Bioluminescence in sphere-generated turbulent wakes

Turbulent fluctuations generated in the wakes of simple bluff bodies are known to stimulate bioluminescence in marine microorganisms. The flow-induced stress experienced by the microorganisms is linked to their light emission behavior. This flashing behavior is influenced by several factors, including the species of the microorganism, its age, physiological state, as well as a variety of environmental variables such as water temperature and salinity. In this work, a basic bio-stimulation model is developed with the help of Large Eddy Simulations (LES), to recreate bioluminescence observed in field experiments of the unsteady wake of a spherical object. The Reynolds number is kept in the range of 10⁴ to 10⁵ for both the simulations and the experiments. The bio-stimulation methodology involves introducing tracer particles within the LES-generated flow field, and identifying potential stimulation sites for the tracers based on empirical bioluminescence data available in the literature, as well as data extracted from the field experiments. This modeling approach is designed to identify the fundamental flow variables that help trigger bioluminescence, specifically in terms of the spatial distribution of turbulent kinetic energy (TKE), the resolved stress, and the subgrid stress in the vicinity of the solid object. The temporal dependence of the light emission intensity is based on experimental data available for various bioluminescent organisms of interest. The benefits of using probabilistic light emission profiles, which account for physiological and environmental variables that can affect the organisms' responsiveness, are also explored.