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An exhaustive analytical predictive tool of the aerodynamic noise generated by deflected high-lift devices is presented in this paper. Three-dimensional effects are especially investigated. An analytical model of flap side edge noise is first proposed, on the basis of existing literature. Secondly, another model is proposed to simulate slat horn no...
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... for different oncoming flow velocities (60, 80 m/s) and different geometrical angles of attack αg defined with respect to the incident mean flow (15 • , 17.5 • and 20 • ). Note that, due to the open jet deflection by the wing, the effective angle of attack for the same load in free air would be substantially smaller. Typical spectra are shown in Fig. 10 and 11 for the real three-dimensional configuration and a two-dimensional configuration with a constant cross-section slat deflected over the whole span (no gap). A correction has been applied to account for the different span length in both configura- tions, in order to extract the contribution of the 3D source. Apart from a small increase ...
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... at a sub- stantially smaller frequency, around 2-3 kHz. Were the characteristic scales in the vortical flow transposed from the model experiment to full scale using the same scal- ing laws as for a turbulent shear flow, 5 the theoretical frequency scaling factor would be 6 4/5 ≈ 4.2, leading to the same order of magnitude. Thus the bump in Fig. 11 is believed due to the same mechanism as observed in ...
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... fluctuations are measured near the wing leading-edge, in the area where the tip vor- tex formed on the slat horn is expected to impinge on the wing, between probes A3 and A5. Furthermore, the wall pressure level increases with angle of attack, as shown in Fig. 16, between 15 • and 20 • , in the frequency range 4-to-12 kHz covering the bump of Fig. 11. Proposed noise model According to the acoustic analogy, the locus of maximum wall pressure as measured previously leads to the definition of an equivalent source at the wing leading-edge, driven by the impingement of the slat horn ...
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Citations
... Using high-fidelity computational aeroacoustic simulations is prohibitively expensive during this design phase, while analytical tools are limited in their ability to model the complex flow dynamics at the flap edge [2]. Hence, current efforts are mainly concentrated on using low-order models that are informed by experimental studies (e.g., [3], [4], [5]). These models can estimate the noise radiation as a function of high-level operational parameters, such as velocity and flap deflection angle, or if the unsteady surface pressures are known a priori, but they do not provide any insight into the detailed mechanisms behind flap tip noise that can be used to design noise reduction treatments. ...
A part-span flap on a multielement wing model was tested in the Hybrid Anechoic Wind Tunnel at the University of Toronto to investigate the aeroacoustics at the flap side edge. PIV measurements were conducted along five cross planes over the flap chord, and beamforming measurements were performed for a sweep of angles of attack. The sweep of angle of attack showed little influence of this parameter on the radiated flap side edge noise. PIV measurements revealed the installation effects that influence the deployed flap aeroacoustics, including interactions with the wake from the adjacent stowed flap and the main element. The experiments were conducted at a Reynolds number of 1.4 million and a Mach number of 0.15. I. Nomenclaturê = far-field noise autospectrum = Mach number ∞ = free-stream velocity Re = chord-based Reynolds number St = Strouhal number defined with the flap chord = mean streamwise velocity = wing span = wing stowed chord = flap chord = frequency ref = reference pressure, 20 μPa = flap chordwise axis = chordwise axis = axis orthogonal to and = spanwise axis Ω = mean streamwise vorticity ℎ = geometric angle of attack in the hard-walled wind tunnel configuration = geometric angle of attack in the Kevlar-walled wind tunnel configuration = flap deflection angle
... Such a system is characterized by the generation of two separate vortices in the upstream region of the flap, i.e., one at the upper flap side contour and the other at the lower flap side contour [10]. As stated by Molin, N., (2003) [11], in general, any vortical pattern in a flow generates sound as soon as its inertia has been modified, once the corresponding change in the pressure gradients also induces density fluctuations that propagate as sound. At commonly subsonic Mach numbers, sound generation occurs as convected vortical patterns interact with solid surfaces. ...
In this research, the relationship between the parameters of a large-scale flap
model and the physics responsible for flap side-edge noise generation, one of the
most dominant sources of the airframe noise was investigated in experimental and
computational tests. Flow-field measurements were taken according to phased
microphone array techniques toward a deeper understanding of flap side-edge
noise sources and their correlations to unsteady vorticity fluctuations. Conventional
beamforming, CLEAN-SC and DAMAS methodologies provided far-field acoustic
spectra estimations and noise source mapping, and numerical investigations were
conducted by the commercial version of PowerFLOW 5.3 R
. The model used for
the tests consists of an unswept isolated flap element with representative tip details
present in a conventional medium-range transport aircraft. Different side-edge devices were assessed toward reductions in airframe noise. A perforated side-edge
treatment was also applied to the flap side-edge. Aeroacoustic tests were conducted
in the LAE-1 closed circuit wind tunnel with a closed working section at the São
Carlos School of Engineering - University of São Paulo (EESC-USP) at up to 40m=s
flow speeds and the results provided specific information about the aeroacoustic
characterization of the dominant acoustic source mechanisms of the flap model.
... Such a system is characterized by the generation of two separate vortices in the upstream region of the flap, i.e., one at the upper flap side contour and the other at the lower flap side contour (REICHENBERGER, 2016). As stated by Molin, Roger and Barre (2003), in general, any vortical pattern in a flow generates sound as soon as its inertia has been modified, since the corresponding change in the pressure gradients also induces density fluctuations that propagate as sound. At commonly subsonic Mach numbers, sound is generated when convected vortical patterns interact with solid surfaces. ...
The first bypass turbofan engines came into operation in the early 1970’s. The need for reductions in the fuel consumption affected aircraft noise positively through reductions in the jet noise. Over the past decades, the bypass ratio of turbofan engines has continuously increased and, as a result, aircraft engine noise has decreased to a level comparable to the noise originated from the turbulent flow around the airframe for take-off and landing conditions. Although aircraft have become quieter, the number of individuals affected by the aviation growth is likely to increase. Airframe noise has been currently identified as the ultimate aircraft noise barrier and many efforts devoted to its reductions have focused specifically on landing gears and high-lift devices, which are the most relevant noise contributors. Some devices have been designed to reduce flap noise, however, not all of them have been successfully tested in a detailed large-scale flap model due to their difficult implementation in real flap side-edges. This research investigates the relationship between the parameters of a large-scale flap model at 1.5×10^6 Reynolds number and the physics responsible for flap side-edge noise generation, one of the most dominant sources of the airframe noise.
... Such a system is characterized by the generation of two separate vortices in the upstream region of the flap, i.e., one at the upper flap side contour and the other at the lower flap side contour [15]. As stated by Molin, R. and Barre, S., (2003) [16], in general, any vortical pattern in a flow generates sound as soon as its inertia has been modified, once the corresponding change in the pressure gradients also induces density fluctuations that propagate as sound. At commonly subsonic Mach numbers, sound generation occurs because convected vortical patterns interact with solid surfaces. ...
... Amiet's analytical models for leading [11] and trailing [12] edges noise have been extensively used to predict noise generated by profiles (airfoil [13][14][15] , fan or propeller [16][17][18][19][20][21] ). Molin et al. successfully used both Amiet's [22] and Howe's [23] analytical models to predict noise radiated by HLD with experimental measurements as inputs. Since then, Roger and Moreau [13,24] further improved Amiet's models by accounting for some geometrical airfoil parameters as camber and thickness, and by also integrating the backscattering effect of the leading edge on trailing-edge noise. ...
... The present work extends the latter to aerodynamic and acoustic performances of a typical 3-element HLD called L1T2 in an optimization methodology based on the same parameterized approach. To be consistent with the two-dimensional flow simulations around the L1T2 HLD, only the 2D noise sources as defined by Molin et al. are considered and important 3D noise sources as the slat-cove noise or the flap sideedge noise are discarded here [22,23] . Molin et al. also showed that these 2D sources were dominant in the mid-frequency range (typically between 100 Hz and 2 kHz) by successfully comparing with acoustic flight data on the A320 and A340 aircrafts. ...
The multi-objective optimization of both aerodynamic and broadband noise characteristics of a high-lift device is studied. The optimization is based on combining a recently developed parameterized Navier-Stokes approach as a surrogate model for solution reconstructions to a genetic algorithm for Pareto front construction. The parameterized Navier-Stokes solver Turb'Opty is a high-order sensitivity method around a reference Reynolds-Averaged Navier-Stokes (RANS) flow field. The present implementation takes into account up to the second-order partial derivatives including cross-derivatives of the RANS solver with respect to the optimization parameters. Acoustic predictions are based on Amiet's airfoil models and their extensions for turbulence interaction noise and self-noise respectively. The needed temporal data are reconstructed from wall-resolved RANS simulations or estimate through the surrogate model. The use of the parameterized Navier-Stokes approach and the self-noise model are validated with both experimental and detailed simulation data
on a NACA0012 configuration. The whole optimization process is then applied to the L1T2 high-lift device. The application of these noise models seems to qualitatively capture the broadband noise generated in
gaps between the elements. The study of the Pareto front exhibits optimal solutions with the expected trends: for instance decreasing the Mach number and the camber reduces the noise and yields a lift reduction.
Details of two optimal solutions are finally provided.
... The reduction of airframe noise in general, and HLDs in particular, has been the focus of intense research since the 1990s. Many experimental, 1-8 analytical, [9][10][11][12][13][14][15][16] and numerical [17][18][19][20][21][22][23] works have been carried out in order to better understand the flow dynamics around HLDs and their noise sources. However, most studies have focused on particular geometries and associated flow conditions that are in general at low Reynolds numbers based on the clean wing chord length because of the limitations of both test facilities and detailed unsteady simulations. ...
The noise of a canonical main-element/flap High-Lift Device (HLD) is computed directly using compressible wall-resolved Large Eddy Simulation (LES). An experimental database for the chosen configuration allows to successfully validate the chosen numerical approach. Both the noise sources and the far-field acoustic pressure are shown to be well predicted. Although the two elements trailing-edge noise can be observed in the near field, the flap remains as the dominant source in the far-field. The simplicity of the studied configuration enables the comparison of the validated numerical results with a recently developed analytical model that takes into account the diffraction of the flap noise by the main-element. A 2D (with and without Kutta
condition) and a 3D (without Kutta correction) analytical formulations are compared with the numerical results. All formulations compare favorably with the numerical reference in terms of noise levels and directivities. However, the 2D formulation with a Kutta correction provides the best quantitative agreement as expected from the narrow span of the numerical domain. The recently developed analytical model is therefore a
good predictive tool for HLD, showing that it can properly account for the diffraction effect of the main element on the flap main noise source.
... Even though this seems justified as a first sight for the quadrupole sources of airfoil trailing-edge noise, no clear evidence of the precise threshold for this regime has been documented yet. The analysis of wing-flap noise reported by Roger and Pérennès [17] and related works [18,19] are also based on the same asymptotic regime for distributed dipoles close to an edge. In this case the approximation is even more questionable, except at the lowest frequencies of interest, because the flap sources are at least several centimeters away from the scattering edge and distributed over the flap chord. ...
Exact analytical solutions for the scattering of sound by the edge of a rigid half-plane and by a rigid corner in the presence of a uniform flow are considered in this work, for arbitrary source and observer locations. Exact Green's functions for the Helmholtz equation are first reviewed and implemented in a quiescent propagation space from reference expressions of the literature. The effect of uniform fluid motion is introduced in a second step and the properties of the field are discussed for point dipoles and quadrupoles. The asymptotic regime of a source close to the scattering edge/wedge and of an observer far from it in terms of acoustic wavelengths is derived in both cases. Its validity limits are assessed by comparing with the exact solutions. Typically the asymptotic directivity is imposed by Green's function but not by the source itself. This behaviour is associated with a strong enhancement of the radiation with respect to what the source would produce in free field. The amplification depends on the geometry, on the source type and on the source distance to the edge/wedge. Various applications in aeroacoustics of wall-bounded flows are addressed, more specifically dealing with high-lift device noise mechanisms, such as trailing-edge or flap side-edge noise. The asymptotic developments are used to highlight trends that are believed to play a role in airframe noise.
... More than 30 years later, Fink's model now has successors. [2][3][4][5] However, still no empirical model has been proposed to quantify flap side-edge noise and therefore, this source is not integrated in published airframe noise models. ...
... This time, however, side-lobes (which might be due to noise generated at the model and side-plates junction) greatly contaminate the noise maps. However, from the previous analysis (figure 4), it is justified to say that this noise source certainly have much lower SPL than the noise generated at the flap tip. Whence, a strong influence on integrated spectra is not A "small grid" (shown by the dashed frame in figure 7b) and a "full grid" were used for power integration consisting, as before, of the complete surface of the presented contour maps. ...
The ultimate goal of the present study is the elaboration of an empirical noise prediction
model applicable in the early development stage of low-noise aircraft. To this end,
a series of aeroacoustic tests were performed to investigate the characteristics of flap
side-edge noise. Two generic models, an isolated flap and a high-lift wing were selected
for the experiments. Measurements of sound pressure levels as well as sound directivity
were done using dedicated microphone arrays. Moreover, the acoustic investigation
was complemented by flow measurements done with a 7-hole probe. Further analysis
of the data revealed the effectiveness of the flap tip cross-flow velocity in scaling noise
spectra. The main characteristics of the noise directivity were also determined. These
results allow the formulation of a preliminary empirical prediction scheme.
... A flap side-edge noise model derived on the basis of the aforementioned analyses have been recently validated against experimental data by Molin et al. [115]. ...
A bibliographical review of the main technologies employed for the mitigation of aircraft noise is presented. According to a component-based approach, analytical and semi-empirical models of the aeroacoustic mechanisms involved in the noise generation from airframe and engine components are presented as a key element of the noise reduction technology. These models, developed in the past to investigate the influence of some design parameters on the overall acoustic levels, are nowadays powerful design tools when employed in a multi-disciplinary optimization framework. In this spirit, the recent achievements in the numerical prediction of complex aeroacoustic phenomena through CFD/CAA techniques, not addressed in this work, provide a complementary approach to experiments to improve the accuracy of the available analytical and semi-empirical models. The bibliographical style of the paper is guaranteed by a qualitative description of the underlying physical mechanisms and their mathematical idealization. The reader is therefore remanded to the cited works for a deeper analysis.
This paper assesses the comparability of aeroacoustic slat noise measurement in an open-jet, a hard-wall, and a hybrid test section configuration. The 30P30N common research model was tested in the Aeroacoustic Wind Tunnel of the University of Twente at a chord-based Reynolds number up to 1⋅106 and free-stream Mach number 0.15. Pressure distribution measurements were used to determine the aerodynamic similar condition of the flow in the slat cove. These conditions are subsequently validated by time-averaged 2D PIV measurements. The experiments show that general aspects of the flow in the slat cove are similar when the Cp distribution around the leading-edge slat element in each test section configuration is comparable. Overall, the shear layer path and reattachment point are in close agreement, showing that the aeroacoustic noise production mechanisms are comparable. Microphone phased array measurements were subsequently conducted to compare the far-field noise characteristics originating from the slat in each test section configuration. A framework is proposed to correct the acoustic measurements of each test section configuration to a standard free-field condition. Transmission loss corrections are required for the microphone measurements in the hard-wall and hybrid test section configurations, whereas a coherence loss model was validated and applied to correct the microphone measurements in the open-jet. The measured noise spectra in each test section configuration show differences up to approximately 5 dB. In general the differences were found to be smaller. The largest differences are seen for small angles of attack with noise levels in the open-jet test section showing considerably higher values than the hard-wall test section and hybrid test section results. In addition, the behavior of the vortex shedding hump in the high frequency range is different in the open-jet measurements, which could be related to the larger noise level differences at small angles of attack.
