Meeting Abstract
Hammerhead sharks (Family Sphyrnidae) are characterized by a distinctive lateral expansion of the head known as a cephalofoil. The winghead shark, Eusphyra blochii, is the most ancestral member of this group with a high aspect ratio cephalofoil that is 40-50% of total body length. Computed tomography (CT) scans of a winghead shark were used to generate a computer model for performance testing using computational hydrodynamics. This model was tested at multiple angles of attack (pitch) and yaw to determine the velocities, forces, pressures, lift coefficients (CL), and drag coefficients (CD) generated by the winghead’s cephalofoil. Positive lift coefficients were identified as starting at an angle of attack of +5° and continuing up to +25°. The coefficient of drag was at its lowest at an angle of attack of +10°. These computer simulations were then evaluated using 3D printed models of the winghead shark cephalofoil submerged in a water tunnel and oriented at selected angles of attack to water flow. Digital particle image velocimetry (DPIV) was used to quantify fluid flow around the cephalofoil. Cross-correlation analyses of fluid flow identified velocity differences above and below the cephalofoil as well as at the end of the cephalofoil. Vorticity was also identified trailing the cephalofoil. While swimming level, the cephalofoil of the winghead shark has a natural angle of attack of about +17.6°. At this angle, there is slightly positive coefficient of lift while the coefficient of drag is near zero. However, as the winghead shark elevates or depresses its head (changing the angle of attack), lift and drag characteristics change in a way that is consistent between computer simulations of hydrodynamics and DPIV measurements of fluid flow.
