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Drag Coefficients of Swimming Animals: Effects of Using Different Reference Areas
David E. Alexander
Vol. 179, No. 2 (Oct., 1990), pp. 186-190
Published by: Marine Biological Laboratory
Stable URL: http://www.jstor.org/stable/1541768
Page Count: 5
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The drag coefficient ( C D) is useful for comparing the hydrodynamic drag among different swimming animals. However, C D is calculated using an arbitrary reference area for which there is no uniform convention; both total surface area ("wetted area") and maximum cross-sectional area ("frontal area") are widely used. The choice of reference area can have a profound effect on calculations of drag coefficient. To illustrate this problem, drag measurements from two isopod crustacean species were used to calculate C D based on both wetted and frontal areas. Idotea wosnesenskii had a higher mean C D based on wetted area (0.084) than Idotea resecata (0.059), but a lower mean C D based on frontal area (0.95) compared to I. resecata (1.22); both differences are statistically significant. Given that there is no powerful hydrodynamic basis for choosing either reference area, and that conversions between wetted area C D and frontal area C D cannot accurately be made for complex shapes, I suggest reporting both wetted area and frontal area C D's wherever practical.
Biological Bulletin © 1990 Marine Biological Laboratory