The word “screen” refers to a barrier with distributed perforations such as a wire gauze, grille, or perforated plate. The screen is assumed to have a width, which is small compared to the resolved length-scales of the flow field and can thus be modeled as an edge (in 2D) or surface (in 3D). This idea permits an economic implementation of the screen, where the details of the barrier need not be resolved. The general influence of a screen on the flow field is a loss in the normal momentum component, a change in direction (related to a suppression of the tangential velocity component), attenuation of the turbulence kinetic energy and preservation of the turbulence length scale (Ref. 16). The conditions across the screen are expressed as,

− and + refer to the upstream and downstream side of the screen, whereas K and η are the screen resistance and refraction coefficients. Isotropic turbulence is expected on the downstream side of the screen, hence,

The attenuation of the turbulence kinetic energy (Equation 3-47) is based on the suppression of the tangential velocity (Equation 3-46) and the changes in ε and ω are determined by the assumption of preservation of the turbulence length-scale across the screen.

The Screen feature provides three commonly used correlations for K (Ref. 17). The following correlation is valid for wire gauzes

Here σs is the solidity (ratio of blocked area to total area of the screen) and d is the diameter of the wires. For a square mesh, the following correlation is applied,

The following correlation for wire gauzes (Ref. 18) gives reasonable values for η for a wide range of applications and has been included in the implementation,