The aerodynamic roughness of textile materials

Experiments were performed in a low-speed wind tunnel to study the effect of textile roughness on the aerodynamic flow around a circular cylinder. The circular cylinder is fitted with different fabric samples on the outer surface. For each of the fabric samples, the drag force and the mean pressure on the circular cylinder are measured. Based on the data obtained, the critical transition range with respect to the Reynolds number is identified for comparison. The surface roughness of each fabric sample is examined using a laser scanning microscope. The roughness is then represented by a quantity named S10z, which is defined according to ISO 25178. Consequently, based on the wind-tunnel data and the textile roughness information, further discussion is made with regard to the roughness of the textile material and the Nikuradse’s sand-grain roughness, ks, which characterizes the aerodynamic roughness. Examining the empirical relationships that are proposed in the literature concerning variations of th...