Mechanical Reproduction of Aerosols during Respiration of Bottlenose Dolphins*

To characterize the evolution of airborne droplets and flow field during exhalation and inhalation of bottlenose dolphins, we recorded and analyzed high-speed holograms for multiple breaths of trained dolphins at the National Aquarium in Baltimore. These results are being used as a reference for the design and calibration of a mechanism that mimics the dolphin breaths, for use in laboratory tests aimed at understanding the exposure and risk posed to marine mammals during and after an oil spill. The exhalation plume is reproduced by opening a high-speed valve at the exit of a 20L pressurized volume representing the lungs, and placing two aerosol generators, consisting of porous cylinders having pressurized liquid on their outer side, along the path of the air outflow. These generators are the primary source of small droplets and high-speed ejecta. The source of larger droplets and non-spherical blobs is the liquid on top of the exhalation valve, representing water in the dimple of a dolphin's blowhole after surfacing. The inhalation is simulated by opening another high-speed valve at the entrance of a second chamber in partial vacuum. The droplet statistics are recorded using high-speed holography, and the flow-field is resolved using PIV. The inhaled liquid is collected and monitored. Ongoing calibration tests involving clean water aim at reproducing the airflow and droplet statistics recorded in the aquarium. Subsequent tests will involve different oil and oil-dispersant mixtures.