Study concerning a double skin flow with secondary ventilation was conducted numerically, in order to understand the basic mechanisms of the free convection in an open channel asymmetrically heated with uniform heat flux density (510 W/m2). The vertical channel corresponds to a double skin façade, which was immersed in a tank filled with water. The tank corresponds to the environment which allows us to overcome pressure conditions at the inlet and the outlet of the channel. The use of water allows neglecting radiation effect. The mass conservation equations of momentum and energy are solved using the finite volume method and numerical simulations are performed using Ansys Fluent CFD software. Our interest, in this work, is the study of the influence of the position and the size of an opening in the adiabatic wall, which represents secondary ventilation, on the flow dynamics and the heat transfer.