Flow regimes and impact loading characteristics of dense particle–liquid flows interacting with a cylindrical obstacle

The interaction between dense particle-liquid flows and obstacles plays a central role in debris-flow impact processes and the performance of protective structures, yet the associated flow regimes and impact loading characteristics remain insufficiently resolved by laboratory experiments. In this study, inclined dense particle-liquid flow impacts on a cylindrical obstacle are investigated using a laboratory-scale experimental system that combines synchronized multi-view high-speed imaging with direct force measurements. The experimental setup enables simultaneous observation of flow kinematics, particle-fluid distribution patterns, and load time histories during flow–structure interaction. Experiments are conducted over a range of slope angles and solid volume fractions representative of dense debris-flow conditions. The multi-view imaging configuration allows identification of three-dimensional flow features, including upstream shock formation, particle circulation zones, flow expansion, and localized particle-depleted regions near the obstacle.

Results indicate that the interaction process exhibits distinct flow regimes primarily controlled by solid volume fraction and the spatial structure of the upstream shock. At higher solid volume fractions (φ = 55%), the incoming flow develops a compact, high-shear shock front characterized by intense particle collisions and rapid momentum dissipation. This flow configuration promotes the formation of a stable upstream accumulation, accompanied by pronounced particle clustering and particle-liquid separation, and supports a clear transition from short-duration dynamic impact to a sustained reflection wave regime. In contrast, at lower solid volume fractions (φ = 45%), the shock structure is more diffuse and is frequently disrupted by persistent vertical jets and fragmented particle impacts. In this case, particle–liquid separation is weak or short-lived, and the loading remains strongly non-stationary without the establishment of a stable reflection structure.

These experimental observations provide new insights into flow-regime-dependent impact loading mechanisms of dense particle-liquid flows and offer a physical basis for improving debris-flow impact modelling and the design of protective structures.