Modeling of coherent structures in a turbulent jet as global linear instability wavepackets: Theory and experiment

Perturbation wavepackets in a jet, induced by externally applied forcing, are computed from the linearized equations of motion. An experimentally measured mean flow serves as the base state for this linear analysis, and optimally amplified mono-frequency perturbations are identified, in the sense of maximal gain between the forcing energy input and the flow response energy. Sub-optimal orthogonal forcing/response structures are also discussed. Linear analysis results are then compared to measured perturbation wavepackets in the jet experiment. The study addresses the question to what extent the true dynamics of a turbulent jet can be represented by a model based on linear instability.