Simulation of Flow in Rectangular Clarifiers

A numerical model has been developed to simulate flow in rectangular clarifiers operating at neutral density conditions. The equations of motion in the $\psi -\omega$ format are solved using a finite‐difference method. A two‐step ADI three time level, weighted upwind‐centered difference scheme is used to solve the ω‐equation. The centered‐difference analog of the ψ‐equation is solved using the SOR method. A truncation convergence criterion was derived where the local Courant Number has to be kept below one. Computational stability depends on both Courant number and grid Reynolds number. A variable size mesh reduces both execution time and storage requirements without loss of solution accuracy. A partial slip boundary condition improves on the turbulence model. The finite difference and experimental flow fields are in good agreement.