Dynamic behaviour of wave packets in turbulent jets

The present study proposes a data-driven strategy to extract the dynamics of wave-packets from low-speed velocity field measurements. The flow field under study is a subsonic turbulent round jet at Re = 33000, measured over a 20-nozzle-diameters domain in the axial direction using low-repetition-rate planar Particle Image Velocimetry. The turbulent features in the jet have been extracted by Proper Orthogonal Decomposition of the jet velocity field over the whole extension of the domain. The modes produced describe the evolution of the turbulent features in the axial and radial directions of the jet. The temporal evolution of turbulent flow structures and the associated pressure fluctuations, which are not directly accessible from the low-speed measurements, have been estimated using an advection-based Galerkin projection model. The extracted velocity/pressure modes describe a set of modulated waves in the axial direction, which shares many similarities with wave-packets already observed in literature. This behaviour suggests that the employed strategy is effective in retrieving the dynamics of wave-packets extending over the entire measurement domain, paving the way to the estimation of their sound emission from low-speed measurements.