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Experiments on Drag of Revolving Disks, Cylinders and Streamline Rods at High Speeds

出版	National Advisory Committee for Aeronautics, 1944
URL	http://books.google.com.hk/books?id=3JcV6BFGQaQC&hl=&source=gbs_api

註釋Summary: An experimental investigation concerned primarily with the extension of test data on the drag of revolving disks, cylinders, and streamline rods to high Mach numbers and Reynolds numbers is presented. A Mach number of 2.7 was reached for revolving rods with Freon 113 as the medium. The tests on disks extended to a Reynolds number of 7,000,000. Parts of the study are devoted to a reexamination of the von Kármán-Prandtl logarithmic resistance law and the Ackeret-Taylor supersonic drag formula and conditions for their validity. The tests confirm, in general, earlier theories and add certain new results. A finding of first importance is that the skin friction does not depend on the Mach number. Of interest, also, are experimental results on revolving rods at very high Mach numbers, which show drag curves of the type familiar from ballistics. A new result which may have general applicability is that the effect of surface roughness involves two distinct parameters, particle size and particle unit density. The particle size uniquely determines the Reynolds number at which the effect of the roughness first appears, whereas the particle unit density determines the behavior of the drag coefficient at higher Reynolds numbers. Beyond the critical Reynolds number at which the roughness effect appears, the drag coefficient is found to be a function of unit density. In the limiting case of particle "saturation," or a maximum density of particles, the drag coefficient remains constant as the Reynolds number is increased.