DRAG COEFFICIENTS OF SWIMMING ANIMALS - EFFECTS OF USING DIFFERENT REFERENCE AREAS

The drag coefficient (CD) is useful for comparing the hydrodynamic drag among different swimming animals, but CD is calculated using an arbitrary reference area for which there is no uniform convention; both total surface area ("wetted are') and maximum cross-sectional area ("frontal area') are widely used. Drag measurements from 2 isopod species were used to calculate CD based on both wetted and frontal areas. Idotea wosnesenskii had a higher mean CD based on wetted area (0.084) than Idotea resecata (0.059), but a lower mean CD based on frontal area (0.95) compared to I. resecata. Reporting both wetted area and frontal area CD's should be done wherever practical. -from Author