Sinking the bed: How geometry and fluid forces affect particle suspension

Many environmental flow processes, including river and coastal sediment transport, snow transport, and erosion processes, involve multiple particles comprising a particulate bed. How those particles interact with fluid flows, deposit onto the bed, and resuspend in the fluid can dictate the evolution of these environments.

Mohammad Jabarifar and Jeffrey Marshall used computational modeling to examine the hydrodynamic forces acting on exposed particles at the surface of a particulate bed, focusing on the interactions between multiple particles and the effects of bed porosity.

“Although previous studies have examined forces on particles near walls or above simple beds, the combined influence of realistic porous bed structures and interactions between multiple exposed particles has remained poorly understood,” said Marshall. “We wanted to better understand how local bed geometry and neighboring particles collectively influence the hydrodynamic forces and torques responsible for particle motion.”

The duo used a particle-resolved lattice Boltzmann method to analyze the flow around multiple exposed particles and directly compute the hydrodynamic forces and torques. They found that a larger gap distance between bed particles caused exposed particles to sink deeper into the particulate bed, decreasing drag and lift forces significantly. However, this effect diminishes with the number of particles present, and for large numbers of exposed particles the gap distance has nearly no effect on fluid forces.

The authors are planning to expand their work by examining the effects of flow on particulate beds over time.

“In many natural systems, the flow varies with time rather than remaining steady, which can significantly influence particle resuspension,” said Marshall. “We are particularly interested in examining how time-dependent flow interacts with local bed structure, particle exposure, and shielding effects to influence incipient particle motion.”

Source: “Coupled effects of bed structure and neighboring particles on forces, torques, and incipient motion of exposed particles above a particulate bed,” by Mohammad Jabarifar and Jeffrey S. Marshall, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0326422 .