On the spectra of nozzle-exit velocity disturbances in initially nominally turbulent, transitional jets

In a recent paper by C. Bogey, O. Marsden, and C. Bailly ["Large-eddy simulation of the flow and acoustic fields of a Reynolds number 10 5 subsonic jet with tripped exit boundary layers," Phys. Fluids 23 (3), 035104 (2011)], simulation results were presented for round jets with tripped boundary layers, displaying nozzle-exit conditions typical of initially nominally turbulent, transitional jets, namely laminar mean velocity profiles and high fluctuation intensities. The velocity spectra evaluated just downstream of the nozzle exit are re-examined here with respect to literature data. They agree qualitatively very well with spectra obtained in a fully turbulent pipe flow using direct numerical simulation. The wave numbers dominating in the azimuthal direction are also consistent with measurements of spanwise energy distribution in fully turbulent boundary layers. The initial turbulent structures in the jets, therefore, appear to be organized similarly to those in fully developed wall-bounded flows.