Flowfield and acoustic properties of a Mach number 0.9 jet at a low Reynolds number

Downstream subsonic jet noise: link with vortical structures intruding into the jet core

“…2(b). They are in very good agreement for all observation angles with experimental data from jets with similar Mach numbers but various Reynolds numbers [9,11,12]. As expected, the acoustic levels reach a peak for an angle about θ = 30 • .…”

“…It is dominated by low frequency components, with a peak around a Strouhal number St = 0.2. This spectrum has been observed experimentally for low observation angles, as illustrated by measurements of Stromberg et al [9] on a M = 0.9, Re D = 3.6 × 10 3 jet, and those of Long and Arndt [10] on a M = 0.52, Re D = 8.5 × 10 4 jet. The classical interpretation is that for low angles, jet noise is mainly associated to the large-scale turbulent structures, and is insensitive to variations in the Reynolds number.…”

“…2(b). Ils sont en très bon accord avec les niveaux mesurés sur des jets au même nombre de Mach et avec des nombres de Reynolds variés [9,11,12]. La dispersion des niveaux pour des angles supérieurs à 60 • est attribuée à un effet du nombre de Reynolds, car la contribution des sources de bruit liées à la turbulence fine n'est plus négligeable dans cette zone.…”

“…2(a) le spectre obtenu pour un angle de 30 • par rapport à la direction de l'écoulement. Celui-ci est dominé par les fréquences voisines d'un nombre de Strouhal de St = 0,2, conformément aux spectres mesurés pour des petits angles d'observation [9,10]. On interprète classiquement ce type de spectre en associant le rayonnement aval des jets aux grandes structures de l'écoulement.…”

Nonlinear interaction model of subsonic jet noise

“…Laufer & Yen (1983) located the source of sound with the nonlinear saturation of instability waves and noted that, while the near-field pressure varied linearly with disturbance amplitude, the acoustic far field had a quadratic dependence. Stromberg et al (1980) made experiments in jet Mach number MZ0.9 and ReZ3600 based on jet diameter and also suggested that their data supported a nonlinear mechanism of noise generation. This experiment is attractive for analysis and simulation, not least because the authors included velocity profiles from the region near the nozzle exit.…”