Pub Date : 2022-11-01DOI: 10.1177/1475472X221136884
Sai Manikanta Kaja, Srinath Srinivasan, S. Chaitanya, Krishnamurthy Srinivasan
This study uses specialized deep neural networks comprising dense and convolutional neural networks to localize noise sources and reconstruct acoustic data on a reconstruction plane. The networks are trained on simulated acoustic data free from any form of noise in the signal. It is observed that neural networks can effectively localize monopole and dipole sources and reconstruct the acoustic data in reconstruction planes with higher accuracy than conventional methods. Performance of the networks is consistent over changes in some parameters like the source strength, noise in the input signal, and frequency range. Various tests are performed to assess the individual network performance. Results indicate that neural networks trained on a subset of the data are effective over the entire data set without significant bias or variance. Errors as low as 1% are observed, and the maximum error observed is below 5%. While reconstruction error decreased with an increase in the frequency of monopole sources, it increased with an increase in frequency for dipole sources.
{"title":"Data-driven neural networks for source localization and reconstruction using a planar array","authors":"Sai Manikanta Kaja, Srinath Srinivasan, S. Chaitanya, Krishnamurthy Srinivasan","doi":"10.1177/1475472X221136884","DOIUrl":"https://doi.org/10.1177/1475472X221136884","url":null,"abstract":"This study uses specialized deep neural networks comprising dense and convolutional neural networks to localize noise sources and reconstruct acoustic data on a reconstruction plane. The networks are trained on simulated acoustic data free from any form of noise in the signal. It is observed that neural networks can effectively localize monopole and dipole sources and reconstruct the acoustic data in reconstruction planes with higher accuracy than conventional methods. Performance of the networks is consistent over changes in some parameters like the source strength, noise in the input signal, and frequency range. Various tests are performed to assess the individual network performance. Results indicate that neural networks trained on a subset of the data are effective over the entire data set without significant bias or variance. Errors as low as 1% are observed, and the maximum error observed is below 5%. While reconstruction error decreased with an increase in the frequency of monopole sources, it increased with an increase in frequency for dipole sources.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45991707","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 : 2022-11-01DOI: 10.1177/1475472X221136883
T. Yang, Xi Chen, Qi-jun Zhao, Guo-qing Zhao
To study the influence of non-uniform flowfield on the propagation characteristics of helicopter rotor noise, a Hybrid Computational Aeroacoustics (HCAA) method is developed. The acoustic source region is simulated by Computational Fluid Dynamics (CFD) technique with the Unsteady Reynolds Averaged Navier-Stokes equations (URANS) as the governing equations. Acoustic near-field is simulated by Computational Aeroacoustics (CAA) technique with the Linearized Euler Equations (LEE) as the governing equations, and the numerical discretization of the LEE is accomplished by Runge-Kutta Discontinuous Galerkin (RKDG) method. A novel acoustic source extraction method based on pressure and pressure gradient is proposed to accomplish the one-way CFD-CAA weak coupling. The HCAA method is validated through comparisons with noise experimental data of the UH-1H model rotor and the BO-105 model rotor. Based on the proposed HCAA method, the convection and refraction effects of rotor noise under different collective pitch angles are analyzed. The results show that the distortion effect of the rotor noise is most affected by the non-uniformly distributed downwash velocity field, resulting in an increment of acoustic energy below the rotor plane. The effect of non-uniformly distributed downwash velocity on noise propagation increases with the increase of the collective pitch angle. For the UH-1H model rotor, the maximum change of the sound pressure level is 0.8 dB (about 10% change of the effective sound pressure).
{"title":"Numerical study on the noise propagation characteristics of rotor in non-uniform downwash flowfield Based on Linearized Euler Equations","authors":"T. Yang, Xi Chen, Qi-jun Zhao, Guo-qing Zhao","doi":"10.1177/1475472X221136883","DOIUrl":"https://doi.org/10.1177/1475472X221136883","url":null,"abstract":"To study the influence of non-uniform flowfield on the propagation characteristics of helicopter rotor noise, a Hybrid Computational Aeroacoustics (HCAA) method is developed. The acoustic source region is simulated by Computational Fluid Dynamics (CFD) technique with the Unsteady Reynolds Averaged Navier-Stokes equations (URANS) as the governing equations. Acoustic near-field is simulated by Computational Aeroacoustics (CAA) technique with the Linearized Euler Equations (LEE) as the governing equations, and the numerical discretization of the LEE is accomplished by Runge-Kutta Discontinuous Galerkin (RKDG) method. A novel acoustic source extraction method based on pressure and pressure gradient is proposed to accomplish the one-way CFD-CAA weak coupling. The HCAA method is validated through comparisons with noise experimental data of the UH-1H model rotor and the BO-105 model rotor. Based on the proposed HCAA method, the convection and refraction effects of rotor noise under different collective pitch angles are analyzed. The results show that the distortion effect of the rotor noise is most affected by the non-uniformly distributed downwash velocity field, resulting in an increment of acoustic energy below the rotor plane. The effect of non-uniformly distributed downwash velocity on noise propagation increases with the increase of the collective pitch angle. For the UH-1H model rotor, the maximum change of the sound pressure level is 0.8 dB (about 10% change of the effective sound pressure).","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47616424","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 : 2022-11-01DOI: 10.1177/1475472X221140869
Arun Mg, S. Tj
The present study experimentally investigates the aerodynamic noise from the flow around cylinders of square and equilateral triangle cross-sections at different angles of incidence (α). The cylinder models have a side dimension of 10 mm and a span of 300 mm. The free stream velocity (U 0 ) is in the range of 12–36 m/s, and the corresponding Reynolds numbers are 7.8 × 103 to 2.3 × 104, which is in the subcritical flow regime. The characteristic acoustic tones are generated at α = 30° and 45° for square and triangular cylinders. The frequency of acoustic tones linearly increases with the free stream velocity, and the corresponding Strouhal numbers are found to be in the range of 0.13–0.16. Depending on the angle of incidence, the overall sound pressure level is higher than the background noise by 4–24 dB for the square cylinder and 3–15 dB for the triangular cylinder at U 0 = 36 m/s. The highest noise level of the square cylinder is 90 dB at α = 45° and 79 dB at α = 30° for the triangular cylinder. The spectral scaling with the sixth power of the free stream velocity indicates the dipole behaviour of the acoustic tones. The mean and root-mean-square velocity profiles in the wake region characterise the noise emissions at different angles of incidence. The comparative acoustic study of the non-circular cylinders with a circular counterpart showed that the highest noise level is from the square cylinder at α = 45°. The directivity study shows that the noise level of the square cylinder at α = 45° at 90° angular location (θ) is higher by 6.5 dB than that at θ = 30°.
{"title":"Aerodynamic noise characteristics of non-circular cylinders in subcritical flow regime","authors":"Arun Mg, S. Tj","doi":"10.1177/1475472X221140869","DOIUrl":"https://doi.org/10.1177/1475472X221140869","url":null,"abstract":"The present study experimentally investigates the aerodynamic noise from the flow around cylinders of square and equilateral triangle cross-sections at different angles of incidence (α). The cylinder models have a side dimension of 10 mm and a span of 300 mm. The free stream velocity (U 0 ) is in the range of 12–36 m/s, and the corresponding Reynolds numbers are 7.8 × 103 to 2.3 × 104, which is in the subcritical flow regime. The characteristic acoustic tones are generated at α = 30° and 45° for square and triangular cylinders. The frequency of acoustic tones linearly increases with the free stream velocity, and the corresponding Strouhal numbers are found to be in the range of 0.13–0.16. Depending on the angle of incidence, the overall sound pressure level is higher than the background noise by 4–24 dB for the square cylinder and 3–15 dB for the triangular cylinder at U 0 = 36 m/s. The highest noise level of the square cylinder is 90 dB at α = 45° and 79 dB at α = 30° for the triangular cylinder. The spectral scaling with the sixth power of the free stream velocity indicates the dipole behaviour of the acoustic tones. The mean and root-mean-square velocity profiles in the wake region characterise the noise emissions at different angles of incidence. The comparative acoustic study of the non-circular cylinders with a circular counterpart showed that the highest noise level is from the square cylinder at α = 45°. The directivity study shows that the noise level of the square cylinder at α = 45° at 90° angular location (θ) is higher by 6.5 dB than that at θ = 30°.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43585679","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 : 2022-11-01DOI: 10.1177/1475472X221136882
S. Redonnet, Thomas G Schmidt
This study concerns the experimental characterization of trailing edge noise, the understanding of which is crucial for mitigating acoustic pollution across major industries. An aeroacoustic experiment is carried out using a closed-vein wind tunnel to investigate the laminar boundary layer vortex-shedding (LBL-VS) noise of a symmetric NACA0021 airfoil in low Reynolds number flows (Re ≤ 163,500). Steady aerodynamic and acoustic measurements are performed, with numerous conditions covered (flow velocity from 10 m/s to 24.5 m/s, airfoil incidence from −10° to 10°). The aerodynamic results reveal that, in the pre-stall regime, the airfoil’ suction side exhibits both a laminar separation bubble (LSB) and a trailing edge detached flow – which both make LBL-VS noise likely to occur. The acoustic results reveal that, when at low speed and moderate incidence, the airfoil emits one to two tones, which can be both attributed to LBL-VS noise. In particular, their respective frequency is seen to scale as the 0.8th power of the flow velocity, whereas varying linearly with the incidence. At higher speeds, these two tones vanish to the profit of other, more intense tonal emissions, whose frequency does not scale with the velocity nor the incidence. These tones are attributed to resonance effects coming from a retroaction of the reverberant environment onto the LBL-VS noise emission, which then locks-on to some of the duct resonant frequencies via an acoustic feedback loop. Revealing indirectly the presence of the pre-existing LBL-VS noise, these resonant tones emerge only when the flow velocity and incidence obey specific conditions, namely a roughly linear relationship.
{"title":"Experimental investigation of the laminar boundary layer vortex-shedding noise by an airfoil within a closed-vein wind tunnel","authors":"S. Redonnet, Thomas G Schmidt","doi":"10.1177/1475472X221136882","DOIUrl":"https://doi.org/10.1177/1475472X221136882","url":null,"abstract":"This study concerns the experimental characterization of trailing edge noise, the understanding of which is crucial for mitigating acoustic pollution across major industries. An aeroacoustic experiment is carried out using a closed-vein wind tunnel to investigate the laminar boundary layer vortex-shedding (LBL-VS) noise of a symmetric NACA0021 airfoil in low Reynolds number flows (Re ≤ 163,500). Steady aerodynamic and acoustic measurements are performed, with numerous conditions covered (flow velocity from 10 m/s to 24.5 m/s, airfoil incidence from −10° to 10°). The aerodynamic results reveal that, in the pre-stall regime, the airfoil’ suction side exhibits both a laminar separation bubble (LSB) and a trailing edge detached flow – which both make LBL-VS noise likely to occur. The acoustic results reveal that, when at low speed and moderate incidence, the airfoil emits one to two tones, which can be both attributed to LBL-VS noise. In particular, their respective frequency is seen to scale as the 0.8th power of the flow velocity, whereas varying linearly with the incidence. At higher speeds, these two tones vanish to the profit of other, more intense tonal emissions, whose frequency does not scale with the velocity nor the incidence. These tones are attributed to resonance effects coming from a retroaction of the reverberant environment onto the LBL-VS noise emission, which then locks-on to some of the duct resonant frequencies via an acoustic feedback loop. Revealing indirectly the presence of the pre-existing LBL-VS noise, these resonant tones emerge only when the flow velocity and incidence obey specific conditions, namely a roughly linear relationship.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47627436","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 : 2022-10-29DOI: 10.1177/1475472X221136885
Chengchun Zhang, Xiaowei Sun, T. Du, Chun Shen, Zheng-wu Chen, Dong Liang, Jiale Zhao, Yingchao Zhang
The cylinder-airfoil interaction noise can be reduced by changing the shape of the leading edge of the downstream airfoil. Generally, this way not only can reduce the interaction noise at middle and high frequency, but also can change the peak noise at the low frequency. This study attempts to affect the cylinder-airfoil interaction noise from the perspective of reducing the intensity of the upstream wake shedding vortex. In order to achieve this target, the equally spaced grooves were cut into the upstream cylinder, and the acoustic wind tunnel tests at various incoming velocities (20–60m·s−1) were conducted to compare the interaction noise of cylinder-airfoil (NACA0012) models. It is found that the grooved structure can effectively reduce the peak noise at characteristic frequencies bellow 1000 Hz and the broadband noise in the mid-frequency ranging from 1000 Hz to 3000 Hz, especially for the higher incoming velocity. Thereinto, the peak noise and overall sound pressure level (OASPL) with the grooved cylinder are reduced by 13 dB and 7.2 dB, respectively at the incoming velocity of 60 m·s−1. The numerical simulations based on the large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) acoustic analogy were performed to further reveal the mechanisms of noise reduction when the velocity is 60 m·s−1. The results show that the vortex shedding from cylinder wake is suppressed by the grooved cylinder and the vortex structure at the leading edge of the airfoil is also cut into the small-scale vortex structures by the grooved structure. The pressure fluctuation amplitude and the peak value turbulent kinetic energy in the wake of the grooved cylinder are significantly reduced. In addition, the further spectrum analysis reveals that the weak correlation of the vortex shedding on the grooved cylinder could lead to the suppression of the pressure fluctuation in the cylinder wake, and thereby the interaction noise is significantly reduced.
{"title":"Reduction of noise generated by cylinder-airfoil interaction using grooved structures on the upstream cylinder","authors":"Chengchun Zhang, Xiaowei Sun, T. Du, Chun Shen, Zheng-wu Chen, Dong Liang, Jiale Zhao, Yingchao Zhang","doi":"10.1177/1475472X221136885","DOIUrl":"https://doi.org/10.1177/1475472X221136885","url":null,"abstract":"The cylinder-airfoil interaction noise can be reduced by changing the shape of the leading edge of the downstream airfoil. Generally, this way not only can reduce the interaction noise at middle and high frequency, but also can change the peak noise at the low frequency. This study attempts to affect the cylinder-airfoil interaction noise from the perspective of reducing the intensity of the upstream wake shedding vortex. In order to achieve this target, the equally spaced grooves were cut into the upstream cylinder, and the acoustic wind tunnel tests at various incoming velocities (20–60m·s−1) were conducted to compare the interaction noise of cylinder-airfoil (NACA0012) models. It is found that the grooved structure can effectively reduce the peak noise at characteristic frequencies bellow 1000 Hz and the broadband noise in the mid-frequency ranging from 1000 Hz to 3000 Hz, especially for the higher incoming velocity. Thereinto, the peak noise and overall sound pressure level (OASPL) with the grooved cylinder are reduced by 13 dB and 7.2 dB, respectively at the incoming velocity of 60 m·s−1. The numerical simulations based on the large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) acoustic analogy were performed to further reveal the mechanisms of noise reduction when the velocity is 60 m·s−1. The results show that the vortex shedding from cylinder wake is suppressed by the grooved cylinder and the vortex structure at the leading edge of the airfoil is also cut into the small-scale vortex structures by the grooved structure. The pressure fluctuation amplitude and the peak value turbulent kinetic energy in the wake of the grooved cylinder are significantly reduced. In addition, the further spectrum analysis reveals that the weak correlation of the vortex shedding on the grooved cylinder could lead to the suppression of the pressure fluctuation in the cylinder wake, and thereby the interaction noise is significantly reduced.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2022-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43587164","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: 10.1177/1475472X221107363
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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
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