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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...

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...

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.

Hybrid CFD/CAA methods have generally to be used for the numerical simulation of trailing-edge noise (see [9, 20] for instance). This study focuses on the first step of such hybrid methods, which is to predict the unsteady aerodynamic sources by the mean of a 3D unsteady simulation of the flow. Such a simulation is however generally still away from the numerical capabilities of ‘usual’ supercomputers. This paper investigates the use of a zonal LES method (based on the NLDE – Non-Linear Disturbance Equations – technique) for the numerical prediction of the aerodynamic noise sources. This method makes it possible to perform only zonal LES close to the main elements responsible of sound generation, while the overall configuration is only treated by a RANS approach. Attention will be paid to the specific boundary treatment at the interface between the RANS and LES regions. More precisely, the problem of the generation of turbulent inflow conditions for the LES region will be carefully addressed. The method is first assessed in the simulation of a flat plate ended by a blunted trailing-edge, and then applied to the simulation of the flow over a NACA0012 airfoil with blunted trailing-edge.

A source-to-far-field computation procedure aimed at predicting the noise generated by rotor-stator fan interactions is presented here. Interaction noise sources are assessed using a three-dimensional Reynolds-averaged Navier-Stokes (RANS) code. A modal expansion is applied to the computational fluid dynamics (CFD) data, and a source model is used to link the CFD to an Euler code simulating the acoustic propagation. Far-field noise is classically obtained by means of a Kirchhoff integral. The source model is detailed and validated over a selected benchmark. Then the hybrid method is applied to a turbofan model, tested in the German-Dutch Wind Tunnel. Simulations are compared to boundary element method computations previously performed and used here to validate the no-flow solution. Interacting cut-on mode amplitude deduced from CFD output postprocessing is adjusted to fit in-duct measurements on the outer wall. The predicted radiation field is related to the directivity patterns measured at several axial positions upstream of the fan inlet and fairly good agreement is found using the RANS/Euler/Kirchhoff procedure.

This study presents a highly-resolved Large Eddy Simulation of a three-element highlift airfoil with deployed slat and flap, which involves a large amount of CPU resources (2.6 billions of grid cells and 6 millions of CPU hours). The aim of this simulation is double: the first objective is to perform a detailed flow analysis and identify the physical events responsible for noise generation as well as the implied flow mechanisms; the second objective is to provide an important numerical database that may be used in the future to assess more affordable numerical approaches based for instance on hybrid RANS/LES methods. The assessment of the present LES relies on a recent experimental campaign performed in Onera F2 wind tunnel in the framework of a joint Onera/DLR project named LEISA2.

This study deals with the numerical investigation of the flow around a high-lift airfoil with deployed slat and flap, with focus being made on the slat cove region. Two different techniques are used and compared to simulate the unsteady flow around such an airfoil, both being based on a hybrid RANS/LES formulation in order to minimize as much as possible the computational resources. In this paper, a comparison of the results from these two approaches (namely ZDES and NLDE) is presented, both from the statistical and unsteady points of view. The two approaches provide results which are in excellent respective agreement.

This study presents numerical simulations of the unsteady flow and noise generation phenomena in the slat cove of a highlift wing profile by mean of a zonal hybrid RANS/LES approach. These computations are part of a joint numerical/experimental aeroacoustics collaborative program, dedicated to slat flow analysis. For that purpose, a dedicated twoelement wing profile (slat+main body) has been designed in order to isolate the slat noise sources from other possible spurious sources (flap for instance), while minimizing mean flow deflection effects in order to improve the reliability of open-jet wind tunnel measurements. The design of this two-element airfoil has been done numerically using an optimization process based on steady RANS calculations. This airfoil has been investigated experimentally in Ecole Centrale de Lyon open jet facility, therefore providing unsteady wall-pressure measurements in the slat cove area and farfield acoustic measurements. Unsteady zonal hybrid RANS/LES simulations have been performed to provide a comprehensive description of the unsteady flow inside the slat cove, with focus being made on the noise generation processes. A fine physical unsteady analysis of the flow inside the slat cove is presented, as well as a comparison of numerical results with available experimental ones. The pressure spectra associated to the slat cove flow appear to be characterized by several tonal peaks emerging from a global broadband content. The existence of such peaks is discussed and attributed to a feedback loop involving the main shear layer inside the slat cove. A theoretical law is proposed and assessed at the end of the paper to predict the associated tonal frequencies.