The Experts below are selected from a list of 9366 Experts worldwide ranked by ideXlab platform
Phillip Joseph - One of the best experts on this subject based on the ideXlab platform.
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Determining the strength of rotating broadband Sources in ducts by inverse methods
Journal of Sound and Vibration, 2006Co-Authors: Christopher Lowis, Phillip JosephAbstract:Aeroengine broadband fan noise is a major contributor to the community noise exposure from aircraft. It is currently believed that the dominant broadband noise mechanisms are due to interaction of the turbulent wake from the rotor with the stator, and interaction of the turbulent boundary layers on the rotor blades with their trailing edges. Currently there are no measurement techniques that allow the localisation and quantification of rotor-based broadband noise Sources. This paper presents an inversion technique for estimating the broadband acoustic Source strength distribution over a ducted rotor using pressure measurements made at the duct wall. It is shown that the rotation of acoustic Sources in a duct prevents the use of standard acoustic inversion techniques. A new technique is presented here for inverting the strength of rotating broadband Sources that makes use of a new Green function taking into account the effect of Source rotation. The new Green function is used together with a modal decomposition technique to remove the effect of Source rotation, thereby allowing an estimation of the rotor-based Source strengths in the rotating reference frame. It is shown that the pressure measured at the sensors after application of this technique is identical to that measured by sensors rotating at the same speed as the rotor. Results from numerical simulations are presented to investigate the resolution limits of the inversion technique. The azimuthal resolution limit, namely the ability of the measurement technique to discriminate between Sources on adjacent blades, is shown to improve as the speed of rotation increases. To improve the robustness of the inversion technique, a simplifying assumption is made whereby the Sources on different blades are assumed to be identical. It is also shown that the accuracy and robustness of the inversion procedure improve as the axial separation between the rotor and sensors decreases. Simulation results demonstrate that for a 26-bladed fan, rotating with a blade tip Mach number of Mt=0.5, the Aerodynamic Source strengths can be estimated with acceptable robustness and approximately 1 dB accuracy, when measurements are made approximately 0.1 acoustic wavelengths from the rotor.
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Inversion technique for determining the strength of rotating broadband Sources in ducts
11th AIAA CEAS Aeroacoustics Conference, 2005Co-Authors: Christopher Lowis, Phillip JosephAbstract:Aeroengine broadband fan noise is a major contributor to the community noise exposure from aircraft. Currently there are no measurement techniques that allow the localisation and quantification of rotor-based broadband noise Sources. This paper presents an inversion technique for estimating the broadband acoustic Source strength distribution over a ducted rotor using pressure measurements made at the duct wall. It is shown that the rotation of acoustic Sources in a duct prevents the use of standard acoustic inversion techniques. The technique presented here makes use of a new Green function that takes into account the effect of Source rotation. The new Green function is used together with a modal decomposition technique to remove the effect of Source rotation, thereby allowing an estimation of the rotor-based Source strengths in the rotating reference frame. It is shown that the pressure measured at the sensors after application of this technique is identical to that measured by sensors rotating at the same speed as the rotor. Results from numerical simulations are presented to investigate the resolution limits of the inversion technique. The azimuthal resolution limit, namely the ability of the measurement technique to discriminate between Sources on adjacent blades, is shown to improve as the speed of rotation increases. To improve the robustness of the inversion technique a simplifying assumption is made whereby the Sources on different blades are assumed to be identical. It is also shown that the accuracy and robustness of the inversion procedure improve as the axial separation between the rotor and sensors decreases. Simulations demonstrate that for a 26-bladed fan, rotating at Mt = 0.5, the Aerodynamic Source strengths can be estimated with acceptable robustness and approximately 1dB accuracy, when measurements are made 0.1 acoustic wavelengths from the rotor.
Wim Desmet - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamic/Acoustic Splitting Technique for Computation Aeroacoustics Applications at Low-Mach Numbers
AIAA Journal, 2008Co-Authors: W. De Roeck, Martine Baelmans, Wim DesmetAbstract:Hybrid computational aeroacoustics applications approaches, in which the computational domain is split into an Aerodynamic Source domain and an acoustic propagation region, are commonly used for aeroacoustic engineering applications and have proven to be of acceptable efficiency and accuracy. The different coupling techniques tend to give erroneous results for a number of applications, which are mainly encountered in confined environments. Acoustic analogies are inaccurate if the acoustic variables are of the same order of magnitude as the flow variables, and an acoustic continuation of the Source-domain simulation using the latter solution as acoustic boundary conditions is only possible if no vortical outflow is occurring. These inaccuracies can be avoided by using appropriate filtering techniques in which the Source-domain solution is split into an acoustic and an Aerodynamic fluctuating part. In this paper, such an Aerodynamic/acoustic splitting technique is developed and validated for some simple test cases. The filtering method is valid for low-Mach-number applications, assuming that all compressibility effects are caused by the irrotational acoustic field and that the incompressible Aerodynamic field is responsible for the vortical movement of the flowfield. Under these assumptions, it is shown that the Aerodynamic and acoustic fields at every time step are obtained by solving a system of Poisson equations driven by the fluctuating expansion ratio and vorticity, obtained from the Source-domain simulation. For hybrid computational aeroacoustics applications approaches, this filtering technique, generally applicable for both free-field and confined-flow applications, provides more accurate coupling information and improves the knowledge of Aerodynamic-noise-generating mechanisms.
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An Aerodynamic/acoustic splitting technique for hybrid CAA applications
13th AIAA CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007Co-Authors: W. De Roeck, Martine Baelmans, Wim DesmetAbstract:Hybrid CAA-approaches, where the computational domain is split into an Aerodynamic Source domain and an acoustic propagation region, are commonly used for aeroacoustic engineering applications and have proven to be of acceptable efficiency and accuracy. The different coupling techniques tend to give erroneous results for a number of applications, which are mainly encountered in confined environments. Acoustic analogies are inaccurate, if the acoustic variables are of the same order of magnitude as the flow variables and an acoustic continuation of the Source domain simulation using the latter solution as acoustic boundary conditions is only possible if no vortical outflow is occurring. These inaccuracies can be avoided by using appropriate filtering techniques where the Source domain solution is split into an acoustic and an Aerodynamic fluctuating part. In this paper, such an Aerodynamic/acoustic splitting technique is developed and validated for some simple test cases. The filtering method is valid for low-Mach number applications, assuming that all compressibility effects are caused by the irrotational acoustic field while the incompressible Aerodynamic field is responsible for the vortical movement of the flow field. Under these assumptions, it is shown that the Aerodynamic and acoustic fields at every time step are obtained by solving a system of Poisson equations driven by the fluctuating expansion ratio and vorticity, obtained form the Source domain simulation. For hybrid CAA-approaches this filtering technique, general applicable for both free-field and confined flow applications, is able to provide more accurate coupling information and improves the knowledge of Aerodynamic noise generating mechanisms.
Kim - One of the best experts on this subject based on the ideXlab platform.
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Numerical Analysis and Characterization of Surface Pressure Fluctuations of High-Speed Trains Using Wavenumber–Frequency Analysis
Applied Sciences, 2019Co-Authors: Lee, Cheong, KimAbstract:The high-speed train interior noise induced by the exterior flow field is one of the critical issues for product developers to consider during design. The reliable numerical prediction of noise in a passenger cabin due to exterior flow requires the decomposition of surface pressure fluctuations into the hydrodynamic (incompressible) and the acoustic (compressible) components, as well as the accurate computation of the near aeroacoustic field, since the transmission characteristics of incompressible and compressible pressure waves through the wall panel of the cabin are quite different from each other. In this paper, a systematic numerical methodology is presented to obtain separate incompressible and compressible surface pressure fields in the wavenumber–frequency and space–time domains. First, large eddy simulation techniques were employed to predict the exterior flow field, including a highly-resolved acoustic near-field, around a high-speed train running at the speed of 300 km/h in an open field. Pressure fluctuations on the train surface were then decomposed into incompressible and compressible fluctuations using the wavenumber–frequency analysis. Finally, the separated incompressible and compressible surface pressure fields were obtained from the inverse Fourier transform of the wavenumber–frequency spectrum. The current method was illustratively applied to the high-speed train HEMU-430X running at a speed of 300 km/h in an open field. The results showed that the separate incompressible and compressible surface pressure fields in the time–space domain could be obtained together with the associated Aerodynamic Source mechanism. The power levels due to each pressure field were also estimated, and these can be directly used for interior noise prediction.
Florent Margnat - One of the best experts on this subject based on the ideXlab platform.
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Numerical study of Mach number and thermal effects on sound radiation by a mixing layer
International Journal of Aeroacoustics, 2012Co-Authors: C. Moser, Eric Lamballais, Florent Margnat, Véronique Fortuné, Yves GervaisAbstract:Mach number and thermal effects on the mechanisms of sound generation and propagation are investigated in spatially evolving two-dimensional isothermal and non-isothermal mixing layers at Mach number ranging from 0.2 to 0.4 and Reynolds number of 400. A characteristic-based formulation is used to solve by direct numerical simulation the compressible Navier-Stokes equations using high-order schemes. The radiated sound is directly computed in a domain that includes both the near-field Aerodynamic Source region and the far-field sound propagation. In the isothermal mixing layer, Mach number effects may be identified in the acoustic field through an increase of the directivity associated with the non-compactness of the acoustic Sources. Baroclinic instability effects may be recognized in the non-isothermal mixing layer, as the presence of counter-rotating vorticity layers, the resulting acoustic Sources being found less efficient. An analysis based on the acoustic analogy shows that the directivity increase w...
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A Mixing-Layer Flow Noise Analysis by Retarded-time Filtering of the Source Field
2010Co-Authors: Florent MargnatAbstract:To date, the physical phenomenon that converts kinetic energy into acoustic waves escaping from the flow is not fully understood. Thanks to the increasing computational power, aeroacoustic prediction tools have become more and more fast and accurate. however, it is still challenging to link an acoustic emission pattern to the Aerodynamic Source field, in terms of causal events. Lighthill's acoustic analogy provides a way to extract the propagative motion from a flow through the expression of Source term in an inhomogeneous wave equation. Unfortunately, when the flow is not compact, Source field visualisations hardly exhibits flow locations where the acoustic energy could be produced. In the present contribution, we study the Source field considered at the retarded-time, which is the true radiating quantity. It differs from the fixed-time Source field because it takes into account the solution of the wave equation, usually expressed by a Green function. This methodology is applied to a 2D spatially evolving mixing-layer at Re=400 and 0.375 convective Mach number. Areas in the Source domain are analysed by evaluating their net contribution to the aeroacoustic integral, and destructive interferences are noticed between non-radiating areas.
Christopher Lowis - One of the best experts on this subject based on the ideXlab platform.
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Determining the strength of rotating broadband Sources in ducts by inverse methods
Journal of Sound and Vibration, 2006Co-Authors: Christopher Lowis, Phillip JosephAbstract:Aeroengine broadband fan noise is a major contributor to the community noise exposure from aircraft. It is currently believed that the dominant broadband noise mechanisms are due to interaction of the turbulent wake from the rotor with the stator, and interaction of the turbulent boundary layers on the rotor blades with their trailing edges. Currently there are no measurement techniques that allow the localisation and quantification of rotor-based broadband noise Sources. This paper presents an inversion technique for estimating the broadband acoustic Source strength distribution over a ducted rotor using pressure measurements made at the duct wall. It is shown that the rotation of acoustic Sources in a duct prevents the use of standard acoustic inversion techniques. A new technique is presented here for inverting the strength of rotating broadband Sources that makes use of a new Green function taking into account the effect of Source rotation. The new Green function is used together with a modal decomposition technique to remove the effect of Source rotation, thereby allowing an estimation of the rotor-based Source strengths in the rotating reference frame. It is shown that the pressure measured at the sensors after application of this technique is identical to that measured by sensors rotating at the same speed as the rotor. Results from numerical simulations are presented to investigate the resolution limits of the inversion technique. The azimuthal resolution limit, namely the ability of the measurement technique to discriminate between Sources on adjacent blades, is shown to improve as the speed of rotation increases. To improve the robustness of the inversion technique, a simplifying assumption is made whereby the Sources on different blades are assumed to be identical. It is also shown that the accuracy and robustness of the inversion procedure improve as the axial separation between the rotor and sensors decreases. Simulation results demonstrate that for a 26-bladed fan, rotating with a blade tip Mach number of Mt=0.5, the Aerodynamic Source strengths can be estimated with acceptable robustness and approximately 1 dB accuracy, when measurements are made approximately 0.1 acoustic wavelengths from the rotor.
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Inversion technique for determining the strength of rotating broadband Sources in ducts
11th AIAA CEAS Aeroacoustics Conference, 2005Co-Authors: Christopher Lowis, Phillip JosephAbstract:Aeroengine broadband fan noise is a major contributor to the community noise exposure from aircraft. Currently there are no measurement techniques that allow the localisation and quantification of rotor-based broadband noise Sources. This paper presents an inversion technique for estimating the broadband acoustic Source strength distribution over a ducted rotor using pressure measurements made at the duct wall. It is shown that the rotation of acoustic Sources in a duct prevents the use of standard acoustic inversion techniques. The technique presented here makes use of a new Green function that takes into account the effect of Source rotation. The new Green function is used together with a modal decomposition technique to remove the effect of Source rotation, thereby allowing an estimation of the rotor-based Source strengths in the rotating reference frame. It is shown that the pressure measured at the sensors after application of this technique is identical to that measured by sensors rotating at the same speed as the rotor. Results from numerical simulations are presented to investigate the resolution limits of the inversion technique. The azimuthal resolution limit, namely the ability of the measurement technique to discriminate between Sources on adjacent blades, is shown to improve as the speed of rotation increases. To improve the robustness of the inversion technique a simplifying assumption is made whereby the Sources on different blades are assumed to be identical. It is also shown that the accuracy and robustness of the inversion procedure improve as the axial separation between the rotor and sensors decreases. Simulations demonstrate that for a 26-bladed fan, rotating at Mt = 0.5, the Aerodynamic Source strengths can be estimated with acceptable robustness and approximately 1dB accuracy, when measurements are made 0.1 acoustic wavelengths from the rotor.
