Experimental approaches towards interpreting dolphin-stimulated bioluminescence

Area of Science:

• Fluid dynamics
• Bioluminescence
• Animal locomotion

Background:

• Previous anecdotal reports on dolphin-stimulated bioluminescence are conflicting.
• The absence of bioluminescence was often incorrectly assumed to indicate laminar flow.
• Hydrodynamicists lack evidence for laminar flow over most of a dolphin's body.

Purpose of the Study:

• To assess bioluminescence as a flow visualization technique for swimming dolphins.
• To relate plankton stimulation to fundamental flow characteristics.
• To investigate the relationship between boundary layer thickness and bioluminescence intensity.

Main Methods:

• Laboratory experiments with pipe flow and spheres.
• Computational fluid dynamics (CFD) modeling of an idealized dolphin.
• Intensified video recordings of gliding dolphins.
• Studies on forced separation and laminar-to-turbulent transition.

Main Results:

• Bioluminescent organisms stimulate in both laminar and turbulent flow above 0.1 N m-2 shear stress.
• CFD predicted suprathreshold shear stress on an idealized dolphin model.
• Bioluminescence intensity decreased with flow speed but increased with flow separation.
• Dolphin videos showed brilliant bioluminescence on the body, suggesting attached flow.
• Lack of bioluminescence on rostrum, melon, and fin leading edges correlated with thin boundary layers.

Conclusions:

• Flow-induced bioluminescence is a viable method for visualizing dolphin hydrodynamics.
• Bioluminescence intensity directly correlates with boundary layer thickness.
• The distribution of light reveals flow patterns, including attached flow and separation points.