Vertical stratification and local flow states of dense particle-liquid inclined open channel flow based on internal observation

This study experimentally investigated the dense particle-liquid open channel flows over smooth and rough inclined beds using the refractive index matching (RIM) technique. The internal flow profiles of the granular phase, including velocity, shear rate, granular temperature, and solid concentration, were reconstructed through image processing techniques. The vertical stratification behavior of dense particle-liquid channel flows under various inclination angles and inflow heights was examined. Results indicated that four fundamental local flow states exist in dense particle-liquid channel flows: plug flow, ordered friction flow, disordered friction flow, and collision flow. These flow states can be combined to construct the stratification flow in the granular phase of two-phase dense granular flows. There are three flowing superimposed modes on the smooth bed: plug flow, disordered friction flow + plug flow, and disordered friction flow. We identified three typical superimposed flow modes on the rough bed: ordered friction flow + disordered friction flow (OF-DF flow), collision flow + disordered friction flow (C-DF flow), and collision flow + disordered friction flow + plug flow (C-DF-P flow). The complex flow structure observed under various operating conditions is simplified through the superposition of the fundamental local flow states. This study significantly advances the understanding of the intricate internal flow behavior and structure of dense particle-liquid two-phase flows.