Effect of Yarn Cross Section on Air Drag for Spandex Yarn

The effect of yarn cross section on the air drag coefficient and the characteristic length is examined for spandex yarn with non-circular cross section.Methods for estimating the air drag of spandex yarns in axisymmetric air flow are investigated. Results obtained are as follows:1) Although the drag coefficient for thin yarns is similar to that of a cylinder, the air drag coefficient of spandex yarn shows similarity to that of a flat plate because of remarkable irregularities in its cross section.2) The drag coefficient for a fixed- end yarn is the same as that for a flat plate. The drag coefficient for a free- end yarn is twice that of the fixed- end yarn. This value is useful in calculating yarn air drag.3) It is efficient and reasonable to use the effective diameter converted from the yarn perimeter length-without any consideration to its irregularity-as the characteristic length of the spandex yarn.