Analysis of noise radiation mechanisms in hot subsonic jet from a validated large eddy simulation solution

Abstract

In the framework of jet noise computation, a numerical simulation of a subsonic turbulent hot jet is performed using large-eddy simulation. A geometrical tripping is used in order to trigger the turbulence at the nozzle exit. In a first part, the validity of the simulation is assessed by comparison with experimental measurements. The mean and rms velocity fields show good agreement, so do the azimuthal composition of the near pressure field and the far field spectra. Discrepancies remain close to the nozzle exit which lead to a limited overestimation of the pressure levels in both near and far fields, especially near the 90∘ angular sector. Two point correlation analyses are then applied to the data obtained from the simulation. These enable to link the downstream acoustic radiation, which is the main direction of radiation, to pressure waves developing in the shear layer and propagating toward the potential core end. The intermittency of the downstream acoustic radiation is evidenced and related to the coherent structures developing in the shear layer.

Turbulent jet simulation using high-order DG methods for aeroacoustic analysis

“…(a) φ 50 nozzle geometry (b) global view of the mesh The meshing methodology employed here is described in [15,25] for the jet noise simulation. This methodology consists in having a fine resolution of the mesh near the nozzle exit.…”

“…To date, a number of strategies have been developed to obtain a turbulent flow at nozzle exit. They consist in adding disturbances in the boundary layer inside the nozzle which are either divergence-free "vortex-ring" [7,8,9,10], perturbations based on annular mixing layer linear stability theory [11,12] or a geometrical tripping [13,14,15], in order to force the transition towards a turbulent state. Nonetheless a fine mesh resolution is needed to convect the turbulent fluctuations.…”

Large-Eddy Simulation and Far Field Acoustics of a Subsonic Hot Jet

“…The grid is stretched from a refined zone, in which the flow is accurately calculated, to the simulated domain boundaries in order to damp acoustic waves before they reach the borders and thus avoid spurious reflections. The details of mesh refinement can be found in the respective papers [10] [22]. The main characteristics of both grids are summarized in Table 2.…”

“…The first one called 'Fine' is issued from Huet [10] and consists in 30x10 6 cells, while the second one called 'Very Fine' contains 240 x10 cells and was provided by Lorteau et al [22]. The grid of both meshes is axi-symmetrical and structured and includes a O-type treatment on the jet axis to ensure that hexahedral cells have an homogeneous size in the core region.…”

“…Previously, Lorteau et al [22] performed an analysis of the near field pressure from an experimental database of an isothermal and a hot subsonic jet. They established the existence of a sector linked to an acoustic behaviour in the near field in which the low frequencies around St = 0.2 and the axisymmetric mode are dominant.…”