Turbulence-airfoil interaction noise reduction using wavy leading edge: an experimental and numerical study

International audiencePassive treatments aiming at reducing turbofan broadband noise have been recently studied in the framework of European Project FLOCON. A concept based on a sinusoidal variation of the leading edge of a single airfoil expected to decrease interaction noise has been investigated by ONERA. Turbulence-airfoil interaction mechanism is achieved using a turbulence grid located upstream of a NACA airfoil tested in ISVR anechoic open wind tunnel. High noise reductions are obtained (3-4 dB) for all studied flow speeds. Experimental work is supplemented by numerical simulations using RANS/LES and CAA Euler-based approaches to predict the acoustic response of the wing. Isentropic turbulence is synthetically injected by means of a suited inflow boundary condition. Unsteady simulations are restricted to the baseline case (without treatment) and the present paper focuses on direct Euler methodology which provides reliable power spectrum density comparing to experiment. Effect of leading edge serrations on aerodynamics and noise is emphasized using Amiet thin airfoil theory, RANS solutions and available measurements

Numerical simulation of turbulence interaction noise applied to a serrated airfoil

International audienceTurbulent wakes generated by turbofan blades and interacting with the outlet guide vanes are known to be mainly contributing to broadband noise emission of aero-engines at approach conditions. Analytical approaches, such as the well-known Amiet model can be adopted to estimate the noise generated by turbulent flows impacting thin airfoils, but they are limited by the flat-plate assumptions. The development of numerical methods allowing more complex geometries and realistic flows is required. The method described in the present paper, is based on a CAA code solving the nonlinear Euler equations. The upstream turbulence is synthesized from a stochastic model and injected into the computational domain through an adapted boundary condition. It is first validated in 2D and 3D against academic flat plate configurations by comparison with Amiet solutions (exact in such cases). Then, 3D computations are applied to simulate the effect of a passive treatment (leading edge serrations) aiming at reducing turbulence interaction noise of an isolated airfoil studied in the framework of European project FLOCON. First calculations on baseline conditions are shown to be able to reproduce the measured spectra and far-field directivities, and the acoustic performances of the serrations (3-4 dB PWL reduction) are fairly well assessed too

Design aéroacoustique et prévision du bruit à large bande d'un étage de turboréacteur avec des aubes stator ondulées

International audienceThis work, realized in the framework of the European project TurboNoiseBB, presents the aeroacoustic design of serrated OGVs (Outlet Guide Vanes), including details on their broadband noise and aerodynamic performance. The serrated OGV corresponds to a modified stator from a turbofan model tested at the AneCom facility (Germany) and shared by the Consortium. Leading edge sinusoidal patterns with varying amplitude and wavelength along the span are designed in collaboration with Safran Aircraft Engines. Serrations are adjusted to account for the turbulence characteristics provided by RANS calculations. Optimal parameters are found using simple design rules discussed in the paper. Down selection of serrated OGV designs (patent pending) was performed in accordance with industrial specifications. Broadband noise simulations are performed using a CAA code solving the linearized Euler equations with a synthetic turbulence model. Numerical predictions at approach conditions are compared to available experimental measurements and an analytical Amiet-based model. Predictions on the untreated case show a fairly good agreement by comparison to the PSD measured at the bypass casing, and a PWL reduction around 3-4 dB roughly estimated by the design process is numerically achieved by the present method.Ces travaux, réalisés dans le cadre du projet européen TurboNoiseBB, présentent le design aéroaoustique d'aubes de redresseur avec serrations de bord d'attaque, incluant à la fois leur impact sur la génération du bruit à large bande et sur les performances aérodynamiques. Le stator à aubes ondulées est issu d'une maquette de soufflante de référence testée au banc AneCom et ouverte aux partenaires du Consortium. Le paramétrage des ondulations sinusoïdales à amplitude et longueur d'onde variables en envergure est réalisé en collaboration avec Safran Aircraft Engines. Les serrations sont ajustées en fonction des grandeurs charactéristiques de la turbulence fournies via des calculs RANS. Les paramètres optimaux sont obtenus à partir de lois semi-empiriques discutées dans le papier. La sélection finale des différents traitements (ayant conduit à un dépôt de brevet commun) est contrainte à des spécifications industrielles. Les prévisions de bruit à large bande sont obtenues à l'aide d'un code CAA résolvant les équations d'Euler linéarisées et couplé à un modèle de turbulence synthétique. Les simulations numériques en condition d'approche sont comparées aux mesures disponibles ainsi qu'à des solutions analytiques fondées sur le modèle d'Amiet. Les prévisions sur le cas de référence montrent un accord satisfaisant avec le spectre de pression aval mesuré au carter (dans le canal secondaire), et une réduction de puissance sonore de 3-4 dB grossièrement estimée à travers le design semi-empirique semble confortée par les premiers résultats numériques

Turbulence-airfoil interaction noise reduction using wavy leading edge: an experimental and numerical study

International audiencePassive treatments aiming at reducing turbofan broadband noise have been recently studied in the framework of European Project FLOCON. A concept based on a sinusoidal variation of the leading edge of a single airfoil aiming at reducing interaction noise has been investigated by ONERA. Turbulence-airfoil interaction mechanism is achieved using a turbulence grid located upstream of a NACA airfoil tested in ISVR anechoic open wind tunnel. High noise reductions are obtained (3-4 dB) for all studied flow speeds. Moreover, aerodynamic performances are shown to be slightly increased by the treatment that tends to reduce the drag without modify the mean loading. Experimental work is supplemented by numerical simulations using Large Eddy Simulations (LES) and direct Euler approaches to predict the acoustic response of the wing. LES is chained to a FWH (Ffowcs-Williams and Hawkings) integral to assess the radiated field. Isentropic turbulence is synthetically injected by means of a suited inflow boundary condition. Present computations are focused on the reference case (without treatment). Numerical predictions are compared to the experiment, and to analytical solutions issued from Amiet theory

ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction: Part II—Influence of the Acoustic Models

A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic solvers are compared. Some of the methods resort to the acoustic analogy, while some use a direct approach bypassing the calculation of a source term. Due to differing application objectives, the studied methods vary in terms of complexity to represent the turbulence, to calculate the acoustic response of the stator and to model the boundary and flow conditions for the generation and propagation of the acoustic waves. This diversity of approaches constitutes the unique quality of this work. The overall agreement of the predicted sound power spectra is satisfactory. While the comparison between the models show significant deviations at low frequency, the power levels vary within an interval of ±3 dB at mid and high frequencies. The trends predicted by increasing the rotor speed are similar for almost all models. However, most predicted levels are some decibels lower than the experimental results. This comparison is not completely fair—particularly at low frequency—because of the presence of noise sources in the experimental results, which were not considered in the simulations

Future Aircraft and the Future of Aircraft Noise

In order to cope with increasing air traffic and the requirement to decrease the overall footprint of the aviation sector - making it more sustainably and acceptable for the whole society - drastic technology improvements are required beside all other measures. This includes also the development of novel aircraft configurations and associated technologies which are anticipated to bring significant improvements for fuel burn, gaseous and noise emissions compared to the current state and the current evolutionary development. Several research projects all over the world have been investigating specific technologies to address these goals individually, or novel - sometimes also called "disruptive" - aircraft concepts as a whole. The chapter provides a small glimpse on these activities - mainly from a point of view of recent European funded research activities like Horizon2020 projects ARTEM, PARSIFAL, and SENECA being by no-way complete or exhaustive. The focus of this collection is on noise implications of exemplary novel concepts as this is one of the most complicated and least addressed topics in the assessment of aircraft configurations in an early design stage. Beside the boundary layer ingestion concept, the design process for a blended wing body aircraft is described, a box-wing concept is presented and an outlook on emerging supersonic air transport is given

Turbulence-airfoil interaction noise reduction using wavy leading edge: an experimental and numerical study

International audiencePassive treatments aiming at reducing turbofan broadband noise have been recently studied in the framework of European Project FLOCON. A concept based on a sinusoidal variation of the leading edge of a single airfoil expected to decrease interaction noise has been investigated by ONERA. Turbulence-airfoil interaction mechanism is achieved using a turbulence grid located upstream of a NACA airfoil tested in ISVR anechoic open wind tunnel. High noise reductions are obtained (3-4 dB) for all studied flow speeds. Experimental work is supplemented by numerical simulations using RANS/LES and CAA Euler-based approaches to predict the acoustic response of the wing. Isentropic turbulence is synthetically injected by means of a suited inflow boundary condition. Unsteady simulations are restricted to the baseline case (without treatment) and the present paper focuses on direct Euler methodology which provides reliable power spectrum density comparing to experiment. Effect of leading edge serrations on aerodynamics and noise is emphasized using Amiet thin airfoil theory, RANS solutions and available measurements

Acoustic transmission through a 3D rotating fan using Computational AeroAcoustics

International audienc

Numerical simulation of turbulence interaction noise applied to a serrated airfoil

International audienceTurbulent wakes generated by turbofan blades and interacting with the outlet guide vanes are known to be mainly contributing to broadband noise emission of aero-engines at approach conditions. Analytical approaches, such as the well-known Amiet model can be adopted to estimate the noise generated by turbulent flows impacting thin airfoils, but they are limited by the flat-plate assumptions. The development of numerical methods allowing more complex geometries and realistic flows is required. The method described in the present paper, is based on a CAA code solving the nonlinear Euler equations. The upstream turbulence is synthesized from a stochastic model and injected into the computational domain through an adapted boundary condition. It is first validated in 2D and 3D against academic flat plate configurations by comparison with Amiet solutions (exact in such cases). Then, 3D computations are applied to simulate the effect of a passive treatment (leading edge serrations) aiming at reducing turbulence interaction noise of an isolated airfoil studied in the framework of European project FLOCON. First calculations on baseline conditions are shown to be able to reproduce the measured spectra and far-field directivities, and the acoustic performances of the serrations (3-4 dB PWL reduction) are fairly well assessed too