Hydrodynamics of octagonal culture tanks with Cornell-type dual-drain system

J.M.R Gorle,B.F Terjesen,S.T Summerfelt

doi:10.1016/j.compag.2018.06.012

J.M.R Gorle, B.F Terjesen + Show 1 more

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https://doi.org/10.1016/j.compag.2018.06.012

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Abstract

Large culture tanks of several hundred or thousand m3 size are generally encouraged for economic advantages in Recirculating Aquaculture Systems (RAS). Out of numerous possibilities in designing the inlet and outlet configurations in octagonal culture tanks, the inlet pipes near the corner walls and the outlets at the tank’s center and/or on side wall are some of the widely-used configurations. The use of wall drain to achieve a controlled flow pattern in the tank, however, influences distinct flow features such as pressure, velocity, uniformity and turbulence in the tank, which are of theoretical interest as well as practical importance. A finite volume description of the flow in an octagonal culture tank at full-scale was therefore developed using Realizable turbulence model with second order accuracy in space and time. The tank was equipped with an inlet pipe near the corner wall and dual-drain outlet system of Cornell-type. The base case had a flow configuration of 45% of flow through central bottom drain, and the rest through the wall drain. Model verification was performed using grid convergence tests, and validation was conducted using Acoustic Doppler velocimetry (ADV) based velocity measurements. The effect of wall drain on the large-scale and small-scale turbulent structures was studied using the distribution of turbulent kinetic energy and vorticity respectively. The parametric study on the flow-split between the two outlets was analyzed using different flowfield indicators, such as flow velocity, uniformity, vorticity strength, maximum absolute vorticity and swirl number. Such an inclusive analysis not only explores the hydrodynamics in the commercial culture tanks with Cornell-type dual-drain but also recommends the farmers with the suitable flow-split between such outlet systems.

Highlights

In the seeking of disease prevention, increased production rates and environment preservation, Recirculating Aquaculture Systems (RAS) have been in limelight to exercise a controlled rearing system (Dalsgaard et al, 2013; Summerfelt et al, 2016)
Unlike the aforementioned studies, which were largely limited to the examination of global flowfield, the present study focused on the evolution of large-scale and small-scale turbulent flow structures and the effect of dual-drain system on them
The Acoustic Doppler Velocimetry (ADV) based velocity measurements could offer an empirical base to validate the computational findings, the experimental setup itself contributes to measurement errors and uncertainties, which is usual in most industrial systems with complex flow patterns

Summary

Introduction

In the seeking of disease prevention, increased production rates and environment preservation, Recirculating Aquaculture Systems (RAS) have been in limelight to exercise a controlled rearing system (Dalsgaard et al, 2013; Summerfelt et al, 2016). In addition to creating a healthy environment, it is possible to exert some control over the flow domain in circular-type tanks used RAS facility, which plays a critical role in fish growth and the production and financial benefits. Previous studies have determined that the rotational velocity about the perimeter of circular tanks is strongly dependent upon the impulse force of water flow injected tangentially into the circular-type tank (Tvinnereim and Skybakmoen, 1989; Paul et al, 1991; Davidson and Summerfelt, 2004; Oca and Masalo, 2013; Venegas et al, 2014; Plew et al, 2015; Prabhu et al, 2017; Gorle et al, 2018). Rotational velocities close to the center of circular-type tanks are associated with the impulse force exiting the center of the tank, i.e., dependent upon the surface loading rate at the center drain (Davidson and Summerfelt, 2004). The inlet and outlet impulse forces are balanced by the forces created by drag on the fish and tank walls and floors (Plew et al, 2015)

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