Abstract
Axisymmetric jets have been observed to investigate the effect of controlled pulsation on the behavior of vortex rings by using the hydrogen bubble technique and hot-film measurement. Pulsed jets had similar velocity profiles in the initial region and in the fully developed region. This similar velocity profile was coincident with that in natural jets. The differences between the two kinds of jets in volume rate, in decay of centerline velocity and in distribution of turbulent intensity, were observed to be remarkable in the initial region. Such differences were caused by the different behavior of vortex rings in the initial region. Behavior of vortex rings in the initial region of pulsed jets was roughly classified into three types by Strouhal number, Sr0 (Sr0 ⟨ 0.9, 0.9 ≤ Sr0 ⟨ 2.6, Sr0 ≥ 2.6). It was found that the pulsation for Sr0 = 0.3 was the most dispersive wave in a jet column.
