CFD-based simulation assessment of an artificial upwelling antibloom system for a salmon farming site

Abstract

The proliferation of microalgae, also known as microalgal bloom or Harmful Algae Bloom (HAB), is a damaging phenomenon for the correct functioning of salmon farming systems worldwide. Several anti-HAB systems have been developed and are currently being evaluated. One type of system is based on air diffusion from below the ocean surface where the fish farms are located. However, the configuration that would yield the highest efficiency of these systems has yet to be determined. In this work, the effectiveness of current and potential new anti-HAB systems configurations is assessed through computational fluid dynamics (CFD) modeling. The model of the section of the ocean and the air diffusion system was implemented in OpenFOAM representing the zone where the fish farm of Salmones Blumar S.A. is placed. The HAB is assumed to behave as a tracing substance, so the model becomes a three-phase system, which uses an Euler-Euler approach and a k-ε turbulence model, as well as stratified current velocities. The CFD model was validated with onsite data of water velocity at different water depths. Under these conditions, the configuration of the case study diffusers (i.e., 42 diffusers placed in two rows, with an average separation of 4 m between consecutive diffusers, and located 15 m deep) results in a 25 % decrease of the HAB penetration inside the farm. Additionally, placing the diffusers 5 m closer to the water surface increments the efficiency (i.e. HAB concentration reduction) of the system by 75 %, providing a cost-efficient solution, because the number of diffusers and their airflow remain unchanged.