Abstract
The aerodynamic properties of a tuft of fibers are considered not a little different from those of a solid body similar in shape and of an ordinary porous body. The factors which cause the differnce may be as follows : (1) the properties of a fiber itself and (2) the stream—passing through or around a tuft—caused by its surface structure, compressibility and porosity. On the basis of this conception we have for years investigated this problem via air drug coefficient and clarified the effects of the surface structure on the air drug coefficent by the use of three kinds of experimental models-i.e., pingpong balls, rough balls pasted with sand grains on their surface and tuft balls pasted with fibers.We have measured air flows around these three kinds of models independently minutely, clarified properties of these air flows on these models, and finally looked into what the relation between them is. The results obtained are (1) the values of air drug coefficient of a pingpong ball and rough balls are roughly equal to those of a smooth sphere, (2) the values of tuft ball are about twice as large as those of pingpong ball and rough ball, (3) the wake in case of a pingpong ball equals the one of rough ball and the wake of tuft balls is clearly greater than those of pingpong ball and rough ball and (4) the relation between the air drug coefficient and properties of flow around each model can be qualitatively made clear.
