Numerical and experimental characterization of fan noise installation effects.

International audienceWithin the context of the two major European Research Projects, NACRE and OPENAIR, the potential of acoustic installation effects on the aft fan noise radiated by innovative installations of coaxial turbofans are evaluated. Three different installation concepts are considered: a semi-buried engine, a rear-fuselage nacelle and, finally, a scarfed nozzle. The main objective of these concepts is to reduce the acoustic radiation of fan noise through the engine nozzle towards the ground, without significant losses in the aerodynamic performance. This evaluation relies on numerical simulations achieved with Onera’s solvers, namely sAbrinA-V0 (CAA) and BEMUSE (BEM).The nozzle configurations are typical of coaxial turbofans with a large bypass ratio, including 3D effects from the internal bifurcation and, possibly, the external pylon or fuselage. To obtain a representative fan noise effect, several levels of complexity are used to numerically model the fan noise sources. The most advanced acoustic computations rely on Random Phase Multi-modal Injection (RPMI), an innovative technique based on the optimization of the modal phases, in order to obtain, with a minimum number of CAA computations, the contribution of all cut-on modes with evenly distributed acoustic power, summed in an un-correlated way. Noise propagation also accounts for the refraction effects, due to the large velocity gradients in the coaxial flow. For this purpose, non-homogeneous RANS mean flows were computed by Onera, AIRBUS and SNECMA respectively, for the reference (isolated) and the installed configurations, allowing their respective aerodynamic performances to be checked. For all three configurations, the installation effect is evaluated as a combination of the result of the CAA computation in the near-field and an extrapolation in the far-field, using the BEM or Kirchhoff integral methods to take into account the acoustic scattering on different fuselage parts. Undeniable benefits in noise reduction by the use of such installations are demonstrated. However, additional studies are still required to confirm these benefits, especially by improving the modeling of the fan noise sources and optimizing the acoustic shielding process

ÉTALONNAGE D'UN RÉSEAU DE MICROPHONES

Les réseaux de microphones pariétaux permettent d'aborder la mesure de la région des petits nombres d'onde du spectre des fluctuations de pression sous une couche limite turbulente. Un réseau de microphones constitue un filtre en nombre d'onde dont l'efficacité dépend de la précision de l'étalonnage relatif des microphones. On propose une méthode permettant un étalonnage en module et en phase sur une large bande de fréquence. De plus, les microphones sont tous étalonnés simultanément sur leur support d'essai.Wall-pressure microphone arrays are commonly used to measure the low wave number components of the wall pressure fluctuations spectrum beneath a turbulent boundary layer. A microphone array acts as a wavenumber filter. Its efficiency depends upon the accuracy with which the relative sensitivity of microphones are determined. A method is proposed, which allows a phase and level calibration over a large frequency band. Moreover, all microphones are simultaneously calibrated on their test mount

On LAGOON Nose Landing Gear CFD/CAA Computation over Unstructured Mesh using a ZDES approach

This paper is part of ONERA's effort to compute the noise generation around landing gears, effort that has been shown with studies on a variety of configurations such as the ones included inside the BANC-II (Benchmark problems for Airframe Noise Computations). In this case, the addressed geometry is the LAGOON baseline nose landing gear. On the present computation, a refined unstructured mesh is generated for resolving the boundary layer up to y+ around one. The simulation of the flow was performed using a Zonal Detached Eddy Simulation (ZDES) model, implemented inside ONERA's code CEDRE. The transient data obtained were used as input for a Ffowcs-Williams and Hawkings computation over the skin of the landing gear and on a porous surface around it, which was performed using ONERA's in-house code KIM. Both the aerodynamic and aeroacoustic results are compared with the experimental ones obtained at F2 and CEPRA19 test campaigns. The comparisons obtained show a good agreement in terms of mean field, wall pressure (mean and spectral content) and aeroacoustic far-field measurements

Lattice-Boltzmann Flow Simulation of a Two-Wheel Landing Gear

International audienceThis paper presents numerical flow predictions of a two-wheel landing gear. Computations are based on the Lattice Boltzmann Method implemented in LaBS, a solver developed by a French consortium led by industrial companies and academic institutes. The landing gear geometry is one of the LEG (“Landing gear noise Evaluation Geometry ”) landing gear model configurations designed and tested by JAXA. This model includes geometric details such as the wheel-caps with cooling holes, brake calipers, and torque link. The unsteady flow simulations are achieved on “octree” Cartesian grids using cubic cells with refinement doubled along surfaces assigned by the user. Solid surfaces are treated via an Immersed Boundary Method. Two computations are currently achieved on grids with coarse and medium resolutions, and a final computation on a fine grid is still running. The time-averaged wall pressure on the wheels and velocity components in the landing gear wake show a global agreement with the steady pressure taps and PIV respectively. The main discrepancies appears in the flow deviation because the boundary conditions of the flowdiffers from open-jet condition in CFD to closed-test section in wind-tunnel. The medium grid compuations globally improves the time-averaged and unsteady aerodynamic predictions regarding the coarse grid results. Given their accuracy, these results already confirms the relevancy of the lattice-Boltzmann method for the landing-gear flow simulation.Cet article présente les prévisions numériques du bruit d'un train d'atterrissage à deux roues.Les calculs sont basés sur la méthode Lattice Boltzmann implémentée dans LaBS, un solveur développé par un consortium français dirigé par des entreprises industrielles et des instituts universitaires. La géométrie du train d'atterrissage LEG est un modèle de train d'atterrissage conçu et testé par la JAXA. Ce modèle comprend des détails géométriques tels que les jantes des roue avec des trous de refroidissement, des éléments de freinage et un compas. Les simulations d'écoulement instationnaire sont réalisées sur des grilles cartésiennes dites "octree" utilisant des cellules cubiques avec un raffinement doublé le long des surfaces assignées par l'utilisateur. Les surfaces solides sont traitées par une méthode des frontières immergées. Deux calculs sont actuellement effectués sur des résolutions grossières et moyennes, et un calcul final sur une grille fine est toujours en cours. La pression moyenne sur les roues et les composantes de vitesse dans le sillage du train d'atterrissage montrent un accord global avec les mesures réalisées en soufflerie. Ces résultats, bien que limité à un maillage de taille moyenne, confirme l'intérêt de la méthode LBM pour la simulation d'écoulement de train d'atterrissage

LES of trailing edge flow with application to radiated noise

Communication to : 1st AFOR international conference on DNS and LES, Ruston (USA), August 4-8, 1997Available from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1997 n.120 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Simulation de la propagation acoustique au sein d'un ecoulement aerodynamique par resolution des equations d'Euler

Communication to : Premieres journees de Troussencourt sur l'Acoustique de Galbrun, Troussencourt (France), 07-09 avril 1999Available from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1999 n.78 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Numerical simulation of propagation of small perturbations interacting with flows and solid bodies

Communication to : 7th AIAA/CEAS aeroacoustics conference, Maastricht (Pays-Bas), May 28-29, 2001SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.2001 n.102 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc