The Experts below are selected from a list of 3852 Experts worldwide ranked by ideXlab platform
Xin Zhang - One of the best experts on this subject based on the ideXlab platform.
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on the effects of anisotropic turbulence on Leading Edge Noise
Journal of Sound and Vibration, 2021Co-Authors: Fernando Geaaguilera, Xin Zhang, James Gill, Ravish Karve, David AnglandAbstract:Abstract This paper presents an investigation on the broadband Noise produced by the interaction of anisotropic turbulence with isolated aerofoils. Computational aeroacoustic simulations are performed using a synthetic turbulence method with a linearised Euler solver. A comprehensive and fundamental parameter study on Leading Edge Noise is presented to assess the effects of aerofoil thickness, mean flow Mach number, and angle of attack in the presence of moderately anisotropic turbulence. To this end, the streamwise-to-transverse length scale ratio is varied from 0.33 to 3, which can be representative of the anisotropy in the fan wakes from aero-engines, grid-generated turbulence in open-jet wind tunnel experiments, and rotors ingesting turbulent boundary layers. Anisotropic turbulence presents a significant redistribution of the energy in the turbulence spectra in comparison with an isotropic baseline, which affects the resulting Noise spectra. It has been found that the Noise spectra are mainly influenced by the transverse velocity component for the examined anisotropic flows. The frequency at which the Noise spectrum is at a maximum only relies on the mean flow speed and the axial length scale of the anisotropic turbulent flow. Noise reduction due to aerofoil thickness at high frequencies follows a linear trend, but the amount of Noise reduction is sensitive to the anisotropy in the flow. It is shown that the contribution of the streamwise disturbances and length scale become increasingly important for thick aerofoils at high Mach numbers and for aerofoils at non-zero angle of attack.
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caa simulations of the Leading Edge Noise of a heaving airfoil
Journal of Sound and Vibration, 2020Co-Authors: Yuhao Sun, Siyang Zhong, Teng Zhou, Xun Huang, Xin ZhangAbstract:Abstract Leading Edge Noise of airfoil is a significant source of broadband Noise for both aircraft and wind turbines. In this work, the Noise generated by the interaction of incoming turbulence and a heaving airfoil was studied. Numerical experiments were performed using a hybrid computational aeroacoustics method, where the mean flow was computed by using computational fluid dynamics, and the acoustic field was obtained by solving the linearised Euler equations. Applying Fourier analysis, the periodic mean flows around the heaving airfoil can be accurately reproduced for the aeroacoustic simulations. The incoming isotropic and anisotropic turbulence was synthesised by a modified digital filter method. The effect of the heaving motion on the Leading Edge Noise was evaluated through the comparisons of far-field directivities and Noise spectra. The far-field Noise results indicate that the effect of airfoil heaving motion on the Leading Edge Noise is larger if the incoming turbulence is anisotropic. For turbulence with a larger integral length scale in the streamwise direction, more Noise is produced, while less Noise is generated when the larger integral length scale is in the transverse direction. It is expected that the proposed method and numerical results can be helpful in providing physical insights into the airfoil Leading Edge Noise under realistic conditions.
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an analytical correction to amiet s solution of airfoil Leading Edge Noise in non uniform mean flows
Journal of Fluid Mechanics, 2020Co-Authors: Siyang Zhong, Xin Zhang, Bo Peng, Xun HuangAbstract:Gust/turbulence–Leading Edge interaction is a significant source of airfoil broadband Noise. An approach often used to predict the sound is based on Amiet’s flat-plate solution. Analytical studies have been conducted to investigate the influences of airfoil geometries, non-uniform mean flows and turbulence statistics, which, however, were often too convoluted. In this work, the problem is revisited by proposing simple corrections to the standard flat-plate solution to account for the effect of non-uniform mean flows of real airfoils. A key step in the method is to use a new space–time transformation that is analogous to the Prandtl–Glauert transformation to simplify the sound governing equation with spatially varying coefficients to a classical wave equation, which is then solved using the Schwarzschild technique as in Amiet’s solution. The impacts of Mach number, wavenumber and airfoil geometry on the prediction accuracy are investigated for both single-frequency and broadband cases, and the results are compared against high-fidelity simulations. It predicts the sound reduction by the airfoil thickness, and reveals that the reduction is caused by the non-uniform streamwise velocity. The limitations of the model are discussed and the approximation errors are estimated. In general, the prediction error increases with the airfoil thickness, the sound frequency and the flow Mach number. Nevertheless, in all cases studied in this work, the proposed correction can effectively improve the prediction accuracy of the flat-plate solution much more efficiently compared to numerical solutions of the Euler equations using computational aeroacoustics.
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synthetic turbulence methods for computational aeroacoustic simulations of Leading Edge Noise
Computers & Fluids, 2017Co-Authors: Fernando Geaaguilera, James Gill, Xin ZhangAbstract:Abstract A Leading Edge Noise prediction methodology that uses an advanced digital filter method to generate synthetic turbulence is presented for efficient two- and three-dimensional simulations. The digital filter method combines the advantages of the Random Particle-Mesh method, for the mathematical background, and synthetic eddy methods, for the numerical implementation. This allows the generation of non-periodic turbulence without explicitly filtering white Noise signals, and gives a significant reduction in the number of constraint parameters and random numbers involved in comparison with previous methods. A new eddy profile is defined through a superposition of Gaussian eddies that matches a target isotropic energy spectrum. The method is used in a linearised Euler equation solver to predict turbulence-aerofoil interaction Noise from a number of configurations, including variations in aerofoil thickness, angle of attack and Mach number. A comparison with stochastic turbulence based on Fourier modes indicates that Noise predictions are independent of the choice of synthetic turbulence method, provided that streamwise and transverse turbulent velocity components are included. Nevertheless, the advanced digital filter method is advantageous due to its reduced computational cost. This paper also extends the advanced digital filter method to realise a two-dimensional turbulent flow with the key statistics of three-dimensional turbulence, which is suitable to perform low-cost Leading Edge Noise predictions that can be compared with experiments. Tests show that this approach is capable of reproducing experimental Noise measurements to within an accuracy of 3 dB, and predicts similar Noise levels to fully three-dimensional simulations.
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a sound extrapolation method for aeroacoustics far field prediction in presence of vortical waves
Journal of Fluid Mechanics, 2017Co-Authors: Siyang Zhong, Xin ZhangAbstract:Off-surface integral solutions to an inhomogeneous wave equation based on acoustic analogy could suffer from spurious wave contamination when volume integrals are ignored for computation efficiency and vortical/turbulent gusts are convected across the integration surfaces, Leading to erroneous far-field directivity predictions. Vortical gusts often exist in aerodynamic flows and it is inevitable their effects are present on the integration surface. In this work, we propose a new sound extrapolation method for acoustic far-field directivity prediction in the presence of vortical gusts, which overcomes the deficiencies in the existing methods. The Euler equations are rearranged to an alternative form in terms of fluctuation variables that contains the possible acoustical and vortical waves. Then the equations are manipulated to an inhomogeneous wave equation with source terms corresponding to surface and volume integrals. With the new formulation, spurious monopole and dipole Noise produced by vortical gusts can be suppressed on account of the solenoidal property of the vortical waves and a simple convection process. It is therefore valid to ignore the volume integrals and preserve the sound properties. The resulting new acoustic inhomogeneous convected wave equations could be solved by means of the Green’s function method. Validation and verification cases are investigated, and the proposed method shows a capacity of accurate sound prediction for these cases. The new method is also applied to the challenging airfoil Leading Edge Noise problems by injecting vortical waves into the computational domain and performing aeroacoustic studies at both subsonic and transonic speeds. In the case of a transonic airfoil Leading Edge Noise problem, shocks are present on the airfoil surface. Good agreements of the directivity patterns are obtained compared with direct computation results.
Thomas Nodelanglois - One of the best experts on this subject based on the ideXlab platform.
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including wall effects in analytical Leading Edge Noise predictions
AIAA CEAS Aeroacoustics Conference, 2017Co-Authors: Ravish Karve, James Gill, Fernando Gea Aguilera, David Angland, Thomas NodelangloisAbstract:An analytical solution to Leading-Edge Noise produced by a translating two-dimensional flat plate ingesting turbulence in proximity to a hard-wall is presented. This is a relevant problem to calculate the installation Noise of open rotors and un-ducted fans. The analytical solution to the problem is given by using Amiet’s flat plate theory in conjunction with the Method Of Images (MOI) to include the effects of the wall. The low frequency, low Mach number limit of the analytical solution is investigated and it is shown that the flat plate in this limit behaves like a compact vertical dipole. The analytical solution is verified by a Computational AeroAcoustic (CAA) simulation that also uses the MOI to simulate a wall. While the MOI gives an approximation of the wall, it does not model all of the effects, such as diffraction from the Edges of the flat plate and acoustic shielding due to the presence of the flat plate. These effects, which are ignored in the MOI are quantified using a CAA simulation that models the wall using a hard-slip-wall boundary condition. It is found that the analytical predictions and the CAA simulations using the MOI compare well. However, when the MOI is compared to the CAA simulation using a hard-slip-wall boundary condition, it is found that the MOI does not capture the effect of the shadow zone that is created due to the shielding effect of the aerofoil. The extent of the shadow zone is modified by changing the height of the aerofoil from the wall, and it shown that as the height of the aerofoil from the wall is increased, the shielding effect decreases.
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Leading Edge Noise predictions using anisotropic synthetic turbulence
AIAA CEAS Aeroacoustics Conference, 2016Co-Authors: Fernando Gea Aguilera, Xin Zhang, James Gill, Xiaoxian Chen, Thomas NodelangloisAbstract:An advanced digital filter method is presented to generate divergence-free synthetic turbulence with homogeneous anisotropic velocity spectra. The resulting fluctuating velocity field is obtained through a superposition of anisotropic Gaussian eddies. This method is used to generate a two-dimensional turbulent flow with the key statistics of homogeneous axisymmetric turbulence. This type of turbulence has been reported in aero-engine intakes, fan wakes and open-jet wind tunnel experiments. The advanced digital filter method is implemented in a linearized Euler solver in order to investigate potential effects of anisotropic turbulence on Leading Edge Noise. Computational aeroacoustic simulations are performed for anisotropic turbulence with streamwise-to-transverse length scale ratios ranging from 0.33 to 3 on a number of isolated airfoil configurations, including variations in mean flow Mach number, airfoil thickness and angle of attack. Noise reduction due to airfoil thickness is assessed on a NACA 0012 airfoil at zero angle of attack, showing similar trends for both isotropic and moderately anisotropic turbulent flows. Effects of anisotropic turbulence on Noise become evident for airfoil configurations at non-zero angle of attack.
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synthetic turbulence methods for Leading Edge Noise predictions
AIAA CEAS Aeroacoustics Conference, 2015Co-Authors: Fernando Geaaguilera, Xin Zhang, James Gill, Xiaoxian Chen, Thomas NodelangloisAbstract:An advanced digital filter method to generate synthetic turbulence is presented for efficient two- and three-dimensional Leading Edge Noise predictions. The technique, which is based on the Random Particle-Mesh method, produces a turbulent inflow that matches a target isotropic energy spectrum. The discretized equations for the synthetic eddies, and the input parameters needed to recover the desired turbulence statistics, are presented. Moreover, a simple and fast implementation strategy, which does not require an additional boundary condition, is presented under the frozen turbulence assumption. The method is used in a linearized Euler solver to predict turbulence-airfoil interaction Noise from a number of configurations, including variations in airfoil thickness, angle of attack and Mach number. For the first time, Noise predictions from a digital filter method are directly compared to those provided by synthetic turbulence based on a summation of Fourier modes. The comparison indicates that the advanced digital filter method gives enhanced performance in terms of computational cost and simulation accuracy. In addition, initial tests show that this method is capable of reproducing experimental Noise measurements within 3 dB accuracy.
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reduced dimension modeling of Leading Edge turbulent interaction Noise
AIAA CEAS Aeroacoustics Conference, 2014Co-Authors: James Gill, Xin Zhang, Phillip Joseph, Thomas NodelangloisAbstract:A computational aeroacoustics approach is used to model the effects of real airfoil geometry on Leading Edge turbulent interaction Noise for symmetric airfoils at zero angle of attack. For the first time, one-component (transverse), two-component (transverse and streamwise), and three-component (transverse, streamwise, and spanwise) synthesized turbulent disturbances are modeled instead of single frequency transverse gusts, which previous computational studies of Leading Edge Noise have been confined to. The effects of the inclusion of streamwise and spanwise disturbances on the Noise are assessed, and it is shown that accurate Noise predictions for symmetric airfoils can be made by modeling only the transverse disturbances, which reduces the computational expense of simulations. Additionally, the two-component turbulent synthesis method is used to model the effects of airfoil thickness on the Noise for thicknesses ranging from 2% to 12%. By using sufficient airfoil thicknesses to show trends, it is found that airfoil thickness will reduce the Noise at high frequency, and that the sound power P will reduce linearly with increasing airfoil thickness.
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effects of real airfoil geometry on Leading Edge gust interaction Noise
AIAA CEAS Aeroacoustics Conference, 2013Co-Authors: James Gill, Xin Zhang, Phillip Joseph, Thomas NodelangloisAbstract:High-order computational aeroacoustic methods are applied to the modeling of Noise due to interactions between gusts and the Leading Edge of real symmetric airfoils. The effects of airfoil thickness and Leading Edge radius on Noise are investigated systematically and in-dependently for the first time, at higher frequencies than previously used in computational methods. Single frequency harmonic gusts are interacted with airfoils of varying geometry at zero angle of attack. Increases in both Leading Edge radius and thickness are found to reduce the predicted Noise. This Noise reduction effect becomes greater with increasing frequency and Mach number. The dominant Noise reduction mechanism for airfoils with real geometry is found to be related to the Leading Edge stagnation region. The assumption of uniform meanflow is shown to be invalid when modeling the Leading Edge Noise of real airfoils. However, accurate results are still obtained when an inviscid meanflow is assumed. The accuracy of analytic flat plate solutions can be expected to decrease with increasing airfoil thickness, Leading Edge radius, gust frequency and Mach number.
James Gill - One of the best experts on this subject based on the ideXlab platform.
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on the effects of anisotropic turbulence on Leading Edge Noise
Journal of Sound and Vibration, 2021Co-Authors: Fernando Geaaguilera, Xin Zhang, James Gill, Ravish Karve, David AnglandAbstract:Abstract This paper presents an investigation on the broadband Noise produced by the interaction of anisotropic turbulence with isolated aerofoils. Computational aeroacoustic simulations are performed using a synthetic turbulence method with a linearised Euler solver. A comprehensive and fundamental parameter study on Leading Edge Noise is presented to assess the effects of aerofoil thickness, mean flow Mach number, and angle of attack in the presence of moderately anisotropic turbulence. To this end, the streamwise-to-transverse length scale ratio is varied from 0.33 to 3, which can be representative of the anisotropy in the fan wakes from aero-engines, grid-generated turbulence in open-jet wind tunnel experiments, and rotors ingesting turbulent boundary layers. Anisotropic turbulence presents a significant redistribution of the energy in the turbulence spectra in comparison with an isotropic baseline, which affects the resulting Noise spectra. It has been found that the Noise spectra are mainly influenced by the transverse velocity component for the examined anisotropic flows. The frequency at which the Noise spectrum is at a maximum only relies on the mean flow speed and the axial length scale of the anisotropic turbulent flow. Noise reduction due to aerofoil thickness at high frequencies follows a linear trend, but the amount of Noise reduction is sensitive to the anisotropy in the flow. It is shown that the contribution of the streamwise disturbances and length scale become increasingly important for thick aerofoils at high Mach numbers and for aerofoils at non-zero angle of attack.
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synthetic turbulence methods for computational aeroacoustic simulations of Leading Edge Noise
Computers & Fluids, 2017Co-Authors: Fernando Geaaguilera, James Gill, Xin ZhangAbstract:Abstract A Leading Edge Noise prediction methodology that uses an advanced digital filter method to generate synthetic turbulence is presented for efficient two- and three-dimensional simulations. The digital filter method combines the advantages of the Random Particle-Mesh method, for the mathematical background, and synthetic eddy methods, for the numerical implementation. This allows the generation of non-periodic turbulence without explicitly filtering white Noise signals, and gives a significant reduction in the number of constraint parameters and random numbers involved in comparison with previous methods. A new eddy profile is defined through a superposition of Gaussian eddies that matches a target isotropic energy spectrum. The method is used in a linearised Euler equation solver to predict turbulence-aerofoil interaction Noise from a number of configurations, including variations in aerofoil thickness, angle of attack and Mach number. A comparison with stochastic turbulence based on Fourier modes indicates that Noise predictions are independent of the choice of synthetic turbulence method, provided that streamwise and transverse turbulent velocity components are included. Nevertheless, the advanced digital filter method is advantageous due to its reduced computational cost. This paper also extends the advanced digital filter method to realise a two-dimensional turbulent flow with the key statistics of three-dimensional turbulence, which is suitable to perform low-cost Leading Edge Noise predictions that can be compared with experiments. Tests show that this approach is capable of reproducing experimental Noise measurements to within an accuracy of 3 dB, and predicts similar Noise levels to fully three-dimensional simulations.
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including wall effects in analytical Leading Edge Noise predictions
AIAA CEAS Aeroacoustics Conference, 2017Co-Authors: Ravish Karve, James Gill, Fernando Gea Aguilera, David Angland, Thomas NodelangloisAbstract:An analytical solution to Leading-Edge Noise produced by a translating two-dimensional flat plate ingesting turbulence in proximity to a hard-wall is presented. This is a relevant problem to calculate the installation Noise of open rotors and un-ducted fans. The analytical solution to the problem is given by using Amiet’s flat plate theory in conjunction with the Method Of Images (MOI) to include the effects of the wall. The low frequency, low Mach number limit of the analytical solution is investigated and it is shown that the flat plate in this limit behaves like a compact vertical dipole. The analytical solution is verified by a Computational AeroAcoustic (CAA) simulation that also uses the MOI to simulate a wall. While the MOI gives an approximation of the wall, it does not model all of the effects, such as diffraction from the Edges of the flat plate and acoustic shielding due to the presence of the flat plate. These effects, which are ignored in the MOI are quantified using a CAA simulation that models the wall using a hard-slip-wall boundary condition. It is found that the analytical predictions and the CAA simulations using the MOI compare well. However, when the MOI is compared to the CAA simulation using a hard-slip-wall boundary condition, it is found that the MOI does not capture the effect of the shadow zone that is created due to the shielding effect of the aerofoil. The extent of the shadow zone is modified by changing the height of the aerofoil from the wall, and it shown that as the height of the aerofoil from the wall is increased, the shielding effect decreases.
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Leading Edge Noise predictions using anisotropic synthetic turbulence
AIAA CEAS Aeroacoustics Conference, 2016Co-Authors: Fernando Gea Aguilera, Xin Zhang, James Gill, Xiaoxian Chen, Thomas NodelangloisAbstract:An advanced digital filter method is presented to generate divergence-free synthetic turbulence with homogeneous anisotropic velocity spectra. The resulting fluctuating velocity field is obtained through a superposition of anisotropic Gaussian eddies. This method is used to generate a two-dimensional turbulent flow with the key statistics of homogeneous axisymmetric turbulence. This type of turbulence has been reported in aero-engine intakes, fan wakes and open-jet wind tunnel experiments. The advanced digital filter method is implemented in a linearized Euler solver in order to investigate potential effects of anisotropic turbulence on Leading Edge Noise. Computational aeroacoustic simulations are performed for anisotropic turbulence with streamwise-to-transverse length scale ratios ranging from 0.33 to 3 on a number of isolated airfoil configurations, including variations in mean flow Mach number, airfoil thickness and angle of attack. Noise reduction due to airfoil thickness is assessed on a NACA 0012 airfoil at zero angle of attack, showing similar trends for both isotropic and moderately anisotropic turbulent flows. Effects of anisotropic turbulence on Noise become evident for airfoil configurations at non-zero angle of attack.
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synthetic turbulence methods for Leading Edge Noise predictions
AIAA CEAS Aeroacoustics Conference, 2015Co-Authors: Fernando Geaaguilera, Xin Zhang, James Gill, Xiaoxian Chen, Thomas NodelangloisAbstract:An advanced digital filter method to generate synthetic turbulence is presented for efficient two- and three-dimensional Leading Edge Noise predictions. The technique, which is based on the Random Particle-Mesh method, produces a turbulent inflow that matches a target isotropic energy spectrum. The discretized equations for the synthetic eddies, and the input parameters needed to recover the desired turbulence statistics, are presented. Moreover, a simple and fast implementation strategy, which does not require an additional boundary condition, is presented under the frozen turbulence assumption. The method is used in a linearized Euler solver to predict turbulence-airfoil interaction Noise from a number of configurations, including variations in airfoil thickness, angle of attack and Mach number. For the first time, Noise predictions from a digital filter method are directly compared to those provided by synthetic turbulence based on a summation of Fourier modes. The comparison indicates that the advanced digital filter method gives enhanced performance in terms of computational cost and simulation accuracy. In addition, initial tests show that this method is capable of reproducing experimental Noise measurements within 3 dB accuracy.
Siyang Zhong - One of the best experts on this subject based on the ideXlab platform.
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caa simulations of the Leading Edge Noise of a heaving airfoil
Journal of Sound and Vibration, 2020Co-Authors: Yuhao Sun, Siyang Zhong, Teng Zhou, Xun Huang, Xin ZhangAbstract:Abstract Leading Edge Noise of airfoil is a significant source of broadband Noise for both aircraft and wind turbines. In this work, the Noise generated by the interaction of incoming turbulence and a heaving airfoil was studied. Numerical experiments were performed using a hybrid computational aeroacoustics method, where the mean flow was computed by using computational fluid dynamics, and the acoustic field was obtained by solving the linearised Euler equations. Applying Fourier analysis, the periodic mean flows around the heaving airfoil can be accurately reproduced for the aeroacoustic simulations. The incoming isotropic and anisotropic turbulence was synthesised by a modified digital filter method. The effect of the heaving motion on the Leading Edge Noise was evaluated through the comparisons of far-field directivities and Noise spectra. The far-field Noise results indicate that the effect of airfoil heaving motion on the Leading Edge Noise is larger if the incoming turbulence is anisotropic. For turbulence with a larger integral length scale in the streamwise direction, more Noise is produced, while less Noise is generated when the larger integral length scale is in the transverse direction. It is expected that the proposed method and numerical results can be helpful in providing physical insights into the airfoil Leading Edge Noise under realistic conditions.
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an analytical correction to amiet s solution of airfoil Leading Edge Noise in non uniform mean flows
Journal of Fluid Mechanics, 2020Co-Authors: Siyang Zhong, Xin Zhang, Bo Peng, Xun HuangAbstract:Gust/turbulence–Leading Edge interaction is a significant source of airfoil broadband Noise. An approach often used to predict the sound is based on Amiet’s flat-plate solution. Analytical studies have been conducted to investigate the influences of airfoil geometries, non-uniform mean flows and turbulence statistics, which, however, were often too convoluted. In this work, the problem is revisited by proposing simple corrections to the standard flat-plate solution to account for the effect of non-uniform mean flows of real airfoils. A key step in the method is to use a new space–time transformation that is analogous to the Prandtl–Glauert transformation to simplify the sound governing equation with spatially varying coefficients to a classical wave equation, which is then solved using the Schwarzschild technique as in Amiet’s solution. The impacts of Mach number, wavenumber and airfoil geometry on the prediction accuracy are investigated for both single-frequency and broadband cases, and the results are compared against high-fidelity simulations. It predicts the sound reduction by the airfoil thickness, and reveals that the reduction is caused by the non-uniform streamwise velocity. The limitations of the model are discussed and the approximation errors are estimated. In general, the prediction error increases with the airfoil thickness, the sound frequency and the flow Mach number. Nevertheless, in all cases studied in this work, the proposed correction can effectively improve the prediction accuracy of the flat-plate solution much more efficiently compared to numerical solutions of the Euler equations using computational aeroacoustics.
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a sound extrapolation method for aeroacoustics far field prediction in presence of vortical waves
Journal of Fluid Mechanics, 2017Co-Authors: Siyang Zhong, Xin ZhangAbstract:Off-surface integral solutions to an inhomogeneous wave equation based on acoustic analogy could suffer from spurious wave contamination when volume integrals are ignored for computation efficiency and vortical/turbulent gusts are convected across the integration surfaces, Leading to erroneous far-field directivity predictions. Vortical gusts often exist in aerodynamic flows and it is inevitable their effects are present on the integration surface. In this work, we propose a new sound extrapolation method for acoustic far-field directivity prediction in the presence of vortical gusts, which overcomes the deficiencies in the existing methods. The Euler equations are rearranged to an alternative form in terms of fluctuation variables that contains the possible acoustical and vortical waves. Then the equations are manipulated to an inhomogeneous wave equation with source terms corresponding to surface and volume integrals. With the new formulation, spurious monopole and dipole Noise produced by vortical gusts can be suppressed on account of the solenoidal property of the vortical waves and a simple convection process. It is therefore valid to ignore the volume integrals and preserve the sound properties. The resulting new acoustic inhomogeneous convected wave equations could be solved by means of the Green’s function method. Validation and verification cases are investigated, and the proposed method shows a capacity of accurate sound prediction for these cases. The new method is also applied to the challenging airfoil Leading Edge Noise problems by injecting vortical waves into the computational domain and performing aeroacoustic studies at both subsonic and transonic speeds. In the case of a transonic airfoil Leading Edge Noise problem, shocks are present on the airfoil surface. Good agreements of the directivity patterns are obtained compared with direct computation results.
C. J. Chapman - One of the best experts on this subject based on the ideXlab platform.
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basic singular fields in the theory of impulsive supersonic Leading Edge Noise
Wave Motion, 2019Co-Authors: C. J. Chapman, C J PowlesAbstract:Abstract This paper determines the impulsive sound fields produced by sharp-Edged gusts striking the Leading Edge of a supersonic blade or aerofoil, for example in a turbofan aeroengine or a counter-rotating propeller system. A full three-dimensional theory is provided, so that the gust Edges can be at any orientation relative to the blade. Complete details are given of the sound fields produced by gust Edges in the spanwise and streamwise directions, and by many combinations of such Edges, including corners. The mathematical theory depends on singular sound fields produced by gusts with a delta-function upwash; these are used to derive exact analytical formulae for impulsive sound fields of different three-dimensional shapes, and also a Green’s function representation of the field which is especially adapted to numerical evaluation. Gusts with top-hat profiles are given particular attention, and also the effect of Gaussian-function smoothing of both delta-function and top-hat profiles. The investigation is complementary to that in a companion paper (Powles and Chapman, 2019), which determines the smooth sound fields produced by single-frequency gusts. Fourier integration provides the relation between the two types of field.
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canonical sound fields in the frequency domain theory of supersonic Leading Edge Noise
Wave Motion, 2019Co-Authors: C J Powles, C. J. ChapmanAbstract:Abstract This paper determines the three-dimensional structure of certain single-frequency canonical sound fields occurring in the theory of blade–vortex interaction when the flow velocity relative to the blade is supersonic. A relative velocity of this magnitude occurs at the outer part of the fan blades in an aeroengine, at which the incoming vorticity has either been ingested from the atmosphere or created in the aeroengine itself. The sound fields analysed are those produced by the Leading Edge of a flat-plate blade at zero angle of attack on being struck by a gust which is either (i) localized along the span, or (ii) non-localized but discontinuous. The canonical gusts of type (i) have either a delta-function or Gaussian shape, and those of type (ii) are either anti-symmetric or described by a Heaviside function; these gusts give rise to the four basic canonical sound fields. The paper also analyses a fifth sound field, produced by a single-frequency top-hat gust. This sound field has a complex structure involving aspects of both (i) and (ii), but can nevertheless be analysed in terms of the canonical sound fields. The main results of the paper are exact and approximate analytical formulae giving the dependence of the acoustic field on gust-shape and flow parameters, and also a simple formula which is ideal for numerical work. The last of these is used to assess in detail the numerical accuracy of all the approximate formulae, which are of either Fresnel or Keller type. A key result is that Keller-type formulae, representing sound rays produced in accord with the geometrical theory of diffraction, have a very wide range of validity. A companion paper (Chapman & Powles 2019) determines the canonical sound fields in the corresponding time-domain theory.
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high speed Leading Edge Noise
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2003Co-Authors: C. J. ChapmanAbstract:This paper determines the sound generated at the Leading Edge of a turbofan blade in a subsonic flow when the blade is struck by a convected gust of arbitrary shape. The gust may be localized in th...