Investigation of downstream and sideline subsonic jet noise using Large Eddy Simulation

Abstract

The sound fields radiated by Mach number 0.6 and 0.9, circular jets with Reynolds numbers varying from 1.7 × 10 3 to 4 × 10 5 are investigated using Large Eddy Simulations. As the Reynolds number decreases, the properties of the sound radiation do not change significantly in the downstream direction, whereas they are modified in the sideline direction. At low Reynolds numbers, for large angles downstream from the jet axis, the acoustic levels are indeed remarkably lower and a large high-frequency part of the sound spectra vanishes. For all Reynolds numbers, the downstream and the sideline sound spectra both appear to scale in frequency with the Strouhal number. However their peak amplitudes vary following two different velocity exponents according to the radiation direction. The present observations suggest the presence of two sound sources: a Reynolds number-dependent source, predominant for large radiation angles, connected to the randomlydeveloping turbulence, and a deterministic source, radiating downstream, related to a mechanism intrinsic to the jet geometry, which is still to be comprehensively described. This view agrees well with the experimental results displaying two distinguishable components in turbulent mixing noise [1,2]. Keywords

Direct Noise Computation of the Turbulent Flow Around a Zero-Incidence Airfoil

“…Both explicit schemes such as Tam and Webb's [1] dispersion-relation-preserving scheme or those proposed by Bogey and Bailly [2] and implicit schemes such as Padé-type schemes [3,4] have been successfully applied to aeroacoustic simulations at high Reynolds numbers. The field of jet aeroacoustics has been particularly active in the advancement of these techniques, and a number of high-Reynolds-number jet flow simulations can be found in the literature [5][6][7][8].…”

“…They found a reasonable agreement between their computed acoustic field and Blake's [18] experimental results for high frequencies, but lowfrequency values were badly estimated, due to the insufficient transversal extent of their computational domain. Manoha et al [10] performed an LES simulation around a NACA 0012 airfoil at a chord-based Reynolds number of Re c 2:86 10 6 , placed at 5 deg of incidence to the incoming flow. A Kirchhoff formulation was used to calculate the acoustic far field.…”

Investigation of a High-Mach-Number Overexpanded Jet Using Large-Eddy Simulation

“…In high-Reynolds-number subsonic jets, two noise components have been identified [12][13][14][15]. One dominates in the downstream direction with a noise source located around the end of the potential core [16,17], and another dominates in the sideline direction and is probably linked to the turbulent mixing in the shear layer [13,17].…”

“…Such simulations have, for instance, been performed by Bogey et al [15,36,37] in order to study the influence of the Reynolds number and of the initial conditions in subsonic jets, by Viswanathan et al [38] and Liu et al [39] to improve the prediction of broadband shock-associated noise and screech tone for real nozzle geometries, and by Berland et al [22] to investigate screech tone generation in a plane supersonic jet. In these works, the use of low-dissipation and low-dispersion numerical schemes is usually recommended [40][41][42] to ensure numerical accuracy.…”

Direct Noise Computation of a Shocked and Heated Jet at a Mach Number of 3.30

“…[11][12][13][14] One is dominating in the downstream direction with a noise source located around the end of the potential core, 15,16 and another is dominating in the sideline direction and is probably linked with the turbulent mixing in the shear layer.…”