5—AIR-DRAG ON SYNTHETIC-FIBRE TEXTILE MONOFILAMENTS AND YARNS IN AXIAL FLOW AT SPEEDS OF UP TO 100 METRES PER SECOND

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Abstract
Measurements are reported of air-drag on fine textile filaments and yarns in axisymmetric flow in a wind tunnel. The drag coefficient of filaments less than 0.3 mm in diameter can be expressed as a function of the radius Reynolds number, Rea : C D = 0.27 Rea −0.61 for 20 < Rea < 200 and air velocities below 100 m/sec. For Rea < 10, the data fall close to theoretical predictions for axisymmetric laminar flow on cylinders, and they approach the theoretical values for fully developed turbulent flow at Rea > 200. These results imply that 10 < Rea < 200 is a transitional flow regime. Air-drag forces are increased if the filaments are allowed to vibrate in tbe air-stream. It is shown that compact yarns behave as if they were thick filaments of the same surface area and exhibit greatly increased drag forces when they can vibrate freely. Drag forces on textile filaments of diameter 10–100 μm are not affected by the presence of other filaments unless the spacing is less than about 1 mm.