Influence of angle of attack on hydrodynamic performance and its implications for designing semi-mobile aquaculture structures: A CFD study

This study examines the influence of various angles of attack of current flow (0° to 90° with 10° intervals) on the hydrodynamic performance, surface shear stress and drag force of various designs of semi-mobile aquaculture structures. The structures were cylinder- and cone-shaped, with the porosity on the body varying from 0 % to 15 %. Computational Fluid Dynamics (CFD) was employed, and the modelled flow speed and drag force were validated with flume-based experiments on a scaled model, 2.16 m in length and 0.45 m 3 in volume. It was found that when the angle of attack was 30° and 60°, flow acceleration, from 1 to 1.3 m s − 1 , and low-speed zones (<0.1 m s − 1 ) occurred in the cylinder-shaped structure with an impermeable body (design 1A). However, flow speed was relatively uniform in the cone-shaped structure with porosity of 15 % (design 2A). When the angle of attack was 90°, flow speed in the structure increased from 0 m s − 1 in design 1A to 0.4 m s − 1 in design 2A. This indicated that hydrodynamics in design 2A could be more beneficial for fish welfare (increased water flow maintains dissolved oxygen) than design 1A, particularly during oblique flow conditions. However, the drag force exerted on design 2A is greater than those on design 1A. These differences in drag force increase when the flow speed increases and the volume of the structure increases, which could increase the operational costs. Overall, the findings of this work imply that designing aquaculture structures that benefit both fish and farmers is challenging, and balancing fish requirements with operational costs is crucial to select appropriate designs. • A novel design for aquaculture structures to maximise fish welfare is proposed • Angle of attack and structure design strongly influences the hydrodynamics • The trade-off between the basic and the novel design is discussed