A turbulent jet discharging into a motionless surrounding fluid is shown in the figure below

Figure 19.1 Turbulent Jet

Near the nozzle two single-stream mixing layers form on either side. The velocity discontinuity between the uniform velocity of the discharged flow and the surrounding motionless fluid form mixing layers. The vortices develop at the interface between the fast and slow moving fluid streams. At sufficient distance downstream of the orifice fully developed jet is established. The experiments show that the cross-stream distribution of the mean velocity acquires the self-preserving form

(19.1)

Here, and are x dependent, is the centerline velocity.