Inﬂuence of nozzle-exit boundary-layer proﬁle on high-subsonic jets Christophe Bogey * and Olivier Marsden † Laboratoire de M´ecanique des Fluides et d’Acoustique UMR CNRS 5509, Ecole Centrale de Lyon 69134 Ecully, France The inﬂuence of the nozzle-exit boundary-layer proﬁle on high-subsonic round jets is investigated by performing compressible large-eddy simulations of four jets using low- dissipation numerical schemes. The jets are isothermal, and have a Mach number of 0.9 and a diameter-based Reynolds number of 5 × 10 4 . They originate from a pipe nozzle in which a trip-like forcing is applied. In that way, they exhibit, at the exit section, around 6% of peak turbulence intensity and boundary-layer velocity proﬁles characterized by a momen- tum thickness of about 2.8% of the nozzle radius, yielding a Reynolds number around 700, and by shape factors equal to 1.68, 1.77, 2.01 and 2.36. The results from the fourth case with a laminar velocity proﬁle diﬀer signiﬁcantly from those from the three ﬁrst cases with transitional proﬁles, whose accuracy is shown by a grid reﬁnement study. Clear trends are thus identiﬁed when the shape of the exit boundary-layer proﬁle changes from laminar to turbulent. Higher azimuthal modes and higher Strouhal numbers are found to predom- inate, respectively, at the pipe exit close to the wall and early on in the mixing layers. The latter appear to develop more slowly, leading to a longer potential core, and weaker velocity ﬂuctuations are obtained in the shear layers and on the jet axis. Finally, lower noise levels are generated in the acoustic ﬁeld. I. Introduction There has been a considerable amount of work on the eﬀects of jet initial conditions for more than four decades. In particular, a great attention has been paid to the state of the nozzle-exit boundary layer, which may vary from one experiment to another depending on the facility characteristics and on the nozzle diameter and geometry. For instance, the jets are often initially laminar in small-scale experiments, whereas they are initially turbulent in full-scale experiments. In order to make meaningful comparisons, it is thus necessary in the ﬁrst case to trip the boundary layer in the nozzle to generate turbulent exit conditions, as was the case in the pioneering work of Crow & Champagne. 1 The diﬀerences obtained between initially laminar and initially turbulent jets have been described in a number of papers. It has been shown by Hill et al., 2 Browand & Latigo, 3 Hussain & Zedan 4 and Husain & Hussain, 5 among others, that downstream of the nozzle lip, the turbulence intensity rapidly increases and reaches a peak in the laminar case, whereas it grows monotonically in the turbulent case. Moreover, the jet ﬂow development is found to be faster in the former case than in the latter, leading to a shorter potential core and a higher rate of centerline velocity decay, refer to the data of Hill et al., 2 Raman et al., 6, 7 Russ & Strykowski 8 and Xu & Antonia, 9 for example. The impact of the nozzle-exit boundary-layer state is also signiﬁcant on jet acoustic sources, as pointed out in the review papers by Crighton 10 and Lilley. 11 It has notably been established that initially laminar jets emit more noise than initially turbulent jets, eg in Maestrello & McDaid, 12 Zaman 13, 14 and Bridges & Hussain, 15 and that the additional noise can be attributed to the pairings of coherent vortices in the shear layers. * CNRS Research Scientist, AIAA Senior Member & Associate Fellow, christophe.bogey@ec-lyon.fr † Assistant Professor at Ecole Centrale de Lyon, olivier.marsden@ec-lyon.fr 1 of 18 American Institute of Aeronautics and Astronautics Downloaded by Christophe Bailly on August 26, 2014 | http://arc.aiaa.org | DOI: 10.2514/6.2014-2600 20th AIAA/CEAS Aeroacoustics Conference 16-20 June 2014, Atlanta, GA AIAA 2014-2600 Copyright © 2014 by Christophe Bogey. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. AIAA Aviation