Peng Zhao, Yuebing Wang, Yanqi Wu, Xiaoye Hu, Hong Shen, Shiqi Tong, Jie Tao
High intensity of focused ultrasound (HIFU) is an effective tumor therapy, taking advantage of the thermal effect and cavitation effect to generate thermal damage to the target tissue. However, inaccurate ultrasonic dose control may result in ineffective or excessive treatment. Thus, real-time monitoring of the thermal damage formation process is critical. To evaluate the effectiveness of real-time monitoring of B-ultrasound, ex-vivo bovine livers were irradiated by 1.155 MHz focused ultrasound with emission time T1 of 200 ms and interval time T2 of 200 ms. For orthogonal experiments, ultrasound was irradiated at sound power of 100 W, 125 W, and 150 W for 10 s, 20 s, and 40 s, respectively. B-ultrasound image sequences are collected using a 7.5 MHz linear array and compared with backscattered echo signals and thermal damage slices, respectively, to build relationships between B-mode ultrasound monitoring and thermal effect or cavitation effect. The experimental results demonstrated that the tissue ablation process caused by thermal effect cannot be effectively monitored using B-ultrasound, but the process caused by the cavitation effect can. The analysis revealed a strong temporal correlation between the appearance of bright spots in B-ultrasound images and the sudden increase of the scattered echo power spectrum, which were caused by a large number of micro-bubbles from cavitation. The damaged cavity structure of the slices and the development trend of micro-bubbles showed a strong spatial correlation. Furthermore, the sudden increase in the scattered echo signal shows the potential of early warning of cavitation, as it is 1.2–2.0 s ahead of the bright spot in the B-ultrasound image, laying the experimental basis for improving the effectiveness of B-ultrasound monitoring in clinical HIFU surgery.
{"title":"Formation process of thermal damage in a target area of high intensity focused ultrasound and effectiveness analysis of B-ultrasound real-time monitoring","authors":"Peng Zhao, Yuebing Wang, Yanqi Wu, Xiaoye Hu, Hong Shen, Shiqi Tong, Jie Tao","doi":"10.1051/aacus/2022036","DOIUrl":"https://doi.org/10.1051/aacus/2022036","url":null,"abstract":"High intensity of focused ultrasound (HIFU) is an effective tumor therapy, taking advantage of the thermal effect and cavitation effect to generate thermal damage to the target tissue. However, inaccurate ultrasonic dose control may result in ineffective or excessive treatment. Thus, real-time monitoring of the thermal damage formation process is critical. To evaluate the effectiveness of real-time monitoring of B-ultrasound, ex-vivo bovine livers were irradiated by 1.155 MHz focused ultrasound with emission time T1 of 200 ms and interval time T2 of 200 ms. For orthogonal experiments, ultrasound was irradiated at sound power of 100 W, 125 W, and 150 W for 10 s, 20 s, and 40 s, respectively. B-ultrasound image sequences are collected using a 7.5 MHz linear array and compared with backscattered echo signals and thermal damage slices, respectively, to build relationships between B-mode ultrasound monitoring and thermal effect or cavitation effect. The experimental results demonstrated that the tissue ablation process caused by thermal effect cannot be effectively monitored using B-ultrasound, but the process caused by the cavitation effect can. The analysis revealed a strong temporal correlation between the appearance of bright spots in B-ultrasound images and the sudden increase of the scattered echo power spectrum, which were caused by a large number of micro-bubbles from cavitation. The damaged cavity structure of the slices and the development trend of micro-bubbles showed a strong spatial correlation. Furthermore, the sudden increase in the scattered echo signal shows the potential of early warning of cavitation, as it is 1.2–2.0 s ahead of the bright spot in the B-ultrasound image, laying the experimental basis for improving the effectiveness of B-ultrasound monitoring in clinical HIFU surgery.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"45 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90411275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a mobile apparatus for audio-visual experiments (MASAVE) that is easy to build with a low budget and which can run listening tests, pupillometry, and eye-tracking, e.g., for measuring listening effort and fatigue. The design goal was to keep the MASAVE at affordable costs and to enable shipping the preassembled system to the subjects for self-setup in home environments. Two experiments were conducted to validate the proposed system. In the first experiment we tested the reliability of speech perception data gathered using the MASAVE in a less controlled, rather noisy environment. Speech recognition thresholds (SRTs) were measured in a lobby versus a sound-attenuated boot. Results show that the data from both sites did not differ significantly and SRT measurements were possible even for speech levels as low as 40–45 dB SPL. The second experiment validated the usability of the preassembled system and the use of pupillometry measurements under conditions of darkness, which can be achieved by applying a textile cover over the MASAVE and the subject to block out light. The results suggest that the tested participants had no usability issues with setting up the system, that the temperature under the cover increased by several degrees only when the measurement duration was rather long, and that pupillometry measurements can be made with the proposed setup. Overall, the validations indicate that the MASAVE can serve as an alternative when lab testing is not possible, and to gather more data or to reach subject groups that are otherwise difficult to reach.
我们提出了一种用于视听实验的移动设备(MASAVE)，它易于构建，预算低，可以进行听力测试，瞳孔测量和眼球追踪，例如，用于测量听力努力和疲劳。设计目标是使MASAVE保持在可承受的成本，并能够将预组装的系统运送到家庭环境中进行自我设置。进行了两个实验来验证所提出的系统。在第一个实验中，我们测试了使用MASAVE在一个较少控制、相当嘈杂的环境中收集的语音感知数据的可靠性。语音识别阈值(srt)是在大厅和声音衰减的靴子中测量的。结果表明，两个站点的数据没有显著差异，即使语音水平低至40-45 dB SPL, SRT测量也是可能的。第二个实验验证了预组装系统的可用性，并在黑暗条件下使用瞳孔测量法进行测量，这可以通过在MASAVE和受试者上应用纺织品覆盖物来遮挡光线来实现。结果表明，测试参与者在设置系统时没有可用性问题，只有当测量持续时间相当长时，盖下的温度才会增加几度，并且可以使用建议的设置进行瞳孔测量。总的来说，验证表明，MASAVE可以作为一种替代，当实验室测试是不可能的，并收集更多的数据或达到受试者群体，否则难以达到。
{"title":"MASAVE: A mobile test system for audio-visual experiments at home","authors":"Ewald Strasser, T. Brand, J. Rennies","doi":"10.1051/aacus/2022049","DOIUrl":"https://doi.org/10.1051/aacus/2022049","url":null,"abstract":"We present a mobile apparatus for audio-visual experiments (MASAVE) that is easy to build with a low budget and which can run listening tests, pupillometry, and eye-tracking, e.g., for measuring listening effort and fatigue. The design goal was to keep the MASAVE at affordable costs and to enable shipping the preassembled system to the subjects for self-setup in home environments. Two experiments were conducted to validate the proposed system. In the first experiment we tested the reliability of speech perception data gathered using the MASAVE in a less controlled, rather noisy environment. Speech recognition thresholds (SRTs) were measured in a lobby versus a sound-attenuated boot. Results show that the data from both sites did not differ significantly and SRT measurements were possible even for speech levels as low as 40–45 dB SPL. The second experiment validated the usability of the preassembled system and the use of pupillometry measurements under conditions of darkness, which can be achieved by applying a textile cover over the MASAVE and the subject to block out light. The results suggest that the tested participants had no usability issues with setting up the system, that the temperature under the cover increased by several degrees only when the measurement duration was rather long, and that pupillometry measurements can be made with the proposed setup. Overall, the validations indicate that the MASAVE can serve as an alternative when lab testing is not possible, and to gather more data or to reach subject groups that are otherwise difficult to reach.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"4 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76961309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Guanjun Yin, Pan Li, Xuebing Yang, Ye Tian, J. Han, W. Ren, Jianzhong Guo
The characteristics and mechanism of coupling effects between parallel cladded acoustic waveguides (PCAWs) are essential when considering their applications in acoustic wave control and signal processing. We investigated its characteristics and revealed the nature of the coupling effect using a theoretical model of two-dimensional PCAWs and simulation experiments. We derived the eigenmode equation describing the behavior of a single waveguide based on the wave acoustic theory and derived analytic expressions for the coupling effects in the PCAWs using the coupled mode theory. Using the finite-element method, we analyzed the waveguide coupling exhibited by this structure given different configurational and acoustic parameter settings. Both theoretical and simulated results indicate that the input wave directed into one of four ports of this structure propagates and tunnels alternately between the two waveguides. Our theoretical model established yields analytic relations between the coupling lengths as well as the dependence on parameters of the evanescent wave and the structure. Analyses indicate wave coupling in the two PCAWs is essentially mediated by the evanescent wave. The unique evolution of the acoustic wave in PCAWs can be employed to develop pure acoustic devices such as frequency-selective filters, directional couplers, and acoustic switches.
{"title":"Characteristics and mechanism of coupling effects in parallel-cladded acoustic waveguides","authors":"Guanjun Yin, Pan Li, Xuebing Yang, Ye Tian, J. Han, W. Ren, Jianzhong Guo","doi":"10.1051/aacus/2022002","DOIUrl":"https://doi.org/10.1051/aacus/2022002","url":null,"abstract":"The characteristics and mechanism of coupling effects between parallel cladded acoustic waveguides (PCAWs) are essential when considering their applications in acoustic wave control and signal processing. We investigated its characteristics and revealed the nature of the coupling effect using a theoretical model of two-dimensional PCAWs and simulation experiments. We derived the eigenmode equation describing the behavior of a single waveguide based on the wave acoustic theory and derived analytic expressions for the coupling effects in the PCAWs using the coupled mode theory. Using the finite-element method, we analyzed the waveguide coupling exhibited by this structure given different configurational and acoustic parameter settings. Both theoretical and simulated results indicate that the input wave directed into one of four ports of this structure propagates and tunnels alternately between the two waveguides. Our theoretical model established yields analytic relations between the coupling lengths as well as the dependence on parameters of the evanescent wave and the structure. Analyses indicate wave coupling in the two PCAWs is essentially mediated by the evanescent wave. The unique evolution of the acoustic wave in PCAWs can be employed to develop pure acoustic devices such as frequency-selective filters, directional couplers, and acoustic switches.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"16 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88229848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hamid Salarvand, A. Shateri, A. A. Nadooshan, I. Karimipour
Combustion instability caused by the amplification of sound waves is called acoustic or high-frequency instability, which can cause severe damage to the system. Adding baffles is one of the methods of passive instability control. Depending on the geometry of the chamber and the type of application, different baffles are used. In this research, the effect of the longitudinal corrugated baffle on the acoustic characteristics of the combustion chamber is investigated numerically. The quality of each baffle configuration is determined by examining their influence on the essential parameters such as natural frequency shift and damping factor. Modal and harmonic analyses for the acoustic field are conducted to investigate the effect of baffles installed in the combustion chamber. According to the obtained results, the addition of baffle shifts resonant frequencies. In other words, a combustor with baffles is more effective in controlling the instabilities than that without baffles. In addition, it increases the damping factor in the first–second circumferential (tangential) modes, making the system more stable. Also, a quantitative assessment of the acoustics by adding baffles shows that combustion chamber finds a better condition from stability point of view, and the bandwidth increase affects the combustion stability.
{"title":"Numerical study of the effect of the corrugated baffle on the acoustic characteristics of the combustion chamber","authors":"Hamid Salarvand, A. Shateri, A. A. Nadooshan, I. Karimipour","doi":"10.1051/aacus/2022031","DOIUrl":"https://doi.org/10.1051/aacus/2022031","url":null,"abstract":"Combustion instability caused by the amplification of sound waves is called acoustic or high-frequency instability, which can cause severe damage to the system. Adding baffles is one of the methods of passive instability control. Depending on the geometry of the chamber and the type of application, different baffles are used. In this research, the effect of the longitudinal corrugated baffle on the acoustic characteristics of the combustion chamber is investigated numerically. The quality of each baffle configuration is determined by examining their influence on the essential parameters such as natural frequency shift and damping factor. Modal and harmonic analyses for the acoustic field are conducted to investigate the effect of baffles installed in the combustion chamber. According to the obtained results, the addition of baffle shifts resonant frequencies. In other words, a combustor with baffles is more effective in controlling the instabilities than that without baffles. In addition, it increases the damping factor in the first–second circumferential (tangential) modes, making the system more stable. Also, a quantitative assessment of the acoustics by adding baffles shows that combustion chamber finds a better condition from stability point of view, and the bandwidth increase affects the combustion stability.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"8 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76162879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Chehami, Jingfei Liu, P. Pomarède, P. Lohmuller, Boris Pittrowski, F. Meraghni, N. Declercq
Due to the specific elastic properties such as high stiffness to mass ratio, regular microstructure materials are widely used in the industry. The need for nondestructive evaluation is ubiquitous to ensure material quality. As an effective nondestructive testing method, ultrasound has great potential in providing an efficient materials characterization. However, contrary to more convenient ultrasound applications, challenges arise when applying ultrasound to 3D bi-material structures due to the coexistence of different phenomena, including diffraction effects caused by the periodicity. Two linear ultrasound methods, namely the Bragg diffraction and the comb filtering effect, are proposed to address this hurdle. The results show that the comb filtering effect effectively characterizes, respectively, the vertical structural quality of the bi-material. Bragg diffraction can also expose structural variations in the horizontal plane.
{"title":"Ultrasonic investigation of the effect of compressive strains on 3D periodic bi-material structures","authors":"L. Chehami, Jingfei Liu, P. Pomarède, P. Lohmuller, Boris Pittrowski, F. Meraghni, N. Declercq","doi":"10.1051/aacus/2022023","DOIUrl":"https://doi.org/10.1051/aacus/2022023","url":null,"abstract":"Due to the specific elastic properties such as high stiffness to mass ratio, regular microstructure materials are widely used in the industry. The need for nondestructive evaluation is ubiquitous to ensure material quality. As an effective nondestructive testing method, ultrasound has great potential in providing an efficient materials characterization. However, contrary to more convenient ultrasound applications, challenges arise when applying ultrasound to 3D bi-material structures due to the coexistence of different phenomena, including diffraction effects caused by the periodicity. Two linear ultrasound methods, namely the Bragg diffraction and the comb filtering effect, are proposed to address this hurdle. The results show that the comb filtering effect effectively characterizes, respectively, the vertical structural quality of the bi-material. Bragg diffraction can also expose structural variations in the horizontal plane.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"1118 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76780500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The purpose of this investigation is to propose an alternative indoor sound spectrum based on objective and verifiable data, representative for an average household in Europe. It is obtained from the energetic sum of the emission spectra of sound sources commonly found in residential buildings, each weighted by its estimated occurrence time. Such a spectrum could then be used to evaluate airborne sound transmission performance.
{"title":"Towards an alternative representation of indoor acoustic environment","authors":"S. Bailhache, J. Maillard, C. Guigou-Carter","doi":"10.1051/aacus/2022045","DOIUrl":"https://doi.org/10.1051/aacus/2022045","url":null,"abstract":"The purpose of this investigation is to propose an alternative indoor sound spectrum based on objective and verifiable data, representative for an average household in Europe. It is obtained from the energetic sum of the emission spectra of sound sources commonly found in residential buildings, each weighted by its estimated occurrence time. Such a spectrum could then be used to evaluate airborne sound transmission performance.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"8 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78906724","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the brass instrument family, the sound can be modified or attenuated using a mute, which is usually inserted in the bell of the instrument. The objective of this paper is to study the principle and the technological feasibility of an active mute using loudspeakers placed in front or around the instrument bell. This mute must reduce the acoustic power emitted by the instrument while avoiding any impact on its playability. At this stage, an optimal control is considered and no real-time controller is implemented. Results show that an active control placed outside the trombone is theoretically feasible and can be efficient to reduce the acoustic power up to 2000 Hz by placing a ring of sources around the bell and a source in front of the trombone. The instrument input impedance is very slightly affected by the control. In accordance with numerical simulations, the experiment showed that placing a control speaker very close in front of the bell of the instrument modifies the pressure field of the instrument in such a way that it allows to obtain a power attenuation greater than the predicted one. The control is technologically achievable but requires a high power for the closest source.
{"title":"Study of the optimal active control of a trombone","authors":"C. Cavaillès, B. Gazengel, M. Melon, C. Ayrault","doi":"10.1051/aacus/2022015","DOIUrl":"https://doi.org/10.1051/aacus/2022015","url":null,"abstract":"In the brass instrument family, the sound can be modified or attenuated using a mute, which is usually inserted in the bell of the instrument. The objective of this paper is to study the principle and the technological feasibility of an active mute using loudspeakers placed in front or around the instrument bell. This mute must reduce the acoustic power emitted by the instrument while avoiding any impact on its playability. At this stage, an optimal control is considered and no real-time controller is implemented. Results show that an active control placed outside the trombone is theoretically feasible and can be efficient to reduce the acoustic power up to 2000 Hz by placing a ring of sources around the bell and a source in front of the trombone. The instrument input impedance is very slightly affected by the control. In accordance with numerical simulations, the experiment showed that placing a control speaker very close in front of the bell of the instrument modifies the pressure field of the instrument in such a way that it allows to obtain a power attenuation greater than the predicted one. The control is technologically achievable but requires a high power for the closest source.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"2 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88225043","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Clemens Freidhager, S. Schoder, Paul Maurerlehner, Andreas Renz, S. Becker, M. Kaltenbacher
We analyze the differences between the Ffowcs–Williams and Hawking’s approach and a new sound propagation approach based on the finite element method used for solving Lighthill’s aeroacoustic wave equation for compressible flows. In addition, we discuss the applicability of both methods. The sound propagation approach based on Lighthill’s equation introduces a flow-interface boundary condition, similar to permeable boundaries in the Ffowcs–Williams and Hawking’s analogy, which allows the omission of complex geometries in propagation domains. This enables to reduce numeric effort and storage requirements. Thereby, the hybrid aeroacoustic workflow is considered, for which aeroacoustic source terms are computed to couple a flow and a separated acoustic propagation simulation. We present an extensive investigation of Lighthill’s source terms in the sense of the proposed weak formulation of Lighthill’s equation. For validation, measurements from a cold gas test rig are used. In addition, the possibilities of applying both sound propagation methods for investigating the influence of resonators and sound absorbers are discussed.
{"title":"Applicability of two hybrid sound prediction methods for assessing in-duct sound absorbers of turbocharger compressors","authors":"Clemens Freidhager, S. Schoder, Paul Maurerlehner, Andreas Renz, S. Becker, M. Kaltenbacher","doi":"10.1051/aacus/2022025","DOIUrl":"https://doi.org/10.1051/aacus/2022025","url":null,"abstract":"We analyze the differences between the Ffowcs–Williams and Hawking’s approach and a new sound propagation approach based on the finite element method used for solving Lighthill’s aeroacoustic wave equation for compressible flows. In addition, we discuss the applicability of both methods. The sound propagation approach based on Lighthill’s equation introduces a flow-interface boundary condition, similar to permeable boundaries in the Ffowcs–Williams and Hawking’s analogy, which allows the omission of complex geometries in propagation domains. This enables to reduce numeric effort and storage requirements. Thereby, the hybrid aeroacoustic workflow is considered, for which aeroacoustic source terms are computed to couple a flow and a separated acoustic propagation simulation. We present an extensive investigation of Lighthill’s source terms in the sense of the proposed weak formulation of Lighthill’s equation. For validation, measurements from a cold gas test rig are used. In addition, the possibilities of applying both sound propagation methods for investigating the influence of resonators and sound absorbers are discussed.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"34 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89776835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Christof Ocker, F. Czwielong, P. Chaitanya, W. Pannert, S. Becker
A detailed experimental analysis of the aerodynamic and aeroacoustic properties of flat-plate axial fans with slitted leading edges is performed. The sound emissions of five slitted leading edge designs are measured at a constant rotational speed and at a constant total-to-static pressure rise of the fans. For both cases, the fan blades with slitted leading edges reduce the turbulence interaction noise and lead to a reduction of the overall sound pressure level for volume flow rates above 0.6 m3 s−1 compared to an axial fan with solid leading edges. The far-field noise analysis shows that the slits result in a noise reduction for frequencies below 2 kHz and a noise increase above 2 kHz. In addition, sound source localization is conducted with a microphone array and rotating beamforming methods are applied. The identified sound source distributions prove that slitted leading edges reduce turbulence interaction noise, but generate broadband noise in the fan blades’ trailing edge regions. The maximum sound reduction due to the slits could be detected at a dimensionless frequency of $ fh/bar{w}approx 0.5$, where f is the frequency, h is the height of the slit and $ bar{w}$ is the mean relative inflow velocity. The noise reduction mechanism on axial fan blades corresponds well to previous investigations on flat-plate airfoils with slits.
{"title":"Aerodynamic and aeroacoustic properties of axial fan blades with slitted leading edges","authors":"Christof Ocker, F. Czwielong, P. Chaitanya, W. Pannert, S. Becker","doi":"10.1051/aacus/2022043","DOIUrl":"https://doi.org/10.1051/aacus/2022043","url":null,"abstract":"A detailed experimental analysis of the aerodynamic and aeroacoustic properties of flat-plate axial fans with slitted leading edges is performed. The sound emissions of five slitted leading edge designs are measured at a constant rotational speed and at a constant total-to-static pressure rise of the fans. For both cases, the fan blades with slitted leading edges reduce the turbulence interaction noise and lead to a reduction of the overall sound pressure level for volume flow rates above 0.6 m3 s−1 compared to an axial fan with solid leading edges. The far-field noise analysis shows that the slits result in a noise reduction for frequencies below 2 kHz and a noise increase above 2 kHz. In addition, sound source localization is conducted with a microphone array and rotating beamforming methods are applied. The identified sound source distributions prove that slitted leading edges reduce turbulence interaction noise, but generate broadband noise in the fan blades’ trailing edge regions. The maximum sound reduction due to the slits could be detected at a dimensionless frequency of $ fh/bar{w}approx 0.5$, where f is the frequency, h is the height of the slit and $ bar{w}$ is the mean relative inflow velocity. The noise reduction mechanism on axial fan blades corresponds well to previous investigations on flat-plate airfoils with slits.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"36 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81190862","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, the acoustic pressure generated in the near field of a single stream cold jet is investigated. The analysis is focused on the effect of the initial conditions at the nozzle exit parametrized by considering two different turbulence levels and two different boundary layer thicknesses. The study has been performed by processing a numerical database obtained by large-eddy simulations (LES) of a jet flow at M = 0.9 and Re = 105. Pressure time series are obtained from pointwise virtual probes located in several radial and axial positions in the jet near-field. The acoustic pressure is extracted by the application of a consolidated wavelet-based procedure and the achieved acoustic signals are analyzed in terms of global quantities as well as by computing wavelet-reconstructed Fourier spectra. The results show that both the boundary-layer thickness and the turbulence level significantly affect the acoustic pressure in terms of its intensity and directivity whereas the distribution of energy in the frequency domain depends appreciably, only on the boundary-layer thickness.
{"title":"On the influence of the nozzle exhaust initial conditions on the near field acoustic pressure","authors":"R. Camussi, S. Meloni, C. Bogey","doi":"10.1051/aacus/2022051","DOIUrl":"https://doi.org/10.1051/aacus/2022051","url":null,"abstract":"In this paper, the acoustic pressure generated in the near field of a single stream cold jet is investigated. The analysis is focused on the effect of the initial conditions at the nozzle exit parametrized by considering two different turbulence levels and two different boundary layer thicknesses. The study has been performed by processing a numerical database obtained by large-eddy simulations (LES) of a jet flow at M = 0.9 and Re = 105. Pressure time series are obtained from pointwise virtual probes located in several radial and axial positions in the jet near-field. The acoustic pressure is extracted by the application of a consolidated wavelet-based procedure and the achieved acoustic signals are analyzed in terms of global quantities as well as by computing wavelet-reconstructed Fourier spectra. The results show that both the boundary-layer thickness and the turbulence level significantly affect the acoustic pressure in terms of its intensity and directivity whereas the distribution of energy in the frequency domain depends appreciably, only on the boundary-layer thickness.","PeriodicalId":48486,"journal":{"name":"Acta Acustica","volume":"12 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83472583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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