameters, emphasizing the front shape and surface morphology of wet granular flow while concurrently considering the associated flow regime. The generation mechanisms are also discussed based on the effect of cohesion on the motion of particles. Finally, simplified theoretical models, grounded in the law of conservation of momentum and Savage–Hutter theory, are developed to depict the evolving characteristics of the front in different regimes of inclined wet granular flows.