circular perforation; triangular 60°

square perforation; staggered 45°

          open area s = 0,906 (d/a)²

open area s = 0,906 (d/a)²

          circular perforation; straight 90°

rectangular perforation, straight

          open area s = 0,785 (d/a)²

open area s = (c1*c2) / (a1*a2)

          circular perforation; staggered 45°

rectangular perforation; staggered

          open area s = 0,785 (d/a)²

open area s = 2 * (c1*c2) / (a1*a2)

          square perforation; straight 90°

slotted perforation; straight

          open area s = (c/a)²

open area s = ((c1*c2) – 0,215*c1²) / (a1*a2)

          square perforation; staggered

slotted perforation; staggered

          open area s = (c/a)²

open area s = 2 * ((c1*c2) – 0,215*c1²) / (a1*a2)