Pub Date : 2023-09-30DOI: 10.1177/1475472x231199186
Charles E Tinney, Yingjun Zhao-Dubuc, John Valdez
Proper orthogonal decomposition and the Vold-Kalman order tracking filter are combined to evaluate the most energetic components of the sound field produced by a coaxial, co-rotating rotor in hover. The study leverages the database generated by Tinney and Valdez (2020; AIAA J. vol. 58, no. 4) comprising an array of eight stationary microphones oriented to capture the acoustic near-field below the rotor disk plane where ground observers are expected to reside and where concerns over community annoyance are greatest. Changes to rotor conditions focus primarily on rotor speed and index angle (angular separation between the upper and lower rotors), as this has the greatest effect on the sound field produced by stacked rotors by way of the constructive and destructive interference of the sound generated, separately, by the upper and lower rotors. Proper orthogonal decomposition is performed using a kernel constructed from auto and cross-spectral densities of the spatially coherent sound field. The eigenvectors demonstrate the spatial extent of the sound field for discrete frequencies corresponding to the first few blade pass frequency harmonics. In order to improve the clarity and accuracy of the low-order reconstructions, a second generation, Vold-Kalman multi-order tracking filter is employed to isolate discrete frequencies. Relative to conventional spectral filtering methods, the Vold-Kalman filter is performed in the time-domain and is shown to accurately isolate discrete tones while preserving changes to the phase of the signal. Findings from this analysis reveal the effect of index angle on the spatial make-up of the coherent sound field produced by hovering stacked rotors.
{"title":"The space-time structure of sound produced by stacked rotors in hover using Vold-Kalman filters and proper orthogonal decomposition","authors":"Charles E Tinney, Yingjun Zhao-Dubuc, John Valdez","doi":"10.1177/1475472x231199186","DOIUrl":"https://doi.org/10.1177/1475472x231199186","url":null,"abstract":"Proper orthogonal decomposition and the Vold-Kalman order tracking filter are combined to evaluate the most energetic components of the sound field produced by a coaxial, co-rotating rotor in hover. The study leverages the database generated by Tinney and Valdez (2020; AIAA J. vol. 58, no. 4) comprising an array of eight stationary microphones oriented to capture the acoustic near-field below the rotor disk plane where ground observers are expected to reside and where concerns over community annoyance are greatest. Changes to rotor conditions focus primarily on rotor speed and index angle (angular separation between the upper and lower rotors), as this has the greatest effect on the sound field produced by stacked rotors by way of the constructive and destructive interference of the sound generated, separately, by the upper and lower rotors. Proper orthogonal decomposition is performed using a kernel constructed from auto and cross-spectral densities of the spatially coherent sound field. The eigenvectors demonstrate the spatial extent of the sound field for discrete frequencies corresponding to the first few blade pass frequency harmonics. In order to improve the clarity and accuracy of the low-order reconstructions, a second generation, Vold-Kalman multi-order tracking filter is employed to isolate discrete frequencies. Relative to conventional spectral filtering methods, the Vold-Kalman filter is performed in the time-domain and is shown to accurately isolate discrete tones while preserving changes to the phase of the signal. Findings from this analysis reveal the effect of index angle on the spatial make-up of the coherent sound field produced by hovering stacked rotors.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136280525","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 : 2023-09-30DOI: 10.1177/1475472x231206889
K. Viswanathan
Non-axisymmetric geometries, mainly elliptic and rectangular, have been proposed for the reduction of jet noise vis-à-vis round nozzles. Most of the studies of these nozzles are from unheated jets and are restricted to nozzles of very small size. Furthermore, all of them have been carried out at static conditions, thereby rendering their value to insignificance for practical applications. All engines in service with long ducts and a confluent nozzle incorporate an internal lobed mixer. The aeroacoustic characteristics of an elliptic compound nozzle that represents the geometry of an existing low bypass ratio (BPR) turbofan engine, is investigated at 1/7th scale in this study. Typical engine cycle conditions are chosen; data are acquired statically and in the presence of a flight stream. The aspect ratio of the nozzle is 2.0; higher aspect ratios are not suitable for engine applications. The results are compared with a round compound nozzle with the same internal geometry, so as to assess the acoustic benefit, if any, of the elliptic nozzle. Both a simple internal splitter and an in-service lobed mixer have been considered. The elliptic nozzle introduces azimuthal asymmetry even for an unheated jet; the magnitude of azimuthal variation becomes pronounced for heated jets. Typically, the lowest level of noise is observed towards the narrow side of the elliptic nozzle (ϕ = 0°); the noise level gradually increases and reaches a maximum towards the broader side (ϕ = 90°). Though there are some superficial similarities between the elliptic and beveled nozzles, it is shown that the noise characteristics are very different. A systematic study is carried out, with step-by-step build up to realistic geometry, with forward flight. A large noise reduction of ∼3 to ∼4 EPNdB is observed for the splitter nozzle under static conditions. The introduction of a realistic lobed mixer reduces this benefit to close to zero. Finally, there is a noise increase at all azimuthal angles with forward flight. Therefore, the elliptic nozzle does not provide any EPNL benefit for actual nozzle geometry and consequently does not constitute a viable design for noise reduction. The importance of evaluating noise reduction concepts using appropriate geometry and under realistic forward flight conditions is emphasized once again.
{"title":"Is an elliptic jet quieter than a round jet?","authors":"K. Viswanathan","doi":"10.1177/1475472x231206889","DOIUrl":"https://doi.org/10.1177/1475472x231206889","url":null,"abstract":"Non-axisymmetric geometries, mainly elliptic and rectangular, have been proposed for the reduction of jet noise vis-à-vis round nozzles. Most of the studies of these nozzles are from unheated jets and are restricted to nozzles of very small size. Furthermore, all of them have been carried out at static conditions, thereby rendering their value to insignificance for practical applications. All engines in service with long ducts and a confluent nozzle incorporate an internal lobed mixer. The aeroacoustic characteristics of an elliptic compound nozzle that represents the geometry of an existing low bypass ratio (BPR) turbofan engine, is investigated at 1/7th scale in this study. Typical engine cycle conditions are chosen; data are acquired statically and in the presence of a flight stream. The aspect ratio of the nozzle is 2.0; higher aspect ratios are not suitable for engine applications. The results are compared with a round compound nozzle with the same internal geometry, so as to assess the acoustic benefit, if any, of the elliptic nozzle. Both a simple internal splitter and an in-service lobed mixer have been considered. The elliptic nozzle introduces azimuthal asymmetry even for an unheated jet; the magnitude of azimuthal variation becomes pronounced for heated jets. Typically, the lowest level of noise is observed towards the narrow side of the elliptic nozzle (ϕ = 0°); the noise level gradually increases and reaches a maximum towards the broader side (ϕ = 90°). Though there are some superficial similarities between the elliptic and beveled nozzles, it is shown that the noise characteristics are very different. A systematic study is carried out, with step-by-step build up to realistic geometry, with forward flight. A large noise reduction of ∼3 to ∼4 EPNdB is observed for the splitter nozzle under static conditions. The introduction of a realistic lobed mixer reduces this benefit to close to zero. Finally, there is a noise increase at all azimuthal angles with forward flight. Therefore, the elliptic nozzle does not provide any EPNL benefit for actual nozzle geometry and consequently does not constitute a viable design for noise reduction. The importance of evaluating noise reduction concepts using appropriate geometry and under realistic forward flight conditions is emphasized once again.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136280510","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 : 2023-09-29DOI: 10.1177/1475472x231206497
Ezedin Ayaliew Yimam, Tolga Demircan
This study numerically examined the propellant flow from gunfire using the kω-SST turbulence model and their sound attenuation using the Ffowcs-Williams and Hawkins equations (FW-H). For simulation, a pressure-based solver and 3D axisymmetric geometry were used. The second-order implicit time approach and the second-order upwind scheme spatial discretization were used in the simulation. The maximum exit pressure was 3.748 MPa for the suppressor with a length of 70 mm and diameter of 20 mm. However, when the diameter suppressor increased by 1/6, the maximum exit pressure was reduced to 3.4961 MPa. When the length increased by 1/6, the maximum pressure became 3.3636 MPa. Lastly, when the diameter and length were increased by 1/6, the maximum exit pressure became 3.177 MPa. For this suppressor, 20.835 dB (12.29%) sound pressure level attenuation was achieved with 16.823 MPa (84.115%) overpressure reduction and 484.86 K or 32.32% temperature reduction. Generally, the attenuation increased with the increase in the suppressor’s internal volume.
{"title":"Investigation of the effects of volume change on flow structure and acoustic in a silencer","authors":"Ezedin Ayaliew Yimam, Tolga Demircan","doi":"10.1177/1475472x231206497","DOIUrl":"https://doi.org/10.1177/1475472x231206497","url":null,"abstract":"This study numerically examined the propellant flow from gunfire using the kω-SST turbulence model and their sound attenuation using the Ffowcs-Williams and Hawkins equations (FW-H). For simulation, a pressure-based solver and 3D axisymmetric geometry were used. The second-order implicit time approach and the second-order upwind scheme spatial discretization were used in the simulation. The maximum exit pressure was 3.748 MPa for the suppressor with a length of 70 mm and diameter of 20 mm. However, when the diameter suppressor increased by 1/6, the maximum exit pressure was reduced to 3.4961 MPa. When the length increased by 1/6, the maximum pressure became 3.3636 MPa. Lastly, when the diameter and length were increased by 1/6, the maximum exit pressure became 3.177 MPa. For this suppressor, 20.835 dB (12.29%) sound pressure level attenuation was achieved with 16.823 MPa (84.115%) overpressure reduction and 484.86 K or 32.32% temperature reduction. Generally, the attenuation increased with the increase in the suppressor’s internal volume.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135247749","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 : 2023-09-25DOI: 10.1177/1475472x231199182
Christopher KW Tam, John T Spyropoulos, Allan C Aubert, Russell W Powers
Ffowcs Williams et al were the first to discover crackle in the noise of the Concorde when the Olympus 593 engine which propelled Concorde was operating at afterburner power. Ffowcs Williams et al described crackle as a transient phenomenon. The primary objective of the present investigation is to show that the noise of F-18E aircraft has crackle. The fundamental elements in the noise of a crackling jet described by Ffowcs Williams et al are sawtooth-like pulses, bursts and trains of bursts. All these characteristic features of pressure pulses are identified in the noise of F-18E aircraft. By including a minimum pulse amplitude requirement based on the level found in the noise of the Concorde by Ffowcs Williams et al, a set of sufficiency conditions for the presence of crackle is established. It is found that crackle exists in the noise of an F-18E aircraft over a fairly large angular sector in the downstream direction. In the literature, the existence of sawtooth-like sound pulses in a noise field is often taken as an indicator of the presence of crackle. The importance of pressure pulse waveform on its impact on human hearing is briefly investigated by using a simple mechanical model of the ear.
{"title":"A study of the phenomenon of “crackle” associated with the noise of high-performance aircraft at afterburner","authors":"Christopher KW Tam, John T Spyropoulos, Allan C Aubert, Russell W Powers","doi":"10.1177/1475472x231199182","DOIUrl":"https://doi.org/10.1177/1475472x231199182","url":null,"abstract":"Ffowcs Williams et al were the first to discover crackle in the noise of the Concorde when the Olympus 593 engine which propelled Concorde was operating at afterburner power. Ffowcs Williams et al described crackle as a transient phenomenon. The primary objective of the present investigation is to show that the noise of F-18E aircraft has crackle. The fundamental elements in the noise of a crackling jet described by Ffowcs Williams et al are sawtooth-like pulses, bursts and trains of bursts. All these characteristic features of pressure pulses are identified in the noise of F-18E aircraft. By including a minimum pulse amplitude requirement based on the level found in the noise of the Concorde by Ffowcs Williams et al, a set of sufficiency conditions for the presence of crackle is established. It is found that crackle exists in the noise of an F-18E aircraft over a fairly large angular sector in the downstream direction. In the literature, the existence of sawtooth-like sound pulses in a noise field is often taken as an indicator of the presence of crackle. The importance of pressure pulse waveform on its impact on human hearing is briefly investigated by using a simple mechanical model of the ear.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135859170","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 : 2023-09-15DOI: 10.1177/1475472x231199183
Jayanta Panda, Evan D Crowe, Lester A Langford, Earl T Daley, Kenneth R Hamm, Joel W Sills
A new phased array of microphones, suitable for the harsh environment of a rocket launch, was built and tested during a static firing of an RS-25 engine. It uses 70 piezo-resistive, dynamic pressure sensors, optimally distributed on a 10.5-ft diameter open frame dome structure and has a 200-ft long cable bundle to carry the signals to a weather-protected cabinet containing the data systems. The test stand was imaged using an infra-red camera and a visible wavelength camera, and the beamformed noise maps were superimposed on the photographs. The first-time data from a full-scale engine test stand showed that the plume deflector at the bottom of the engine was the primary noise source. The openings of the test stand around the nozzle exit were also found to be noise sources particularly at higher frequencies. The final goal is to utilize the array during NASA’s Artemis-II launch at Kennedy Space Center.
{"title":"Acoustic sources identified using a microphone phased array during a rocket engine test","authors":"Jayanta Panda, Evan D Crowe, Lester A Langford, Earl T Daley, Kenneth R Hamm, Joel W Sills","doi":"10.1177/1475472x231199183","DOIUrl":"https://doi.org/10.1177/1475472x231199183","url":null,"abstract":"A new phased array of microphones, suitable for the harsh environment of a rocket launch, was built and tested during a static firing of an RS-25 engine. It uses 70 piezo-resistive, dynamic pressure sensors, optimally distributed on a 10.5-ft diameter open frame dome structure and has a 200-ft long cable bundle to carry the signals to a weather-protected cabinet containing the data systems. The test stand was imaged using an infra-red camera and a visible wavelength camera, and the beamformed noise maps were superimposed on the photographs. The first-time data from a full-scale engine test stand showed that the plume deflector at the bottom of the engine was the primary noise source. The openings of the test stand around the nozzle exit were also found to be noise sources particularly at higher frequencies. The final goal is to utilize the array during NASA’s Artemis-II launch at Kennedy Space Center.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135396371","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 : 2023-09-06DOI: 10.1177/1475472x231199188
Aharon Z. Karon, K. K. Ahuja
The Reynolds number and Mach number are classical quantities used to determine the similarity of aerodynamic flows. Existing studies on the role of Reynolds Number on jet noise show inconsistent results, casting doubt on how small a nozzle diameter can be for the classical jet noise scaling laws to hold. A systematic study was therefore undertaken to resolve this issue. The Reynolds number of jet flows was adjusted using a Mach number variation between 0.4 and 0.8, and nozzle-exit diameters of 0.25, 0.5, and two inches. When the jet noise measurements were normalized, spectral collapse was observed for the spectra across the whole Reynolds number range. It was found that the Reynolds number does not have a significant effect on jet noise, and jet noise can be scaled from even the smallest of nozzle to larger nozzles.
{"title":"Reynolds number and jet noise scaling","authors":"Aharon Z. Karon, K. K. Ahuja","doi":"10.1177/1475472x231199188","DOIUrl":"https://doi.org/10.1177/1475472x231199188","url":null,"abstract":"The Reynolds number and Mach number are classical quantities used to determine the similarity of aerodynamic flows. Existing studies on the role of Reynolds Number on jet noise show inconsistent results, casting doubt on how small a nozzle diameter can be for the classical jet noise scaling laws to hold. A systematic study was therefore undertaken to resolve this issue. The Reynolds number of jet flows was adjusted using a Mach number variation between 0.4 and 0.8, and nozzle-exit diameters of 0.25, 0.5, and two inches. When the jet noise measurements were normalized, spectral collapse was observed for the spectra across the whole Reynolds number range. It was found that the Reynolds number does not have a significant effect on jet noise, and jet noise can be scaled from even the smallest of nozzle to larger nozzles.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42997275","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 : 2023-09-06DOI: 10.1177/1475472x231199184
Evren Yenigelen, Philip J Morris
The design of a rocket launch environment is a complex process with many different aspects that are highly interconnected. Acoustics, which is one of these, should be investigated in detail due to possible devastating effects on the launch vehicle, crew, and launch environment. This study uses a numerical method to consider a passive noise reduction method applied to a supersonic jet impinging on an inclined flame deflector to decrease the acoustic loads on the launch vehicle and noise levels in the far-field. In a supersonic jet impinging on an inclined flat plate configuration, acoustic waves that travel upstream originate from the impingement and wall jet regions. These upstream traveling waves are a combination of the acoustic waves that are produced by the high speed jet flows in the wall jet region and acoustic waves that reflect from the impingement wall. Due to the inclination of the impingement plate, these waves either travel to the far-field in the upstream direction or travel towards the free-jet region interacting with the high speed flow near the nozzle lip. This interaction can create a self sustaining feedback loop, which can cause acoustic tones to appear in the near- and far-field spectra. It is the aim of the present study to block the upstream traveling waves by introducing a second inclined wall with a circular cut-out between the nozzle exit and the impingement plate. Different configurations with different wall locations and cut-out sizes are investigated using a Detached Eddy Simulation CFD solver and an acoustic solver that is based on the Ffowcs Williams and Hawkings analogy. The mechanisms for the establishment of the feedback loops are examined.
{"title":"Flow and acoustics in a model rocket flame deflector and deflector cover","authors":"Evren Yenigelen, Philip J Morris","doi":"10.1177/1475472x231199184","DOIUrl":"https://doi.org/10.1177/1475472x231199184","url":null,"abstract":"The design of a rocket launch environment is a complex process with many different aspects that are highly interconnected. Acoustics, which is one of these, should be investigated in detail due to possible devastating effects on the launch vehicle, crew, and launch environment. This study uses a numerical method to consider a passive noise reduction method applied to a supersonic jet impinging on an inclined flame deflector to decrease the acoustic loads on the launch vehicle and noise levels in the far-field. In a supersonic jet impinging on an inclined flat plate configuration, acoustic waves that travel upstream originate from the impingement and wall jet regions. These upstream traveling waves are a combination of the acoustic waves that are produced by the high speed jet flows in the wall jet region and acoustic waves that reflect from the impingement wall. Due to the inclination of the impingement plate, these waves either travel to the far-field in the upstream direction or travel towards the free-jet region interacting with the high speed flow near the nozzle lip. This interaction can create a self sustaining feedback loop, which can cause acoustic tones to appear in the near- and far-field spectra. It is the aim of the present study to block the upstream traveling waves by introducing a second inclined wall with a circular cut-out between the nozzle exit and the impingement plate. Different configurations with different wall locations and cut-out sizes are investigated using a Detached Eddy Simulation CFD solver and an acoustic solver that is based on the Ffowcs Williams and Hawkings analogy. The mechanisms for the establishment of the feedback loops are examined.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65854288","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 : 2023-09-01DOI: 10.1177/1475472x231199189
K. Zaman
A set of 2-inch diameter nozzles is used to investigate the effect of varying exit boundary layer (BL) states on the radiated noise from high-subsonic jets. It is confirmed that nozzles involving turbulent boundary layers are the quietest while others, involving nominally-laminar BLs, are noisier. A turbulent BL is thicker and there is simply an effect of thickness on noise. A thicker BL results in a decrease in the sound pressure spectral amplitudes due to a less vigorous growth of instability waves in the jet’s shear layer. A nominally-laminar BL, besides being thinner, may also involve significantly higher turbulence intensities, much higher than that in a turbulent BL. Such a BL state, referred to as ‘highly disturbed laminar’, results in the largest noise amplitudes especially on the high-frequency side of the spectrum. This transitional state, often encountered with model scale nozzles, involves a ‘Blasius-like’ mean velocity profile but large velocity fluctuation intensities and intermittency. The higher initial turbulence adds to the increase in high-frequency noise. The results leave little doubt that an anomaly noted with subsonic jet noise databases in the literature is due to similar effects of differences in the initial boundary layer state.
{"title":"Initial boundary layer state of typical model-scale jet nozzles and its impact on noise","authors":"K. Zaman","doi":"10.1177/1475472x231199189","DOIUrl":"https://doi.org/10.1177/1475472x231199189","url":null,"abstract":"A set of 2-inch diameter nozzles is used to investigate the effect of varying exit boundary layer (BL) states on the radiated noise from high-subsonic jets. It is confirmed that nozzles involving turbulent boundary layers are the quietest while others, involving nominally-laminar BLs, are noisier. A turbulent BL is thicker and there is simply an effect of thickness on noise. A thicker BL results in a decrease in the sound pressure spectral amplitudes due to a less vigorous growth of instability waves in the jet’s shear layer. A nominally-laminar BL, besides being thinner, may also involve significantly higher turbulence intensities, much higher than that in a turbulent BL. Such a BL state, referred to as ‘highly disturbed laminar’, results in the largest noise amplitudes especially on the high-frequency side of the spectrum. This transitional state, often encountered with model scale nozzles, involves a ‘Blasius-like’ mean velocity profile but large velocity fluctuation intensities and intermittency. The higher initial turbulence adds to the increase in high-frequency noise. The results leave little doubt that an anomaly noted with subsonic jet noise databases in the literature is due to similar effects of differences in the initial boundary layer state.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42980056","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 : 2023-09-01DOI: 10.1177/1475472x231202624
Jeffrey M Mendoza
This paper provides some personal background, technical achievements, and a few testimonials from those who Professor Krishan Kumar Ahuja has worked with throughout his career. I have known Krish as an advisor, a colleague, and as someone I would consider a friend since my graduate school enrollment at Georgia Tech. He not only supported my research in pursuit of an MS and PhD but has been a constant reliable source of technical and professional advice throughout my young career and today, over 30 years later. This paper contains contributions from Krish’s wife Philippa, and from several students and colleagues. It has information from a small subset of many people that Krish has mentored and influenced and worked with over the years. It serves as a starting point for this special edition tribute to Dr Krish Ahuja and his half century of contributions in acoustics. Although Dr. Ahuja’s contributions in jet noise are arguably his most foundational work, he has made significant technical contributions in the areas of cavity noise, engine acoustic liner technologies, rotorcraft and UAV noise, advanced flow and noise measurements and diagnostics, active flow and noise control, and many others. The subsequent papers to follow in this special edition cover a range of topics in areas exemplary to Dr. Ahuja’s career and from authors he has worked with and influenced over the years.
{"title":"Krishan Kumar Ahuja: A brief history and testimonial to the half century of achievements in acoustics","authors":"Jeffrey M Mendoza","doi":"10.1177/1475472x231202624","DOIUrl":"https://doi.org/10.1177/1475472x231202624","url":null,"abstract":"This paper provides some personal background, technical achievements, and a few testimonials from those who Professor Krishan Kumar Ahuja has worked with throughout his career. I have known Krish as an advisor, a colleague, and as someone I would consider a friend since my graduate school enrollment at Georgia Tech. He not only supported my research in pursuit of an MS and PhD but has been a constant reliable source of technical and professional advice throughout my young career and today, over 30 years later. This paper contains contributions from Krish’s wife Philippa, and from several students and colleagues. It has information from a small subset of many people that Krish has mentored and influenced and worked with over the years. It serves as a starting point for this special edition tribute to Dr Krish Ahuja and his half century of contributions in acoustics. Although Dr. Ahuja’s contributions in jet noise are arguably his most foundational work, he has made significant technical contributions in the areas of cavity noise, engine acoustic liner technologies, rotorcraft and UAV noise, advanced flow and noise measurements and diagnostics, active flow and noise control, and many others. The subsequent papers to follow in this special edition cover a range of topics in areas exemplary to Dr. Ahuja’s career and from authors he has worked with and influenced over the years.","PeriodicalId":49304,"journal":{"name":"International Journal of Aeroacoustics","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139345975","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 : 2023-08-26DOI: 10.1177/1475472x231199190
R. Dougherty
Prof. Krish Ahuja has a longstanding interest in jet noise source location. His work in this area is grounded in the idea that if the assumed source location is correct, then the sound should obey the inverse square law relative to that point and the phase should be constant along lines originating at that point. He applied this with, conceptually, one microphone in 1985 and two microphones in 1998. In 2006 he commissioned a beamforming system, Array 48, from OptiNav, Inc. His student, Nick Breen, used this to measure subsonic jet noise source location in detail. The NASA-Glenn Research Center also purchased an Array 48. In the current work, a jet noise data set measured by Gary Podboy using Glenn’s array in 2008 is revisited with a new beamforming algorithm, Robust Functional Beamforming, to further support Tam’s two-source model and Breen’s source location. Beamforming with modified steering vectors is performed to measure the parameters of the wavepacket source model from the far field. This process suggested replacing the wavepacket spatial length parameter with a temporal lifetime parameter. Another steering vector modification aimed to measure modes with odd spinning order. It seems to have found them at an apparent location 10 jet diameters removed from the jet, laterally. This is tentatively interpreted as a Mach radius phenomenon like one observed by Csaba Horvath at NASA-Glenn, also using Array 48, to study counter-rotating propeller noise. In an observation unrelated to beamforming, the excess noise measured at 40° from the jet axis as compared with the 90° angle, is fully contained in the first few cross spectral matrix eigenvalues, or Spectral Proper Orthogonal Decomposition modes, in some cases.
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