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An Evaluation of Simplifying Assumptions in Dairy Cow Computational Fluid Dynamics Models

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 59(6): 1575-1584. (doi: 10.13031/trans.59.11908) @2016
Authors:   Mario R. Mondaca, Christopher Y. Choi
Keywords:   Animal-occupied zone, CFD, Dairy.

Abstract. Concurrent with the development of technologies and strategies for abating the heat buildup inside dairy barns, there is greater demand for an efficient and accurate way to test their performance. Computational modeling has improved to the point that it is now feasible to create realistic representations of animals to facilitate fluid dynamic modeling. Therefore, this study sought to use computational fluid dynamics to create and evaluate six different cow geometries: a sphere, a cylinder, a rectangular prism, a six-cylinder configuration, and two polygonal geometries labeled “low-polygon cow” and “high-polygon cow.” These six geometries were compared on the basis of their relative ability to replicate the effects of various different cooling and ventilation systems in operation inside a dairy barn. The low-polygon cow, having achieved results similar to the high-polygon cow with a coarser mesh, was then used to test the now common assumption that the area occupied by an animal (commonly called the animal-occupied zone) can be treated as porous media. While all three realistic geometries predicted heat transfer with nearly the same degree of accuracy (all were within 10% of each other), the test showed that key localized differences must be taken into account when selecting a particular geometry. The testing also found evidence in support of the assumption that an animal-occupied zone should be treated as porous media when evaluating the effects that the zone will have on the rest of the computational domain; however, the animal-occupied zone assumption should not guide any evaluation of the transport phenomena occurring within the zone itself.

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