Reliability of turbulence models and mesh types for CFD simulations of a mechanically ventilated pig house containing animals

Abstract

The use of computational fluid dynamics (CFD) to study the airflow within farm animal buildings is increasing. The choice of turbulence model within CFD is generally considered to be important due to the approximations of the turbulence in varied scales. Although some studies have been conducted on evaluations of turbulence models in simulation of airflow in ventilated rooms, knowledge of airflow in the animal occupied zone (AOZ) with airflow blockage by the animals and knowledge of thermal convection effects are still limited. In this study, five commonly used two-equation turbulence models (standard k – ɛ , realisable k – ɛ , RNG k – ɛ , standard k – ω , and SST k – ω ) were applied to a CFD model of the airflow in a mechanically ventilated pig room with animals housed in pens. In addition to turbulence models, the effects of non-conformal meshing which combines several computational sub-domains and connects the boundary of domains using interfaces, were tested. The effect of mesh ratio on the interface (i.e. ratio of the grid number of the up and down interface) was studied based on fully structural hexahedral mesh (SH). The investigation of mesh type effect was conducted by application of an unstructured tetrahedral mesh (UT) in the AOZ and SH in the rest of the domain. The results showed that the choice of turbulence model did not have a strong effect on the main airflow pattern except for the RNG k – ɛ model. The tested ratios of resolution at interfaces were also found not to strongly impact on the predicted airflow distributions. The use of UT in the AOZ sub domain also provided acceptable results. It was concluded that non-conformal meshes are a feasible alternative for animal buildings with complex geometries to maintain affordable grid numbers and also reduce the difficulties in mesh generation.