1) Change boundary into a wall => this will create a coupled wall (wall/wall-shadow) 2) Type the following TUI command : mesh/modify-zones/slit-face-zone => this will uncouple the walls 3) Choose appropriate external boundary for each wall External boundaries are : pressure inlet / outlet, velocity inlet, outflow, mass-flow inlet, pressure far field, wall, symmetry, axis, periodic, inlet /outlet vent, intake / exhaust fan Internal boundaries are : fan, interior, porous jump, radiator and wall