“…An opposite trend was obtained by Schwartz and Tejada (1972). According to Roper III et al (1999) the surface roughness seems to have no appreciable impact on air entrainment velocity, although from an aerodynamic point of view, surface roughness induces earlier laminar-turbulent transition (Ardekani et al, 1997). Web permeability may play an important role when the pressure gradient in the web is high enough to allow air di usion through the porous web.…”