Flow Through Fabric-like Structures

Abstract

A method is presented for the visual investigation of flow through fabrics. The fabric pores are considered as orifices, and the effect of weave structure on the fluid flow is investigated in the range of Reynold's numbers 10 to 400. For this investigation, a liquid is forced past models representing the four possible combina tions of yarns in a woven fabric interstice, and the fluid motion is visualized by using air bubbles, which are detected by means of a suitable light source, as the distinguishing medium. Since both the fluid and the construction material for the models and viewing chamber are translucent and possess the same refractive indices, it is possible to obtain uninterrupted, undistorted visualization of the fluid flow through and past the fabric-like structures. Visual and photographic investi gations of the flow are made in various significant planes normal to the fabric-like structures, or parallel to the direction of flow. The resulting photographs are analyzed and interpreted to provide information concerning the effect of fabric construction and variation of Reynold's num ber on the area available for the passage of fluids through each pore type, or the so-called "effective pore area." It is shown that the four pore types do not behave like geometrically similar orifices, so that for a given diameter/pitch ratio the effective pore area is not the same in all cases. This area decreases with increasing Reynold's number. Except at very low Reynold's numbers, the effec tive pore area proves to be less than the actual minimum pore area, but greater than the pro jected area, with the exception of the plain-weave pore type. Assuming a minimum cross- sectional pore area, as determined by graphical analysis, it is shown that the effective pore area/minimum pore area ratio is almost a constant for all four pore types of the models tested at a Reynold's number of 400.