Passive control of the entrainment phenomenon in the turbulent jets is a
mixing enhancement economical method of wide interest in the industrial
field. A lobed nozzle without lobes inclinations allows improving mixing in
the generated flow compared to a reference circular jet. A second lobed
nozzle, having the same exit plane geometry but with inclined lobes
intensifies, in a considerable manner, the entrainment which reaches up to
four times the one in the reference circular jet. The lobed jets vortical
dynamics analysis shows that the azimuthal structures are not annular like
in the case of a circular jet, but discontinuous, due to the shear of the
transverse flow induced by the curvature variation of the exit plane. The
streamwise structures development at the discontinuities locations is
probably explaining the entrainment benefit observed in the lobed jet
without inclination angles. The lobed jet issued from the second nozzle
presents like the first lobed jet, discontinuous azimuthal structures, but
its remarkable induction benefit is not merely owed to the previous
phenomenon. The intensification and organisation of the streamwise vorticity
field into large scale structures, resulting in a consequent mixing
enhancement, are connected to the increased shear produced by the lobes
inclinations.