This present work follows a series of experimental studies on thermosiphon flows. In order to numerically highlight these experimental studies, we realized a geometric model from a vertical cylinder open at both ends, including a heated heat source with imposed heat flow. This source is placed at the entrance of the cylinder. The vertical walls of the cylinder are maintained adiabatic. The confinement of the fluid inside the cylinder causes a suction of the fresh air from below and thus transfers a thermal power absorbed by the system. There is a thermosiphon flow around the thermal plume. The profiles of the dynamic and thermal fields have shown that the structure of a plume generated by a heated source is closely influenced, mainly by the properties of the flow around this source. During the vertical evolution of the thermal plume, we have identified three different zones: An area, used to supply the plume with fresh air, is distinguished by temperature and velocity profiles, a zone of development of the flow of the buoyancy effect characterized by temperature profiles having a maximum on the plume axis and an area where the profiles flatten out, thus reflecting the establishment of the flow. The results showed an improvement in the energy absorbed by the fluid and an increase in the volume flow rate of the flow inside the cylinder characterized by the recirculation of the fluid.