Some characteristics of pulsating or flapping jets

Axisymmetric jets subjected to large amplitude pulsations and plane jets forced to flap about a mean direction have been investigated experimentally. Both types of forcing increase the jet entrainment in the initial region but while the pulsating jet relaxes into the same axymptotic regime as the unforced flow the expansion of the plane flapping jet is affected far downstream. This behavior may be accounted for by the induced pressure gradient. The periodic motion is at first amplified and then decays in both cases. The turbulent intensity in the initial region grows more rapidly than in the corresponding unforced jets and overshoots the asymptotic level. Some properties of the periodicmotions are analysed and compared with predictions of stability calculations.