Meeting Abstract
By including the largest vertebrates to have ever lived, baleen whales (Mysticeti) represent a group of highly-streamlined marine mammals that has achieved efficient, low-drag locomotion. High swimming efficiency by cetaceans has been confirmed, so far, by estimates based on flat-plate drag empirically corrected for body fineness ratio effects that increase drag via the turbulent wake. As useful as it may be, the approach is silent on the role of body shape and size in determining the relative importance of viscous friction, versus the pressure drag that result in the near-wake. We present the results of a Computational Fluid Dynamics (CFD) study of the flows and drag generated by several mysticete species, including 11 and 22m blue whales (Balaenoptera musculus), 14m humpback (Megaptera novaeangliae), 9m minke (B. acutorostrata) and 12m grey (Eschrichtius robustus). The simulations and analysis were carried out with the SC/Tetra commercial software. The whale models were obtained from the 3D-scanning of anatomically realistic figurines. The results, which are specific to rigid (gliding) bodies, were corrected with a new semi-empirical tail-heaving drag factor accounting for active swimming effects. It is shown that for these swimmers, viscous friction is the dominant source of drag (about 75%) over pressure drag (25%); that total drag per body area is rather insensitive (down to about 10-15%) to body shape and tail vertical taper within and across species; and that the unsteady drag generated by the caudal peduncle effectively doubles the drag coefficient, in comparison to rigid body drag.
