Effect of a flight stream on subsonic turbulent jets

We study a turbulent jet in a uniform external flow stream. This flow configuration is of interest in aeroacoustics and aeronautics, as it mimics the effect of forward flight in real aircraft. We perform a thorough characterization of the effect of the flight stream, combining experimental and numerical data, signal processing, and linear modeling. We show that the flight stream reduces fluctuation energy in a broad region of the frequency-wavenumber space and stabilizes flow structures underpinned by modal and non-modal instability mechanisms. Streaky structures, associated with helical azimuthal wavenumbers and very slow timescales, are the most strongly affected by the flight stream.