A General Correlation of Friction Factors for Various Types of Surfaces in Crossflow

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Abstract
This paper is the elaboration of an unpublished one by the late E. S. Davis and A. Y. Gunter, which was released only to the National Advisory Committee for Aeronautics. The present work, using the friction-factor correlation proposed for bare tubes by Davis and Gunter, demonstrates its merit as a general method for correlating on a single line, pure crossflow friction over both bare and extended surfaces. This result is made possible through the use of an equivalent volumetric hydraulic diameter Dv, in both the Reynolds number and the ordinate, plus configuration ratios of the form (Dv/ST)n and (SL/ST)n in the ordinate. Friction factors for bare tubes of diameters from 0.02 in. to 2 in. are included, with transverse and longitudinal pitches ranging from 1.25 to 5 diam. Extended-surface crossflow friction reported on herein covers external round and square cross fins, both meshed and unmeshed, finned cylinders, radiator core-type surface, and one sample of internal wire-mesh fins. It is shown that flat plates and core-type surface with turbulence promoters do not correlate well on the proposed curve.

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