Abstract
When a pure jet or a force plume is discharged into semi-infinite quiescent environments, it increases its width and cross-sectional volumetric flux by involving the ambient fluids. In order to correctly calculate the so-called entrainment phenomena with CFD, open boundaries are needed to allow fluids pass through the boundary. This paper firstly compared the advantages and disadvantages of several mostly used boundary conditions, with a laminar planar jet discharged into stagnant fluids. A simplified traction-free boundary condition is then proposed for the lateral open boundaries. The new boundary condition makes the entrainment possible with a higher numerical stability. It is easy to implement, was introduced to laminar planar and round jet, then was validated with turbulent planar and round jet under standard and realizable k-ε models.
