Experimental and numerical study on the flow field of a bottom-supported net cage with double-layer fishing nets

This paper employs a combined approach of numerical simulation and experimental verification to evaluate the flow field characteristics around a bottom-supported net cage. The present study simplifies fishing nets into porous, permeable panels by setting appropriate coefficients for viscous drag and inertial resistance based on the porous medium method. Model tests are carried out in a flume to validate the numerical method. The study comprehensively analyses the impact of different factors on the flow field, including the effects of double-layer nets, net solidity and the combination of different solidities in inner and outer nets. The results show that doublelayer side nets help reduce downstream velocities and improve the uniformity of the downstream flow field distribution. When multiple cages are deployed in an array, the double-layer nets can mitigate the impact on the flow field of downstream cages to some extent. Increasing net solidity promotes velocity attenuation and enlarges the size of the low-velocity region. The solidity of the outer net mainly affects the downstream average velocity, and the solidity of the inner net primarily affects the wake characteristics. Results show that optimising the net solidity and the number of side nets is necessary to balance the flow field distribution for efficient water exchange.