Mixing and entrainment in the near field of turbulent round jets

Results from experiments on the near field of a turbulent circular pipe jet at Reynolds numbers between 3,000 and 30,000 are compared to analytical models derived from assuming a perfect balance between axial and radial flow rates. This assumption is proved to be valid on average by taking measurements on both longitudinal and transverse planes and by direct evaluation of axial and radial flow rates. The experimental campaign is carried out by performing measurements by means of high-speed particle image velocimetry. The analytical models describe approximately the behavior of measured average radial velocities and entrainment rates with indications of a significant Reynolds number dependence which disappears for values larger than 10,000. This behavior is also confirmed by velocity rms and integral scale results.