Pub Date : 2022-09-01DOI: 10.1177/1475472X221107363
S. Rienstra
An old model problem for the exchange of energy between sound field and mean flow by vortex shedding has been worked out in numerical detail. The analytically exact solution of the problem of reflection, diffraction and radiation of acoustic modes in a semi-infinite annular duct with uniform subsonic mean flow, including shedding of unsteady vorticity from the duct exit, allows a precise formulation of Myers’ energy for perturbations of an inviscid mean flow. The transmitted power P t in the duct and the radiated power P f in the far field differ by the amounts of hydrodynamic far field powers P H i inside and P H o outside the wake (vortex sheet) emanating from the duct edge, plus the power P w that disappears into the vortex sheet. This last component represents the source term in Myers’ energy equation. This is evidence of the non-conserved character of acoustic energy in mean flow, owing to the coupling of the acoustic field with the mean flow. P f , P H i and P H o are always positive. This is normally the case too for P w and P t . But for not too high frequencies or other circumstances where shed vorticity produces more sound than was necessary for its creation, P w and even P t may also be negative.
本文对涡旋脱落声场与平均流能量交换的一个老模型问题进行了数值计算。具有均匀亚音速平均流的半无限环形管道中声模的反射、衍射和辐射问题的解析精确解，包括管道出口的非定常涡量的脱落，允许对无粘平均流的扰动的迈尔斯能量的精确公式。管道内的传输功率pt和远场辐射功率pf的差异在于，从管道边缘发出的尾迹(旋涡片)内部和外部的流体动力远场功率ph i的量加上消失在旋涡片中的功率pw。最后一个分量表示Myers能量方程中的源项。由于声场与平均流的耦合作用，声能在平均流中具有非守恒性。P f, P H i和P H o总是正的。对于pw和pt通常也是这样。但如果频率不太高，或者在其他情况下，流涡产生的声音比产生它所必需的声音要多，那么pw甚至pt也可能是负的。
{"title":"Acoustic energy balances for sound radiated from duct exit with mean flow","authors":"S. Rienstra","doi":"10.1177/1475472X221107363","DOIUrl":"https://doi.org/10.1177/1475472X221107363","url":null,"abstract":"An old model problem for the exchange of energy between sound field and mean flow by vortex shedding has been worked out in numerical detail. The analytically exact solution of the problem of reflection, diffraction and radiation of acoustic modes in a semi-infinite annular duct with uniform subsonic mean flow, including shedding of unsteady vorticity from the duct exit, allows a precise formulation of Myers’ energy for perturbations of an inviscid mean flow. The transmitted power P t in the duct and the radiated power P f in the far field differ by the amounts of hydrodynamic far field powers P H i inside and P H o outside the wake (vortex sheet) emanating from the duct edge, plus the power P w that disappears into the vortex sheet. This last component represents the source term in Myers’ energy equation. This is evidence of the non-conserved character of acoustic energy in mean flow, owing to the coupling of the acoustic field with the mean flow. P f , P H i and P H o are always positive. This is normally the case too for P w and P t . But for not too high frequencies or other circumstances where shed vorticity produces more sound than was necessary for its creation, P w and even P t may also be negative.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"410 - 429"},"PeriodicalIF":1.0,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42069001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-01DOI: 10.1177/1475472X221107374
Tomoaki Ikeda, K. Yamamoto
In the present article, frequency-domain formulations of quadrupole corrections are derived in a computationally efficient form for the Ffowcs Williams and Hawkings (FW-H) equation with permeable control surfaces. Quadrupole corrections effectively reduce spurious noise associated with hydrodynamic fluctuations passing across integral surfaces, originally derived for Formulation 1A of Farassat in the time domain. When a corresponding frequency-domain formulation is sought, however, difficulty arises as its Green’s function is written in a convective form and different from that of Formulation 1A. First, the mathematical framework of the convective FW-H equation is shown to be equivalent to Formulation 1A by applying a simple Galilean transformation for rectilinear motion. Then, a frequency-domain formulation is derived via a Fourier transform applied directly to the time-domain quadrupole correction forms. The results of the derived formulation agree precisely with the time-domain solutions, in the verification study of vortex convection, as well as non-uniform entropy convection, in which spurious noise can be effectively removed by the present quadrupole correction integrals.
{"title":"Computationally efficient, frequency-domain quadrupole corrections for the Ffowcs Williams and Hawkings equation","authors":"Tomoaki Ikeda, K. Yamamoto","doi":"10.1177/1475472X221107374","DOIUrl":"https://doi.org/10.1177/1475472X221107374","url":null,"abstract":"In the present article, frequency-domain formulations of quadrupole corrections are derived in a computationally efficient form for the Ffowcs Williams and Hawkings (FW-H) equation with permeable control surfaces. Quadrupole corrections effectively reduce spurious noise associated with hydrodynamic fluctuations passing across integral surfaces, originally derived for Formulation 1A of Farassat in the time domain. When a corresponding frequency-domain formulation is sought, however, difficulty arises as its Green’s function is written in a convective form and different from that of Formulation 1A. First, the mathematical framework of the convective FW-H equation is shown to be equivalent to Formulation 1A by applying a simple Galilean transformation for rectilinear motion. Then, a frequency-domain formulation is derived via a Fourier transform applied directly to the time-domain quadrupole correction forms. The results of the derived formulation agree precisely with the time-domain solutions, in the verification study of vortex convection, as well as non-uniform entropy convection, in which spurious noise can be effectively removed by the present quadrupole correction integrals.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"610 - 625"},"PeriodicalIF":1.0,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45933537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-01DOI: 10.1177/1475472X221107370
Nick P Breen, K. Ahuja
Over the years, there have been numerous studies on determining subsonic jet noise source locations, typically plotted as Strouhal number as a function of distance from the nozzle exit. A comparison of the results of various studies yields a spread of about two nozzle diameters in measured source location. This work examines how boundary layer thickness, which can vary from nozzle to nozzle, could be the cause of observed differences in different studies in subsonic jet noise source location. Source location measurements of unheated jets from ASME nozzles, which have comparably thinner nozzle exit boundary layers, and conical nozzles, which have comparably thicker nozzle exit boundary layers, are compared. These results are substantiated with the use of schlieren flow visualization and velocity profile measurements. It is found that the nozzles with thinner nozzle exit boundary layers have noise source distributions that are 0.25–2 diameters upstream of those with thicker nozzle exit boundary layers. Thinner nozzle exit boundary layers result in higher growth rates of instability waves, increasing mixing and thereby moving noise sources upstream.
{"title":"Subsonic jet noise source location as a function of nozzle exit boundary layer","authors":"Nick P Breen, K. Ahuja","doi":"10.1177/1475472X221107370","DOIUrl":"https://doi.org/10.1177/1475472X221107370","url":null,"abstract":"Over the years, there have been numerous studies on determining subsonic jet noise source locations, typically plotted as Strouhal number as a function of distance from the nozzle exit. A comparison of the results of various studies yields a spread of about two nozzle diameters in measured source location. This work examines how boundary layer thickness, which can vary from nozzle to nozzle, could be the cause of observed differences in different studies in subsonic jet noise source location. Source location measurements of unheated jets from ASME nozzles, which have comparably thinner nozzle exit boundary layers, and conical nozzles, which have comparably thicker nozzle exit boundary layers, are compared. These results are substantiated with the use of schlieren flow visualization and velocity profile measurements. It is found that the nozzles with thinner nozzle exit boundary layers have noise source distributions that are 0.25–2 diameters upstream of those with thicker nozzle exit boundary layers. Thinner nozzle exit boundary layers result in higher growth rates of instability waves, increasing mixing and thereby moving noise sources upstream.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"537 - 557"},"PeriodicalIF":1.0,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42878276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-01DOI: 10.1177/1475472X221107365
J. Delfs, M. Mößner, S. Proskurov, R. Ewert
In appreciation of Ffowcs-Williams and Hawkings’ seminal contribution on describing the sound radiation from moving objects, this article discusses a concept of taking into account local non-trivial flow effects on the sound propagation. The approach is motivated by the fact that the numerical simulation of the sound propagation from complete full scale aircraft by means of volume-discretizing (CAA = Computational AeroAcoustics) methods is prohibitively expensive. In fact, a homogeneous use of such CAA approach would waste computational resources since for low speed conditions the sound propagation around the aircraft is subject to very mild flow effects almost everywhere and may be treated by more inexpensive methods. The part of the domain, where the sound propagation is subject to strong flow effects and thus requiring the use of CAA is quite restricted. These circumstances may be exploited given a consistent coupling of methods. The proposed concept is based on the strong (alternatively weak) coupling of a volume discretizing solver for the Acoustic Perturbation Equations (APE) and a modified Ffowcs-Williams and Hawkings (FW-H) type acoustic integral. The approach is established in the frequency domain and requires two basic ingredients, namely a) a volume discretizing solver for the APE, or for Möhring-Howe’s aeroacoustic analogy, to take into account strong non trivial flow effects like refraction at shear flows wherever necessary, and b) an aeroacoustic integral equation for the propagation part in areas where non-potential mean flow effects are negligible. The coupling of this aeroacoustic integral and the APE solver may be realized in a strong (i.e. two-ways) form in which both components feed back information into one another, or in a weak form (i.e. one-way), in which the sound field output data from the APE solver serves as given input for the integral equation. If an aircraft geometry has minor influence on the sound radiation to arbitrary observer positions, the aeroacoustic integrals may simply be evaluated explicitly. If on the other hand, the presence of the geometry has an important influence on the sound radiation, then the acoustic integral equation is implicit and requires some sort of numerical solution, in this case a Fast Multipole Boundary Element solver. While conceptually the weak coupling follows the spirit of the FW-H approach to describe sound propagation from aeroacoustic sources the underlying aeroacoustic integral is not based on Lighthill’s analogy, but the aeroacoustic analogy of Möhring-Howe. This is a consequence of the fact that in the two way-coupling the acoustic particle velocity in a moving medium needs to be determined, which is non-trivial based on an acoustic integral. As an important feature of the strong coupling the acoustic integral also provides practically perfect non-reflection boundary conditions even when the desireably small CAA domain does not extend into the far field. The validity of the p
{"title":"Extension of the concept of Ffowcs-Williams and Hawkings type wave extrapolation to non-trivial flow effects and exterior surfaces","authors":"J. Delfs, M. Mößner, S. Proskurov, R. Ewert","doi":"10.1177/1475472X221107365","DOIUrl":"https://doi.org/10.1177/1475472X221107365","url":null,"abstract":"In appreciation of Ffowcs-Williams and Hawkings’ seminal contribution on describing the sound radiation from moving objects, this article discusses a concept of taking into account local non-trivial flow effects on the sound propagation. The approach is motivated by the fact that the numerical simulation of the sound propagation from complete full scale aircraft by means of volume-discretizing (CAA = Computational AeroAcoustics) methods is prohibitively expensive. In fact, a homogeneous use of such CAA approach would waste computational resources since for low speed conditions the sound propagation around the aircraft is subject to very mild flow effects almost everywhere and may be treated by more inexpensive methods. The part of the domain, where the sound propagation is subject to strong flow effects and thus requiring the use of CAA is quite restricted. These circumstances may be exploited given a consistent coupling of methods. The proposed concept is based on the strong (alternatively weak) coupling of a volume discretizing solver for the Acoustic Perturbation Equations (APE) and a modified Ffowcs-Williams and Hawkings (FW-H) type acoustic integral. The approach is established in the frequency domain and requires two basic ingredients, namely a) a volume discretizing solver for the APE, or for Möhring-Howe’s aeroacoustic analogy, to take into account strong non trivial flow effects like refraction at shear flows wherever necessary, and b) an aeroacoustic integral equation for the propagation part in areas where non-potential mean flow effects are negligible. The coupling of this aeroacoustic integral and the APE solver may be realized in a strong (i.e. two-ways) form in which both components feed back information into one another, or in a weak form (i.e. one-way), in which the sound field output data from the APE solver serves as given input for the integral equation. If an aircraft geometry has minor influence on the sound radiation to arbitrary observer positions, the aeroacoustic integrals may simply be evaluated explicitly. If on the other hand, the presence of the geometry has an important influence on the sound radiation, then the acoustic integral equation is implicit and requires some sort of numerical solution, in this case a Fast Multipole Boundary Element solver. While conceptually the weak coupling follows the spirit of the FW-H approach to describe sound propagation from aeroacoustic sources the underlying aeroacoustic integral is not based on Lighthill’s analogy, but the aeroacoustic analogy of Möhring-Howe. This is a consequence of the fact that in the two way-coupling the acoustic particle velocity in a moving medium needs to be determined, which is non-trivial based on an acoustic integral. As an important feature of the strong coupling the acoustic integral also provides practically perfect non-reflection boundary conditions even when the desireably small CAA domain does not extend into the far field. The validity of the p","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"501 - 520"},"PeriodicalIF":1.0,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47152784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-11DOI: 10.1177/1475472X221107497
S. Glegg, Máté Szőke, W. Devenport
In this paper we will develop a model for the acoustic transmission loss and self-noise generated by a Kevlar wind tunnel wall. It is shown that the porosity of the fabric is the most important controlling factor of the transmission loss, and the effect of wind tunnel flow speed is to increase the losses, as observed in experiments. In addition, a model is developed for the weave noise generated by a Kevlar wind tunnel wall, which is found to be caused by the pumping of the fluid through the pores in the Kevlar and depends on their open area ratio. The mechanism for this sound generation is similar to the roughness noise mechanism for a turbulent boundary layer in that the pore spacing couples with the small wavelength disturbances in the boundary layer to cause acoustic radiation at the sum and difference frequencies.
{"title":"Acoustic transmission loss and noise from Kevlar wind tunnel walls","authors":"S. Glegg, Máté Szőke, W. Devenport","doi":"10.1177/1475472X221107497","DOIUrl":"https://doi.org/10.1177/1475472X221107497","url":null,"abstract":"In this paper we will develop a model for the acoustic transmission loss and self-noise generated by a Kevlar wind tunnel wall. It is shown that the porosity of the fabric is the most important controlling factor of the transmission loss, and the effect of wind tunnel flow speed is to increase the losses, as observed in experiments. In addition, a model is developed for the weave noise generated by a Kevlar wind tunnel wall, which is found to be caused by the pumping of the fluid through the pores in the Kevlar and depends on their open area ratio. The mechanism for this sound generation is similar to the roughness noise mechanism for a turbulent boundary layer in that the pore spacing couples with the small wavelength disturbances in the boundary layer to cause acoustic radiation at the sum and difference frequencies.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"382 - 409"},"PeriodicalIF":1.0,"publicationDate":"2022-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42570460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-04DOI: 10.1177/1475472X221107366
D. Lockard
This paper considers potential sources of error when using the Ffowcs Williams-Hawkings equation to make predictions of airframe noise, which entails a relatively low-speed, uniform incoming flow encountering geometry of varying complexity. Numerical simulations are used to investigate several model problems where Ffowcs Williams-Hawkings integration surfaces are placed on solid surfaces as well as in the flow. Comparisons with the pressure obtained directly from the simulations reveal that when solid surfaces are used, the acoustic calculations can produce erroneous results in upstream directions and when scattering bodies block the line of sight from observers to the source. Using solid surface input data implies ignoring all volumetric source effects, which include noise generation as well as flow effects. Nonuniform flow alone, such as is found in a steady boundary layer, was not found to be a significant source of error, so the amplitude and phase changes induced by turbulent eddies in massively separated flow regions is speculated to be the primary cause of the error.
{"title":"Airframe noise predictions using the Ffowcs Williams-Hawkings equation","authors":"D. Lockard","doi":"10.1177/1475472X221107366","DOIUrl":"https://doi.org/10.1177/1475472X221107366","url":null,"abstract":"This paper considers potential sources of error when using the Ffowcs Williams-Hawkings equation to make predictions of airframe noise, which entails a relatively low-speed, uniform incoming flow encountering geometry of varying complexity. Numerical simulations are used to investigate several model problems where Ffowcs Williams-Hawkings integration surfaces are placed on solid surfaces as well as in the flow. Comparisons with the pressure obtained directly from the simulations reveal that when solid surfaces are used, the acoustic calculations can produce erroneous results in upstream directions and when scattering bodies block the line of sight from observers to the source. Using solid surface input data implies ignoring all volumetric source effects, which include noise generation as well as flow effects. Nonuniform flow alone, such as is found in a steady boundary layer, was not found to be a significant source of error, so the amplitude and phase changes induced by turbulent eddies in massively separated flow regions is speculated to be the primary cause of the error.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"476 - 500"},"PeriodicalIF":1.0,"publicationDate":"2022-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46897284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-01DOI: 10.1177/1475472X221107372
M. Roger, Daniel Acevedo-Giraldo, Marc C. Jacob
The present work addresses the combined aerodynamic and acoustic installation effects observed as a subsonic propeller is partly crossing the near-wake of a wing. Only the tonal noise at multiples of the blade passing frequency is considered. The aerodynamic effect is the onset of additional sound sources caused by blade-wake interaction, compared to the case of the isolated propeller. The acoustic effect is the scattering by the wing. The work is aimed at demonstrating the ability of analytical models to estimate separately these effects, which is of primary interest for the preliminary design steps of a system. A basic experiment carried out in an anechoic, open-jet facility, is described, for validation purposes. The far-field sound measurements are compared to the predictions and some key outcomes are presented. In particular, the model provides guidelines to avoid configurations of excessive noise.
{"title":"Acoustic versus aerodynamic installation effects on a generic propeller-driven flying architecture","authors":"M. Roger, Daniel Acevedo-Giraldo, Marc C. Jacob","doi":"10.1177/1475472X221107372","DOIUrl":"https://doi.org/10.1177/1475472X221107372","url":null,"abstract":"The present work addresses the combined aerodynamic and acoustic installation effects observed as a subsonic propeller is partly crossing the near-wake of a wing. Only the tonal noise at multiples of the blade passing frequency is considered. The aerodynamic effect is the onset of additional sound sources caused by blade-wake interaction, compared to the case of the isolated propeller. The acoustic effect is the scattering by the wing. The work is aimed at demonstrating the ability of analytical models to estimate separately these effects, which is of primary interest for the preliminary design steps of a system. A basic experiment carried out in an anechoic, open-jet facility, is described, for validation purposes. The far-field sound measurements are compared to the predictions and some key outcomes are presented. In particular, the model provides guidelines to avoid configurations of excessive noise.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"585 - 609"},"PeriodicalIF":1.0,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44887360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-28DOI: 10.1177/1475472X221107377
Eric Greenwood, K. Brentner, Robert F. Rau, Ze Feng Ted Gan
A new class of electric aircraft is being developed to transport people and goods as a part of the urban and regional transportation infrastructure. To gain public acceptance of these operations, these aircraft need to be much quieter than conventional airplanes and helicopters. This article seeks to review and summarize the aeroacoustic research relevant to this new category of aircraft. First, a brief review of the history of electric aircraft is provided, with an emphasis on how these aircraft differ from conventional aircraft. Next, the physics of rotor noise generation are reviewed, and the noise sources most likely to be of concern for electric aircraft are highlighted. These are divided into deterministic and nondeterministic sources of noise. Deterministic noise is expected to be dominated by the unsteady loading noise caused by the aerodynamic interactions between components. Nondeterministic noise will be generated by the interaction of the rotor or propeller blades with turbulence from ingested wakes, the atmosphere, and self-generated in the boundary layer. The literature for these noise sources is reviewed with a focus on applicability to electric aircraft. Challenges faced by the aeroacoustician in understanding the noise generation of electric aircraft are then identified, as well as the new opportunities for the prediction and reduction of electric aircraft noise that may be enabled by advances in computational aeroacoustics, flight simulation, and autonomy.
{"title":"Challenges and opportunities for low noise electric aircraft","authors":"Eric Greenwood, K. Brentner, Robert F. Rau, Ze Feng Ted Gan","doi":"10.1177/1475472X221107377","DOIUrl":"https://doi.org/10.1177/1475472X221107377","url":null,"abstract":"A new class of electric aircraft is being developed to transport people and goods as a part of the urban and regional transportation infrastructure. To gain public acceptance of these operations, these aircraft need to be much quieter than conventional airplanes and helicopters. This article seeks to review and summarize the aeroacoustic research relevant to this new category of aircraft. First, a brief review of the history of electric aircraft is provided, with an emphasis on how these aircraft differ from conventional aircraft. Next, the physics of rotor noise generation are reviewed, and the noise sources most likely to be of concern for electric aircraft are highlighted. These are divided into deterministic and nondeterministic sources of noise. Deterministic noise is expected to be dominated by the unsteady loading noise caused by the aerodynamic interactions between components. Nondeterministic noise will be generated by the interaction of the rotor or propeller blades with turbulence from ingested wakes, the atmosphere, and self-generated in the boundary layer. The literature for these noise sources is reviewed with a focus on applicability to electric aircraft. Challenges faced by the aeroacoustician in understanding the noise generation of electric aircraft are then identified, as well as the new opportunities for the prediction and reduction of electric aircraft noise that may be enabled by advances in computational aeroacoustics, flight simulation, and autonomy.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"315 - 381"},"PeriodicalIF":1.0,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45939270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-23DOI: 10.1177/1475472X221107359
Chitrarth Prasad, S. Hromisin, P. Morris
Noise source imaging based on phased array measurements is an essential tool in the aeroacoustic analysis of new nozzle designs, especially at full-scale. This investigation aims to assess the capability of a deconvolution-based beamforming technique to accurately estimate the changes in noise sources for model-scale heated military jets when fluid inserts are used for noise control. This goal is achieved by performing well-validated Large Eddy Simulations (LES) to complement the experimental measurements. The LES data is segregated into its hydrodynamic, acoustic and thermal components using Doak’s Momentum Potential Theory (MPT). The near-field MPT-derived components are subjected to Spectral Proper Orthogonal Decomposition (SPOD) to compare with the frequency-dependent noise source maps obtained directly from experiments. It is shown that fluid inserts alter the naturally occurring Kelvin-Helmholtz (K-H) instability in the jet shear layer, which leads to a change in the directivity of the noise radiated in the near-field. The upstream shift in the noise source distribution resulting from the modified K-H instability is accurately captured by the deconvolution-based source imaging technique using just the far-field measurements. These changes in source locations as a function of frequency are documented.
{"title":"Leveraging large eddy simulations to assess noise source imaging of a controlled supersonic jet","authors":"Chitrarth Prasad, S. Hromisin, P. Morris","doi":"10.1177/1475472X221107359","DOIUrl":"https://doi.org/10.1177/1475472X221107359","url":null,"abstract":"Noise source imaging based on phased array measurements is an essential tool in the aeroacoustic analysis of new nozzle designs, especially at full-scale. This investigation aims to assess the capability of a deconvolution-based beamforming technique to accurately estimate the changes in noise sources for model-scale heated military jets when fluid inserts are used for noise control. This goal is achieved by performing well-validated Large Eddy Simulations (LES) to complement the experimental measurements. The LES data is segregated into its hydrodynamic, acoustic and thermal components using Doak’s Momentum Potential Theory (MPT). The near-field MPT-derived components are subjected to Spectral Proper Orthogonal Decomposition (SPOD) to compare with the frequency-dependent noise source maps obtained directly from experiments. It is shown that fluid inserts alter the naturally occurring Kelvin-Helmholtz (K-H) instability in the jet shear layer, which leads to a change in the directivity of the noise radiated in the near-field. The upstream shift in the noise source distribution resulting from the modified K-H instability is accurately captured by the deconvolution-based source imaging technique using just the far-field measurements. These changes in source locations as a function of frequency are documented.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":"21 1","pages":"438 - 456"},"PeriodicalIF":1.0,"publicationDate":"2022-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45856128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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