If a flow with a low thickness and high velocity enters a lower velocity fluid, the field of this interference is
called jet stream. In the present manuscript, because of the importance of the turbulent co-axial jets, a
numerical study is done on this kind of jets. In many jet systems, a high-speed fluid from a circular nozzle and
a secondary fluid from a ring shaped nozzle co-axial with first nozzle at a lower speed is discharged into the
tube. These two flows are mixed inside a tube and form a single stream. In this manuscript, in order to study
the behavior of coaxial jets, the results of the computational fluid dynamics (CFD) are presented to determine
the place of secondary inlet position on the suction ration. For this aim, different secondary inlets were
simulated numerically by Computational Fluid Dynamics (CFD) software i.e. FluentTM. The obtained results
showed that the appropriate place to create the secondary inlet is near the first inlet i.e. for the △r/r = 0.6,
one can achieve the highest amount of suction ratio in the jet. In addition the present CFD results were
compared to the available experimental data which shows a good agreement.