Sand Particle Sedimentation

Sand Particle Sedimentation CFD Analysis, ANSYS Fluent Training

Introduction

This analysis presents a computational fluid dynamics (CFD) study of sedimentation behavior for three different sand particle sizes using ANSYS Fluent. The study examines how sand particles of varying sizes behave during sedimentation within a fluid medium, offering insight into settling patterns and particle distribution — information valuable for environmental engineering, sediment transport, and water treatment applications.

The geometry was designed in ANSYS Design Modeler as a cylindrical domain, visible through the circular cross-section in the mesh. The domain was optimized to accurately capture particle sedimentation behavior under gravitational influence.

ANSYS Meshing was used to generate a structured hexahedral mesh containing 388,797 elements, providing sufficient resolution to capture flow dynamics, turbulence effects, and particle distribution throughout the domain.

Methodology

A pressure-based, steady-state solver was used to capture the equilibrium state of particle distribution within the fluid. The RNG k-epsilon turbulence model with standard wall functions was selected to represent the turbulent fluid-particle interaction occurring during sedimentation.

The Eulerian multiphase model with implicit formulation was applied to simulate the interaction between the fluid phase and three distinct sand particle sizes — small, medium, and large. Gravitational effects were enabled throughout the simulation to accurately capture the sedimentation process.

Results

Density contours reveal the distribution of the fluid-particle mixture across the domain, ranging from 998.20 kg/m³ to 1114.53 kg/m³, with higher densities concentrated near the bottom — reflecting particle accumulation due to sedimentation.

Static pressure contours range from -80.92 Pa to 200.36 Pa, following a primarily vertical gradient with higher pressures near the domain's base, consistent with hydrostatic pressure distribution and the presence of settled particles.

Volume fraction contours for each particle size reveal distinct settling behavior:

• Large particles (sand-l) reach a maximum volume fraction of 0.32, showing clear stratification and rapid settling concentrated near the bottom of the domain.

• Medium particles (sand-m) show a maximum volume fraction of 0.30, following a similar distribution pattern to the large particles but with a slightly more diffuse upper boundary.

• Small particles (sand-s) also reach a maximum volume fraction of 0.32, but remain far more uniformly distributed throughout the domain, indicating slower settling and greater suspension within the fluid.

The water phase's volume fraction ranges from 0.37 to 1.00, complementing the particle distribution results.

Vertical volume-fraction profiles at the outlet boundary further quantify this size-dependent behavior:

• Large particles show a sharp rise near the bottom, peaking at roughly 0.30.

• Medium particles exhibit a more gradual increase, peaking at approximately 0.28 near the bottom.

• Small particles maintain a much more uniform concentration throughout most of the domain height, peaking at only around 0.035.

These results clearly illustrate size-dependent sedimentation behavior — larger particles settle rapidly and form distinct layers, while smaller particles remain largely suspended throughout the fluid. The findings offer practical insight into particle settling dynamics relevant to sediment transport and particle separation processes across a range of engineering applications.