This paper presents a numerical investigation of airflow in an open geometry. The case under consideration is a room with two opposite and decentred openings which create a strong potential for ventilation. The building's characteristic dimensions are the following: H=2.50 m height and W=6.50 m width. A temperature difference between the walls and the outside air is fixed, resulting in a characteristic Rayleigh number (Ra) ranging from 105 to 107. This room model proceeds from a benchmark exercise "ADNBATI" (http ://adnbati.limsi.fr) coordinated by the"Centre National de la Recherche Française -CNRS-".