In this paper a method is developed to define multiple open boundary (OB) conditions in a simplified vortex settling basin (VSB). In this method, the normal component of the momentum equation is solved at the OBs, and tangential components of vorticity are calculated by solving vorticity transport equations only at the OBs. Then the tangential vorticity components are used to construct Neumann boundary conditions for tangential velocity components. Pressure is set to its ambient value, and the divergence-free conditionis satisfied at these boundaries by employing the divergence as the Neumann condition for the normal-direction momentum equation. The 3-D incompressible Navier–Stokes equations in a primitive-variable form are solved using the SIMPLE algorithm. Grid-function convergence tests are utilized to verify the numerical results. The complicated laminar flow structure in the VSB is investigated, and preliminary assessment of two popular turbulence models, k-epsilon and k-omega, is conducted.

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