Clothing Fabric Air Friction Model And Its Impact Factor Research

In cycling competition, in order to achieve better results, the most important way is to improve speed. And reducing the resistance in the process of movement, can ascending movement speed to a great extent. So the aerodynamic experts tried as far as possible to reduce resistance which aspects encountered in the process of moving. There are some scholars studied the garment’s aerodynamic performance made of different fabrics. But most of these scholars used Air Resistance Formula in their study, and the air resistance in this formula mainly includes the shape resistance, mechanical collision resistance and air friction resistance. Only air friction resistance is affected by the fabric surface topography. But considered that, at present, there isn’t an exact evaluation indicator to measure drag reduction effectiveness of fabric surface that is fabric’s wind resistance performance in study of drag reduction on the surface of a garment. So on the basis of analyzing the stress factors in the process of cycling sports, this paper put forward the index:f-the fabric air friction resistance coefficient in order to provide a standard to measure fabric’s wind resistance performance. At the same time, this paper studied the wind resistance performance of different fabric and its impact factors, and tried to find out the intrinsic principle.There are five main conclusions of this subject:(1) According to the principle of aerodynamics and deduced from the related formula, the fabric air friction model is set up: P=f·ρ·vnAmong them:P is differential pressure/(Pa);f is air resistance coefficient, it’s dimensionless. The smaller the numerical is, the better the fabric wind resistance performance; ρ is air density (kg/m3), v is wind speed (m/s).(2) According to the known condition, the structure characteristics of the model were analyzed, then the reasonable mathematical methods and algorithms were chosen. Finally, the model can be solved by combining with the experimental data and the VB programming. The main task of VB programming is solving the unknown parameters n in the mathematical model and calculate the air friction resistance coefficient f of fabrics. This paper used search method to solve the model, and used the least squares fitting criterion to calculate fabric’s air friction resistance coefficient. Finally test of goodness of fit was used to terrify the model and sample data.(3) Wind tunnel experimental design. In this paper, design scheme of wind tunnel experiment is:the fabric was tiled on the self-made tablet, fabrics edges were fixed to prevent sliding around. Placed the tablet in wind, tunnel, the fabric’s warp direction is parallel to the direction of air flow. Using Testo-425 thermal anemometer to measure wind speed on the surface of the fabric under different environment wind speed.(4) Solving the fabric air friction resistance model and its validation. After optimizing the solving scheme, the solution of the model has good representation. n=2, so the air friction resistance optimization model of fabric surface is: P=fpv2Carrying on the test of goodness of fit by statistic R2 between fabric air friction model and the sample data. The results showed that the goodness of fit between the model and the sample data is very high, all above 0.99. So the model has highly reliability. The model can be used to measure and calculate the wind resistance performance of fabric in the future.(5) The bigger the fabric’s evaporation rate, the lower the fabric air friction resistance coefficient, the better the performance of wind resistance. Most fibers with high evaporation rate such as CoolMax belong to synthetic fibers. From the electron microscope scanning figure we can see that fiber has smooth surface and less defect. The fabric surface weaved with this fiber is flat and with less yarn breaking.When the mixed raw material is same, air friction resistance coefficient f will increase with the increase of cotton fabric’s proportion. When the mixed ratio is 100:0,f coolmax<fnylon<fmodal, namely CoolMax pure yarn fabrics has the best wind resistance performance, nylon fabric is second, modal fabric’s wind resistance performance is the worst. Therefore when designing sport clothes, designer can choose 100% CoolMax fabric to get better drag reduction performance. For it can get better wind resistance performance and good moisture absorption performance.The aerodynamic reason of causing this phenomenon is:When the mixed ratio is 100:0, fabrics are weaved by the same kind of yarn. So the concave and convex effect of the organizational structure is even and neat. As there is an obvious vortex in the bottom of the pit, the air at the upper part of the vortex has the same direction with the wind direction, the air at the bottom of the vortex has reverse direction with the wind direction. Pit external fluid is sliding friction, pit internal fluid is rolling friction. Vortex cushions effect turned sliding friction into rolling friction, so the fluid’s viscous resistance is reduced through the of pit wall, eventually friction resistance is reduced. When percentage of cotton increased, as the cotton fiber surface has many small villi with irregular distribution, it can advance the turning point form layer flow to turbulent flow, thus the fabric air friction resistance coefficient is increased.The research of this paper provided a reference index for measuring the wind resistance performance of fabric. And the fabric air friction model can provide a calculation method to calculate fabric’s air friction resistance coefficient in the future. The research about the effect factors of wind resistance performance of the fabric can provide a certain reference for design of low wind resistance of fabric in the future.