ABSTRACT The aerodynamic properties of 15 knitted fabrics of varying cover factor, yarn, and fibe... more ABSTRACT The aerodynamic properties of 15 knitted fabrics of varying cover factor, yarn, and fiber compositions were investigated for their aerodynamic properties on circular cylinders in a wind tunnel. Measurements of the drag force, pressure distribution, and the Particle Image Velocimetry (PIV) technique were used in order to obtain a better understanding of the effects of yarn, fiber composition, cover factor, and elastic deformation on the flow field and drag coefficient. It was clearly demonstrated from the drag force measurements that the yarn construction and fiber composition have a substantial effect on the drag coefficient (CD), with fabrics composed of spun yarn experiencing no CD-drop as opposed to those composed of filament yarn, and being almost unaffected by the cover factor in the range of Reynolds numbers investigated. Hairiness of the spun yarn was found to minimise the drag-reducing effect of the boundary layer transition and increase the trans-critical drag. The hairy surface layer also appeared to retard the turbulent boundary layer as almost no pressure recovery was observed prior to separation on the cylinder model. The effect of elastic deformation was investigated by image analysis of scanned textile samples, and demonstrated that surface roughness might not be directly correlated to cover factor when the fabrics are stretched. Different elastic behavior of fabrics with different cover factors was also found to affect the structure of the knit surface and thus their aerodynamic behaviour. The onset of drag crisis found in drag measurements confirmed the deviation from a sequence determined solely by cover factor.
The aerodynamic drag force acting on a circular cylinder clad with knitted wool and polyester tex... more The aerodynamic drag force acting on a circular cylinder clad with knitted wool and polyester textiles has been investigated in wind tunnel experiments in this study. Particle image velocimetry (PIV) was utilized to determine the flow field, both around the separation point and a wake profile in the close wake. The drag forces and the characteristic C D curves were determined over a range of Reynolds numbers expected to contain flow transition, for a number of knitted textiles having different surface roughness characteristics. The effects of knitting parameters and type of yarn on the flow field were investigated. The parameters of interest to be examined were critical Reynolds number, separation point, growth of the wake and wake profile. The wool and polyester textiles examined showed dissimilar effects on the flow field. Both were clearly adding surface roughness, and hence tripping transition to turbulence at a lower Reynolds number than for the smooth cylinder. The wool textile did however turn out be a more effective turbulence trigger than expected.
The paper addresses the effects of geometry and physical parameters of knitted fabric structures ... more The paper addresses the effects of geometry and physical parameters of knitted fabric structures on their aerodynamic and comfort properties. In order to evaluate whether significant aerodynamic and comfort advantages may be achieved by changing the ...
Wind tunnel testing has been carried out on nine-knitted single jersey fabrics (100% polyester) u... more Wind tunnel testing has been carried out on nine-knitted single jersey fabrics (100% polyester) using cylinder and leg models to determine its aerodynamic behaviour over a range of speeds (20-80 km/h) representative of sports activities. Strong correlation between fabric manufacturing (cover factor) and fabric roughness and aerodynamic parameters has been established. Similar aerodynamic behaviour of fabrics was observed when tested on the cylinder model and on the leg model.
In this paper, the double layer concept of knitted fabrics suitable for performance sportswear, w... more In this paper, the double layer concept of knitted fabrics suitable for performance sportswear, where each layer is separate from the other, was studied. Aerodynamic properties of this assembly, where the base layer is made of 100% wool and an external layer made of 100% filament polyester were determined. Fabric samples were placed over a single diameter cylinder to imitate the human leg. The aerodynamic resistance was acquired at different speeds relevant to high speed winter sports. Evaluation of comfort properties (liquid moisture transport in multi-dimensions) of each layer as well as a double layer was performed and the liquid moisture management capacity of the assembly was classified.
ABSTRACT The aerodynamic properties of 15 knitted fabrics of varying cover factor, yarn, and fibe... more ABSTRACT The aerodynamic properties of 15 knitted fabrics of varying cover factor, yarn, and fiber compositions were investigated for their aerodynamic properties on circular cylinders in a wind tunnel. Measurements of the drag force, pressure distribution, and the Particle Image Velocimetry (PIV) technique were used in order to obtain a better understanding of the effects of yarn, fiber composition, cover factor, and elastic deformation on the flow field and drag coefficient. It was clearly demonstrated from the drag force measurements that the yarn construction and fiber composition have a substantial effect on the drag coefficient (CD), with fabrics composed of spun yarn experiencing no CD-drop as opposed to those composed of filament yarn, and being almost unaffected by the cover factor in the range of Reynolds numbers investigated. Hairiness of the spun yarn was found to minimise the drag-reducing effect of the boundary layer transition and increase the trans-critical drag. The hairy surface layer also appeared to retard the turbulent boundary layer as almost no pressure recovery was observed prior to separation on the cylinder model. The effect of elastic deformation was investigated by image analysis of scanned textile samples, and demonstrated that surface roughness might not be directly correlated to cover factor when the fabrics are stretched. Different elastic behavior of fabrics with different cover factors was also found to affect the structure of the knit surface and thus their aerodynamic behaviour. The onset of drag crisis found in drag measurements confirmed the deviation from a sequence determined solely by cover factor.
The aerodynamic drag force acting on a circular cylinder clad with knitted wool and polyester tex... more The aerodynamic drag force acting on a circular cylinder clad with knitted wool and polyester textiles has been investigated in wind tunnel experiments in this study. Particle image velocimetry (PIV) was utilized to determine the flow field, both around the separation point and a wake profile in the close wake. The drag forces and the characteristic C D curves were determined over a range of Reynolds numbers expected to contain flow transition, for a number of knitted textiles having different surface roughness characteristics. The effects of knitting parameters and type of yarn on the flow field were investigated. The parameters of interest to be examined were critical Reynolds number, separation point, growth of the wake and wake profile. The wool and polyester textiles examined showed dissimilar effects on the flow field. Both were clearly adding surface roughness, and hence tripping transition to turbulence at a lower Reynolds number than for the smooth cylinder. The wool textile did however turn out be a more effective turbulence trigger than expected.
The paper addresses the effects of geometry and physical parameters of knitted fabric structures ... more The paper addresses the effects of geometry and physical parameters of knitted fabric structures on their aerodynamic and comfort properties. In order to evaluate whether significant aerodynamic and comfort advantages may be achieved by changing the ...
Wind tunnel testing has been carried out on nine-knitted single jersey fabrics (100% polyester) u... more Wind tunnel testing has been carried out on nine-knitted single jersey fabrics (100% polyester) using cylinder and leg models to determine its aerodynamic behaviour over a range of speeds (20-80 km/h) representative of sports activities. Strong correlation between fabric manufacturing (cover factor) and fabric roughness and aerodynamic parameters has been established. Similar aerodynamic behaviour of fabrics was observed when tested on the cylinder model and on the leg model.
In this paper, the double layer concept of knitted fabrics suitable for performance sportswear, w... more In this paper, the double layer concept of knitted fabrics suitable for performance sportswear, where each layer is separate from the other, was studied. Aerodynamic properties of this assembly, where the base layer is made of 100% wool and an external layer made of 100% filament polyester were determined. Fabric samples were placed over a single diameter cylinder to imitate the human leg. The aerodynamic resistance was acquired at different speeds relevant to high speed winter sports. Evaluation of comfort properties (liquid moisture transport in multi-dimensions) of each layer as well as a double layer was performed and the liquid moisture management capacity of the assembly was classified.
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