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 極tter in the form of modulations of the spatial extent and amplitude of the envelope. The sound radiation is modelled using a 極ttering wave-packet model, an shows agreement with the exponential directivity shape of Laufer and Yen (J. Fluid Mech. 134, 1983). 自適應(yīng)粒子成像測(cè)速場(chǎng)儀（PIV） 德國(guó)LaVision PIV/PLIF粒子成像測(cè)速場(chǎng)儀 時(shí)間分辨粒子成像測(cè)速系統(tǒng)(TR-PIV) 體視層析粒子成像測(cè)速系統(tǒng)(Tomo-PIV) 三維立體PIV