Effect of bottom drain positions on circular tank hydraulics: CFD simulations

Abstract

Moving the bottom center drain toward the tank wall in a large circular culture tank can make labor for fish harvest and tank maintenance much easier. But the bottom eccentric drain is rarely used. In this work, computational fluid dynamics simulations were carried out to compare the bottom eccentric drain tank with the bottom center drain tank, both originated from the same circular tank, by using FLUENT. Not only rotating flow by tangential water injection but also non-rotating flow by low waterfall inlet was considered. Eight tank models with two diameters were selected. Model validation was carried out by comparison with measurements. Velocity properties and mixing rates were larger in the center drain tanks than in the eccentric drain tanks in the rotating flow, while those are similar in both the tank configurations in the non-rotating flow. The hydraulic behavior of a dual-bottom-drain tank with both the center/eccentric drains was more similar to that of the eccentric drain tank in the rotating flow. One way to reduce the labor requirement in large circular tanks with the tangential water inlet, while keeping the center drain’s advantages, is to adopt the dual-bottom-drain tank design. By contrast, for the circular tanks with the low waterfall inlet, the eccentric drain tank design can be a good alternative to the popular center drain tank design.