The computational domain, which is half of a sedimentation tank, is shown in Figure 3. At the two inlet openings, the parallel flow was applied with a uniform horizontal velocity. The turbulence intensity was set at 5%. Inlet flow characteristics under the two scenarios are given in Table 1. Similar to that given in the study by Stamou & Gkesouli (2015), the inlet solids with a density of 2,730 kg/m³ were divided into four classes as given in Table 2 and assumed to be uniformly distributed across the inlet. The sum of the inlet mass flow rates was set as the outlet boundary condition. The bottom of the tank was set as a no-slip smooth wall, and solids were assumed to be deposited and removed from the domain. The direct settling of large particles is expected on the bottom, and other particles are expected to settle and slip along the inclined plates. As noted in the modelling of sedimentation tanks by Gao (2019), the SS removal efficiency is not seriously affected by this no-slip smooth wall assumption to cause a change in the comparisons in the study. The top surface (free surface) of the domain was treated as a free-slip wall, and hence, the normal velocity component and normal gradients of other variables were set to zero. All the vertical walls except the right side of the domain at which symmetry condition was used were treated as hydraulically smooth walls, and no-slip condition was applied. The advection scheme used was upwind. The turbulence model used was the standard k- model.