Qualitative dynamics of wavepackets in turbulent jets

Abstract

It has long been established that turbulent jets comprise large-scale coherent structures, now more commonly referred to as "wavepackets". These structures exhibit a remarkable spatio-temporal organisation, despite turbulence. In this work we analyse, from a qualitative point of view, the temporal dynamics of axisymmetric wavepackets educed, experimentally, from subsonic iso-thermal jets. We use the data presented by, where time-series of the wavepackets are extracted at different streamwise locations. A thorough analysis is performed, statistical tools are used for estimating the embedding and correlation dimensions characterising the dynamical system. System identification is used for computing nonlinear surrogate models. Finally, control-oriented linear models are computed. The goal of the contribution is to assess the extent to which non-linear models are necessary, or appropriate, for description of the temporal wave-packet dynamics and to provide a complementary perspective to the current modelling.