Interaction between wavepackets and streaks in turbulent jets

We propose a formulation to study the effect of streaks in the spatial development of wavepackets. To this end, a modified version of the parabolised stability equations (PSE) linearized around a streak-containing mean flow is used, which considers a series of azimuthal wavenumbers in the solution. In the present case, streaks are obtained from experiments using spectral proper orthogonal decomposition applied to particle image velocimetry data, and extrapolated in the radial direction using a Gaussian fit. Streaks and rolls predicted by resolvent analysis are also used in the analysis to evaluate the effect of streamwise vortices in the development of the noise-generating structures. Results show that streaks non-trivially modify the spatial support of the Kelvin-Helmholtz wavepackets and their phase velocity, which may lead to changes in the sound generation efficiency of the jet. New structures across the shear layer induced by the presence of streaks are also observed further downstream for high streak amplitudes.