AbstractAn interferometric investigation has been conducted on open-cavity natural convection. The test section consists of three uniformly heated cavity plates and two partially heated outside walls. The cavity is gradually turned from sideways to upright at a constant Grashof number. For the side-facing aperture, Grashof number effects are also investigated in a limited range. At this zero inclination, boundary-layer-type flows are clearly formed. As the cavity inclination increases, substantial changes occur in local heat transfer. Gravity-drawn cold air acts as a promoter of heat transfer; however, at a large inclination, plume rise and cavity recirculation act as inhibitors. The overall average Nusselt number is less sensitive to the cavity orientation. It attains a maximum value at an inclination angle between 30° and 60°.