Well-understanding indoor climate to ensure the comfort and well-being of the housed animals is important. Evaluation of the indoor climate for a naturally ventilated pig barn equipped with an indoor housing area and an outdoor exercise area is a challenge. Therefore, to accurately evaluate indoor climate for the special pig housing system, an open-source software OpenFOAM as a CFD simulation tool was used in this study. First, to ensure an accurate CFD model for the simulation of airflow pattern, different mesh sizes and 5 turbulence models (k-ɛ, RNG k-ɛ, realizable k-ɛ, k-ω, k-ω SST) were tested. Then, seven cases with different wind directions (0°, 30°,?150°, 180°) perpendicular to the sidewalls and two cases of pig barns with/without an exercise yard were simulated and assessed by indoor airflow pattern and ventilation rate. It is a preliminary study, and the results contribute to a better understanding of the airflow pattern inside the naturally ventilated pig barn with an outdoor exercise yard in relation to different wind directions and barn geometries.