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This study deals with the development of a numerical wire mesh screen model for the unsteady simulation of aeroacoustic configurations. Such devices are indeed of growing interest for practical app...

International audience; The scattering of an acoustic wave by a 3D spatially-developing plane turbulent mixing layer is investigated by means of a Large Eddy Simulation (LES). First, a plane turbulent mixing layer of initial Reynolds number Reω, 0 ≈ 1200 and convective Mach number Mc ≈ 0.12 is computed and its characteristics are validated by comparisons to experimental and numerical studies. Then, an acoustic source is introduced in the computational domain and the LES of both the turbulent mixing layer and the acoustic field is carried out, allowing the direct computation of the scattered pressure field. Computational Aero Acoustics (CAA) methods have been implemented to minimize spurious pressure fluctuations created while the turbulent structures leave the computational domain. The side-lobes of the scattered pressure power spectral density are recovered and a parametric study, involving the convection velocity of the large turbulent structures, the amplitude and the tonal frequency of the source is carried out. The part of scattered energy, the frequency shift of the side-lobes and the spectra decrease are found to be correctly estimated. Analysis of directivity at the side-lobes frequencies show a progressive re-distribution of the acoustic energy, as the acoustic wave propagates through the turbulent shear layer.

This study presents hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations of the unsteady flow and noise-generation phenomena in the slat cove of a high-lift wing profile. These computations are part of a joint numerical/experimental aeroacoustics collaborative program dedicated to slat-flow analysis. A dedicated two-element wing profile (slat plus main body) has been designed to isolate slat noise from other possible sources (e.g., the flap), while minimizing mean flow deflection effects, to improve the fidelity of open-jet wind-tunnel measurements. The design of this two-element airfoil has been performed numerically, using an optimization process based on steady Reynolds-averaged Navier–Stokes calculations. This airfoil has been investigated experimentally at the Ecole Centrale de Lyon open jet facility. Unsteady zonal hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations have been performed to provide a comprehensive description of the unsteady flow inside the slat cove, focusing on th...

A methodology to mix Chimera and Immersed Boundary approaches in the same CFD computation is presented in order to deal with complex geometries. Where accuracy is required in a vicinity of an obstacle, a body-fitted mesh is used to accurately simulate the boundary layer. Otherwise, an immersed boundary method (IBM) is applied to deal with this obstacle. Each body-fitted mesh is generated independently in an overset grid fashion. A set of Cartesian grids that are adapted to the spatial resolution of body-fitted grids and immersed boundaries is generated automatically and overlaps the body-fitted grids. In this paper, we describe the overall procedure to mix the overset grid and immersed boundary approaches, then we detail how the present IBM enables to deal with geometrically complex configurations. Finally, preliminary results of the simulation of a turbulent flow past two cylinders in tandem are presented.

This study presents several unsteady computations of the 30P30N three-element high-lift airfoil, focused on slat noise prediction. These simulations rely on several RANS/LES approaches: two global hybrid approaches, DDES (Delayed Detached Eddy Simulation) and ZDES (Zonal Detached Eddy Simulation) and one zonal approach, the NLDE (Non-Linear Disturbance Equations). Global approaches compute all the geometry, while zonal simulations only consider an LES domain clustered around the slat to save computational resources. Two grid resolutions are considered, in order to perform a critical comparison of both the modeling and grid resolution effects for this kind of configuration. The obtained results are favorably compared to near-field results measurements obtained in JAXA low-speed Wind Tunnel (JAXA-LWT2): narrow band peaks present in the pressure spectra are well recovered by all the simulations, with a very good agreement with the measurements for the fine grid results, while the medium grid simulations tend to over-estimate the magnitude of these peaks. It is also observed that the DDES approach seems to delay the development of instabilities in the slat cusp shear layer, while other approaches lead to a faster break-up of the shear layer. The zonal NLDE approach leads to significant CPU time savings due to the reduced number of grid points, as well as to shorter transient times. However, such simulations do not account for the whole diffraction and reflection effects, as observed on the far-field acoustic field.

The scattering of an acoustic wave by a fully turbulent mixing layer is investigated by means of a Large Eddy Simulation. The turbulent characteristics of the mixing layer have been validated by comparison to experimental and numerical studies. Computational Aero Acoustics (CAA) methods have been used to minimize spurious pression fluctuations created while the turbulent structures leave the computational domain. Then, an acoustic source has been placed inside a uniform flow and the acoustic propagation has been validated. Finally, both the turbulent mixing layer and the acoustic field are calculated and the scattering phenomenon is investigated. The ’double-humped’ structures of the far field power spectral density is recovered and a parametrical study, involving the tonal frequency of the source is carried out. The comparison to previous experimental works have been enabled thanks to the definition of a relevant scattering parameter. The spectra are in good agreement with experimental works on acoustic scattering. The frequency shift of the sidelobes and the spectra’s decrease are well predicted and in a good agreement with the ones found in the literature.