Fiber–Obstacle Interaction in a Shear Flow

Fiber–obstacle interactions are important in refining processes, where fibers interact with solid surfaces under shearing flow. In this study, a coupled CFD–DEM approach is used to investigate the effects of obstacle height, fiber flexibility, fiber length, and flow velocity on the flow field, fiber motion, and shear stress around an obstacle. The fluid flow is solved using OpenFOAM and fiber motion using LIGGGHTS, with fibers represented by bonded spherical particles. Three obstacle heights, h/H = 0.25, 0.50, and 0.75, are considered in a 1 mm high channel. Increasing the obstacle height promotes fiber accumulation and modifies the flow structure around the obstacle. The effect of fibers on obstacle shear stress depends strongly on obstacle height: compared with the fiber-free case, the averaged shear stress increases by approximately 68% for h/H = 0.25, changes by only 3% for h/H = 0.50, and decreases by approximately 31% for h/H = 0.75. The reduction at the highest obstacle may be attributed to the formation of a fiber layer that partially shields the obstacle from the main flow. Fiber flexibility and length further influence the balance between fiber–wall interaction, fiber–fiber interaction, and flow-induced forces. These results demonstrate that obstacle geometry and fiber properties jointly control momentum transfer and fiber accumulation around obstacles.