Numerical simulation of the flow around fishing plane nets using the porous media model Yun-Peng Zhao a,n , Chun-Wei Bi a , Guo-Hai Dong a , Fu-Kun Gui b , Yong Cui c , Chang-Tao Guan c , Tiao-Jian Xu a a State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China b Marine Science and Technology School, Zhejiang Ocean University, Zhoushan 316000, China c Qingdao Key Laboratory for Marine Fish Breeding and Biotechnology, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China article info Article history: Received 21 February 2012 Accepted 5 January 2013 Keywords: Fishing plane net Flow field Porous media model Numerical simulation abstract A three-dimensional (3D) numerical model is established to simulate the flow field around fishing plane nets in a current. The realizable k–e turbulence model was chosen to describe the flow, and the governing equations are solved by using the finite volume method. In this model, the net is modeled using the porous media model. The unknown porous coefficients are determined from the hydro- dynamic forces on the net and from the flow velocities and the attack angles using the least squares method. In order to validate the numerical model, the numerical results were compared with the data obtained from two physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. This numerical model is applicable for the simulation of the flow field around a fishing net. Using the proposed method, this paper presents the flow field around a plane net with different plane net inclination angles, plane net heights, spacing distances between two plane nets and plane net numbers. This study provides information about the flow field around the fishing net cage. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction As the demand for seafood increases, the aquaculture industry is playing a more and more important role in the fish production industry. At present, the net cage is becoming prevalent in aquaculture industry around the world. The flow field inside and around the net cage is important both from an engineering perspective and from an ecological perspective. Numerous studies have shown that, the force on cage net is proportional to the square of the flow velocity. Even if small velocity differences exist, this may lead to great force differences. So in the investigation on the forces acting on the net cage, the flow velocity distribution around the cage net usually cannot be ignored. It is now generally accepted that water motion is beneficial for maintaining the water quality in the net cage and sufficient water exchange is important for the fish health and growth. However, too intense water motion may be disadvantageous to fish comfort. Further- more, the flow field characteristics determine the distribution of nutrients, refuse and dissolved oxygen in the net cage. Thus, the investigation on the flow field inside and around the net cage has become an important subject. To better understand the hydrodynamic fields of the net cage, extensive investigations have been carried out in the past dec- ades. Aarsnes et al. (1990) carried out a series of tests to study the velocity distribution within net cage systems, and velocity reduc- tion formulae for the net cages were developed. Li and Liu (1999) conducted a series of experiments to investigate the velocity distribution within a square fishing cage under four groups of different conditions, and obvious velocity reduction was found in the fishing cage. Fredriksson (2001) studied the flow velocity in an open ocean cage with field measurements, and an approximate 10% velocity reduction was found. Lader et al. (2003) conducted a series of experiments to investigate the forces and geometry of a net cage in uniform flow, and an average of 20% velocity reduction was measured inside the cage. Li et al. (2005) analyzed the shadowing effect of six practical gravity cage models by physical model tests, and the flow reduction coefficients within and downstream of the net cages were obtained. Johansson et al. (2007) performed field measurements at four farms in Norway, and major current reduction was measured in the current passing through the cages. The measured current reduction was between 33% and 64%. Huang et al. (2007) studied the flow velocity distribution behind a square cage using physical model tests, and the tests indicated that the fishing net had significant effects on the flow field outside the cage. Harendza et al. (2008) conducted experiments in a towing tank with particle image Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/oceaneng Ocean Engineering 0029-8018/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.oceaneng.2013.01.009 n Corresponding author. Fax: þ86 0411 84708526. E-mail address: zhaoyp18@hotmail.com (Y.-P. Zhao). Ocean Engineering 62 (2013) 25–37