General rules for the pressure loss of flow across wire screens and simple fabrics are devired herein from the available test data. At higher Reynolds numbers the results obtained agree satisfactorily with the Borda-Carnot theory, which considers the dynamic losses to be due to a sudden expansion of the cross section behind the openings of an obstacle. On the other hand, at very low Reynolds numbers the pressure loss seems to be proportional to the velocity, corresponding to the Hagen- Poiseuille kind of flow. In the intermediate range of the Reynolds number the loss coefficient is found by statistical analysis to be a function of this number and the solidity ratio of the material.
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References
1.
Theoretical and experimental data on the flow through nozzles can be found in engineering handbooks.
2.
(b) The Borda-Carnot loss of pressure can be found in the literature on diffusers.
3.
(c) Drag coefficients can be found in handbooks, such as Hoerner, "Aerodynamic Drag," 1951.
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Eckert and Pflueger, Tests Concerning the Pressure Loss of Various Round-Wire Screens, Luftfahrt-Forsch. p. 142 (1941); Trans. Natl. Advisory Comm. Aeronautics, Tech. Memo.
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Flachsbarth, "Drag of Various Screens," Vol. IV, Goettingen, Germany, Ergebnisse Aerodynamische Versuchsanstalt , 1932.
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Longnecker, Air Flow Through Woven Materials, M.S. Thesis, Lowell Textile Institute, Lowell, Mass., June 1950 .
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Rainard, Air Permeability of Fabrics, TEXTILE RESEARCH JOURNAL17, 167 (1947).
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Schubauer, Spangenberg, and Klebanoff, Aerodynamic Characteristics of Damping Screens, Natl. Advisory Comm. Aeronaut. Tech. Note 2001 (1950). (Generally, this source gives ζ values which are lower than from any other reference.)
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Simmons and Cowdrey, Measurements of the Aerodynamic Forces Acting on Porous Screens, Aeronaut. Research Comm. (England) RM2276 (1945).
