Experimental velocity measurements of a low-speed jet, performed using time-resolved
tomographic PIV, are used to study the dynamics of large-scale structures and their sound
radiation. The experimental results show the roll-up of axisymmetric vortices that pair
downstream, and subsequently lose their azimuthal coherence. Models of linear instability
waves using both steady laminar and mean-field base flows flow are applied. While good
agreement can be obtained for the vortex roll-up frequency in the near-nozzle region using
the laminar base flow, non-linear effects must be included, via the mean field, in order
to capture the downstream evolution of both the fundamental and subharmonic (vortex
pairing). The velocity fluctuations for both frequencies have a wave-packet structure with
some 极tter in the form of modulations of the spatial extent and amplitude of the envelope.
The sound radiation is modelled using a 极ttering wave-packet model, an shows agreement
with the exponential directivity shape of Laufer and Yen (J. Fluid Mech. 134, 1983). 自适应粒子成像测速场仪（PIV） 德国LaVision PIV/PLIF粒子成像测速场仪 时间分辨粒子成像测速系统(TR-PIV) 体视层析粒子成像测速系统(Tomo-PIV) 三维立体PIV
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