In many reacting flow problems a thin reactive boundary-layer forms near a surface. Many grid mesh points may be needed to resolve the important chemical species concentration profiles. However, further away from the surface there may be no need for such a finely resolved mesh. A non-uniform grid may be specified by the user, through the "Stretch" parameter, . This parameter can be used to include a mesh that is finer near a surface and more widely spaced as distance from the surface increases.

For cartesian coordinates, if the user has specified mesh points, then the j th grid point will be placed at a distance from the lower wall

(12–33)

where is the channel height. If , a uniform grid is produced. For , the grid is more tightly spaced at the lower boundary. In cylindrical coordinates, the grid will be made finer at the outer boundary through use of an analogous formula.