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Velocity Deficits in the Wake of Lemon Shark Dorsal Fins Measured with Particle Image Velocimetry
Abstract Aquatic animal’s morphology provides inspiration for human technological developments, as their bodies have evolved and become adapted for efficient swimming. Lemon sharks exhibit a uniquely large second dorsal fin that is nearly the same size as the first fin, and this trait is of interest for investigation as to its hydrodynamic role. This experimental study looks at the drag forces on a scale model of the Lemon shark’s unique two-fin configuration in comparison to drag forces on a more typical one-fin configuration. The experiments are performed in a recirculating water flume, where the wakes behind the scale models are measured using particle image velocimetry. The experiments are performed at three different flow speeds for both fin configurations. The measured instantaneous 2D distributions of the streamwise and wall-normal velocity components are ensemble averaged to generate streamwise velocity vertical profiles. In addition, velocity deficit profiles are computed from the difference between these mean streamwise velocity profiles and the free stream velocity, which is computed based on measured flow rates during the experiments. Results show that the mean velocities behind the fin and near the fin tip are smallest and increase as the streamwise distance from the fin tip increases. The magnitude of velocity deficits increases with increasing flow speed for both fin configurations, but at all flow speeds, the two-fin configurations generate larger velocity deficits than the one-fin configurations. Because the velocity deficit is directly proportional to the drag force, these results suggest that the two-fin configuration produces more drag.
Faculty Advisor: Erin Hackett, Coastal and Marine Systems Science
Graduate Student Mentor: Vivian Turner, Coastal and Marine Systems Science
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