Meeting Abstract
Baleen whales (Mysticeti) are a group of marine mammals that travel across oceanic basins in order to migrate between foraging areas and breeding grounds, thereby incurring high total energetic expenditures. These costs are minimized, mostly by a high degree of body streamlining which enables efficient, low-drag locomotion. Calculating the latter becomes a crucial element towards understanding the larger story of metabolic locomotor costs. As cetacean propulsion can be characterized by swimming modes ranging from carangiform to thunniform, drag generation is decoupled from propulsion by the flukes (Fish & Rohr 1999) and allows the evaluation of low-swim speed drag coefficients from rigid body steady-state hydrodynamics. Over the past decades (e.g. Webb 1975, Kooyman 1989), calculations of the drag generated by baleen whales and their sister taxon (Odontoceti) have used a correlation based on tunnel test data collected on blimps and airships (Hoerner 1962). We have used Computational Fluid Dynamics (CFD) to revisit – and re-confirm – Hoerner’s old equation relating drag coefficient to body length-to-width ratio, by using digital reconstructions of the HMA R100 airship of the late 1920’s, along with other profiles of differing fineness ratio (3 to 36). A comparison of these results was also carried out with CFD data of (gliding) rorqual drag, and showed agreement within 20% over the fineness ratios found in the field. The differences are traced from the enhanced pressure drag generated by the details of rorqual body shape, including those of the head and tail taper among other features.
