# Numerical Simulation of Airflow Distribution in a Pregnant
###### Abstract
Wind tunnel and scale model experiments are widely used in aerodynamic research, but they must meet similarity criteria such as for geometric, boundary, and Reynolds number [25] similarity, which requires additional time and cost. With the development of computational science, the complex flow interaction and flow field distribution observed in animal buildings can now be more comprehensively simulated [30]. Computational fluid dynamics (CFD) simulation provides an alternative method to overcome the shortcomings of traditional tests, scale models, and wind tunnel tests, and it has been widely used in the analysis of livestock buildings [31; 32; 33]. [PERSON] et al. used CFD to simulate the distribution of airflow and temperature in chicken coops and found that the uniformity of airflow and temperature distribution increases with an increase in air inlet position and distance from the chicken coop, but the range of influence on the environment inside the coop was limited [34]. [PERSON] et al. [35] used CFD to predict the airflow distribution in piggeries with comparison of five turbulence models and found that the applicability of the turbulence model depends on the specific situation. In the majority of the CFD studies on livestock buildings, the presence of animals is generally ignored [36; 37]. However, they may significantly affect airflow patterns as well as temperature and concentration profiles. Therefore, it is necessary to include the animals in such studies, as this is closer to real situations. Some researchers have conducted CFD simulations of livestock buildings, including detailed pig models of realistic sizes [38]. However, detailed pig modeling has not yet been applied to CFD simulations of the great numbers of pigs in commercial piggeries because ordinary desktop or professional workstation computers do not have the computational power necessary to handle such simulations with their extremely high grid numbers [33]. Therefore, simplification has been applied in which parts of the pig body such as the tail, ears, and legs are omitted from the model to save computational costs while maintaining simulation accuracy [39]. A simplified pig model has been used to establish a prediction model of air velocity in animal-occupied areas by omitting some pig components in a simulation study of the convective heat transfer between pigs and their surroundings [35]. However, simplified pig models where small parts have been omitted still produce high mesh numbers, leading to heavy calculations or poor mesh quality due to the irregular shape of the pig used to reduce mesh numbers. Therefore, simple geometric models have been adopted to further replace simplified models, such as cylinders, ellipsoids, and spheres [38; 40]. [PERSON] et al. investigated the convective heat transfer coefficients of chickens using CFD simulation and showed that similar coefficients were obtained when using spheroid and simplified chicken models [41]. [PERSON] et al. found that the average heat flux of cows could be adequately simulated through an assembly of spheres, cylinders, and six cylinders [42]. [PERSON] et al. compared an actual pig model with a cylindrical model, and the results showed that the convective heat transfer coefficients of the two models were strongly correlated [43]. Therefore, simplifying the individual pig to a regularly shaped object is effective as computational efficiency and accuracy can be ensured. In this study, a CFD model of a pregnant sow piggery with centralized ventilation was constructed for simulation and analysis of the airflow distribution with determination of the distribution of temperature, humidity, and airflow velocity. This study has certain significance as a reference for the structure and flow field optimization of pregnant sow piggeries.