G. Yakhina, M. Roger, A. Finez, Valentin Baron, S. Moreau, Justine Giez
{"title":"Broadband Airfoil-Noise Source Localization by Microphone Arrays and Modeling of a Swept Free-Tip Blade","authors":"G. Yakhina, M. Roger, A. Finez, Valentin Baron, S. Moreau, Justine Giez","doi":"10.2514/6.2018-3935","DOIUrl":"https://doi.org/10.2514/6.2018-3935","url":null,"abstract":"","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"278 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123429671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Two types of aeroacoustic wind tunnel test section configurations have been tested in the NASA Langley Quiet Flow Facility. The first is a more traditional open-jet configuration, where test section flow passes unbounded through the facility anechoic chamber. The second is the more recent Kevlar wall configuration, where a tensioned Kevlar sheet bounds the test section flow from the facility anechoic chamber. For both configurations, acoustic instrumentation is in the surrounding quiescent space. Both configurations are evaluated with a laser-based pulsed acoustic source, which provides unique capability for assessing the facility unsteady acoustic propagation characteristics. Metrics based on the wander and spread of the pulses are evaluated and show that measurements using Kevlar walls experience dramatically reduced unsteady effects when compared to the open-jet configuration. This leads to a corresponding improvement in coherence between microphones with the Kevlar configuration. Corrections for magnitude and phase for propagation through Kevlar as compared to open-jet propagation are calculated. While limitations in the experimental setup make quantitative analysis difficult, qualitative analysis shows Kevlar magnitude corrections similar to those determined in previous literature. Directivity effects beyond those already present for open-jet configurations are minimal. Phase corrections relative to open-jet configurations are indeterminate within the limitations of the experiment, though data suggest such corrections are not extreme. The background noise produced by the Kevlar is found to be its one drawback when compared with the open-jet configuration, showing significantly greater levels at high frequencies.
{"title":"Assessment of Unsteady Propagation Characteristics and Corrections in Aeroacoustic Wind Tunnels Using an Acoustic Pulse","authors":"C. Bahr, F. Hutcheson, Daniel J. Stead","doi":"10.2514/6.2018-3118","DOIUrl":"https://doi.org/10.2514/6.2018-3118","url":null,"abstract":"Two types of aeroacoustic wind tunnel test section configurations have been tested in the NASA Langley Quiet Flow Facility. The first is a more traditional open-jet configuration, where test section flow passes unbounded through the facility anechoic chamber. The second is the more recent Kevlar wall configuration, where a tensioned Kevlar sheet bounds the test section flow from the facility anechoic chamber. For both configurations, acoustic instrumentation is in the surrounding quiescent space. Both configurations are evaluated with a laser-based pulsed acoustic source, which provides unique capability for assessing the facility unsteady acoustic propagation characteristics. Metrics based on the wander and spread of the pulses are evaluated and show that measurements using Kevlar walls experience dramatically reduced unsteady effects when compared to the open-jet configuration. This leads to a corresponding improvement in coherence between microphones with the Kevlar configuration. Corrections for magnitude and phase for propagation through Kevlar as compared to open-jet propagation are calculated. While limitations in the experimental setup make quantitative analysis difficult, qualitative analysis shows Kevlar magnitude corrections similar to those determined in previous literature. Directivity effects beyond those already present for open-jet configurations are minimal. Phase corrections relative to open-jet configurations are indeterminate within the limitations of the experiment, though data suggest such corrections are not extreme. The background noise produced by the Kevlar is found to be its one drawback when compared with the open-jet configuration, showing significantly greater levels at high frequencies.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123929775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Rossian, A. Suryadi, Karl-Stéphane Rossignol, R. Ewert, M. Herr, J. Delfs, Pradeep Kumar
With the advances in reduction of propulsion related noise from aircraft, airframe noise gets more and more into focus. During approach and landing, the high-lift system of the wings becomes one major acoustic source region contributing to the overall emitted noise. One promising approach to reduce this airframe noise is to change the complete high-lift system from a classic three element slat-wing-flap configuration to a slot-less system with active blowing and droop nose. Preceding experimental investigations have shown, that such a configuration may provide a noise reduction above 2 kHz on the model scale. In the present paper both numerical and experimental investigations concerning the acoustics of a high-lift wing with droop nose and active blowing are presented. Thereby, an insight into the acoustic source mechanisms for different aerodynamic setups is provided that in the future will serve as a basis for the design of a low-noise high-lift configuration. It was found, that in principle three source mechanisms are to be considered. In the low to mid frequency domain, mostly turbulence-geometry interaction noise such as trailing edge noise, jet-nozzle interaction noise and curvature noise from the flow being bent around the flap are supposed to be the driving mechanisms. Moreover, the high frequency domain is found to be dominated by mixing noise from the high speed jet.
{"title":"Numerical and experimental insights into the noise generation of a circulation control airfoil","authors":"L. Rossian, A. Suryadi, Karl-Stéphane Rossignol, R. Ewert, M. Herr, J. Delfs, Pradeep Kumar","doi":"10.2514/6.2018-3139","DOIUrl":"https://doi.org/10.2514/6.2018-3139","url":null,"abstract":"With the advances in reduction of propulsion related noise from aircraft, airframe noise \u0000gets more and more into focus. During approach and landing, the high-lift system of the \u0000wings becomes one major acoustic source region contributing to the overall emitted noise. \u0000One promising approach to reduce this airframe noise is to change the complete high-lift \u0000system from a classic three element slat-wing-flap configuration to a slot-less system with \u0000active blowing and droop nose. Preceding experimental investigations have shown, that \u0000such a configuration may provide a noise reduction above 2 kHz on the model scale. In the \u0000present paper both numerical and experimental investigations concerning the acoustics of \u0000a high-lift wing with droop nose and active blowing are presented. Thereby, an insight \u0000into the acoustic source mechanisms for different aerodynamic setups is provided that in \u0000the future will serve as a basis for the design of a low-noise high-lift configuration. It \u0000was found, that in principle three source mechanisms are to be considered. In the low to \u0000mid frequency domain, mostly turbulence-geometry interaction noise such as trailing edge \u0000noise, jet-nozzle interaction noise and curvature noise from the flow being bent around the \u0000flap are supposed to be the driving mechanisms. Moreover, the high frequency domain is \u0000found to be dominated by mixing noise from the high speed jet.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"441 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125774322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A vehicle-level noise assessment has been performed for the NASA D8 concept aircraft (ND8) in the NASA Advanced Air Transport Technology Project portfolio. The NASA research-level Aircraft NOise Prediction Program (ANOPP-Research) was used to predict the noise from each source component on the ND8 to build up a noise estimate for the full aircraft. The propulsion airframe aeroacoustic (PAA) effects of the ND8, namely boundary layer ingestion (BLI) with its influence on fan noise, and the noise shielding, reflection, and diffraction mechanisms of the unconventional airframe, were empirically modeled using experimental data. Noise reduction technologies appropriate to the 2025-2035 time frame were included in this study. Including all technologies and PAA effects, the ND8 is predicted to have a cumulative margin to the Stage 4 certification metric of only 7.4 EPNdB. Boundary layer ingestion is predicted to have a detrimental impact on cumulative noise levels on the order of 15 EPNdB. Fan noise is seen to be the primary noise source at all three certification points, even if the BLI noise impact could be entirely suppressed. The impact of engine noise shielding by the airframe is limited by a lack of aft shielding and the presence of horizontal tail reflections in the aft direction. The physical constraint on engine size by the pi-tail is seen as a potential barrier to engine noise reduction through the corresponding limitation on fan bypass ratio. Mildly reduced climb performance (compared to similar reference aircraft) does not provide any benefit through increased noise propagation distance. If the boundary layer ingestion noise penalty could be suppressed such that BLI would have no effect on noise, the cumulative margin to Stage 4 would increase to 22.4 EPNdB, still below the NASA Mid Term goal of 32-42 EPNdB. with earlier The was attached to a Grumman and past a series of 30-ft microphones. Their results indicated that the inflow control devices tested previously led to a good representation of the measured BPF levels in flight. They also present results for broadband noise levels at static conditions and in flight, taken as the spectral level at the base of the BPF peaks. They show a significant influence of inflow distortion on broadband noise, up to 6 dB across a wide range of polar angles. This study represents the best comparison of results from this project, and so greatly informs the turbulence ingestion model for the present study.
{"title":"Aircraft System Noise Assessment of the NASA D8 Subsonic Transport Concept","authors":"I. Clark, Russell H. Thomas, Yueping Guo","doi":"10.2514/6.2018-3124","DOIUrl":"https://doi.org/10.2514/6.2018-3124","url":null,"abstract":"A vehicle-level noise assessment has been performed for the NASA D8 concept aircraft (ND8) in the NASA Advanced Air Transport Technology Project portfolio. The NASA research-level Aircraft NOise Prediction Program (ANOPP-Research) was used to predict the noise from each source component on the ND8 to build up a noise estimate for the full aircraft. The propulsion airframe aeroacoustic (PAA) effects of the ND8, namely boundary layer ingestion (BLI) with its influence on fan noise, and the noise shielding, reflection, and diffraction mechanisms of the unconventional airframe, were empirically modeled using experimental data. Noise reduction technologies appropriate to the 2025-2035 time frame were included in this study. Including all technologies and PAA effects, the ND8 is predicted to have a cumulative margin to the Stage 4 certification metric of only 7.4 EPNdB. Boundary layer ingestion is predicted to have a detrimental impact on cumulative noise levels on the order of 15 EPNdB. Fan noise is seen to be the primary noise source at all three certification points, even if the BLI noise impact could be entirely suppressed. The impact of engine noise shielding by the airframe is limited by a lack of aft shielding and the presence of horizontal tail reflections in the aft direction. The physical constraint on engine size by the pi-tail is seen as a potential barrier to engine noise reduction through the corresponding limitation on fan bypass ratio. Mildly reduced climb performance (compared to similar reference aircraft) does not provide any benefit through increased noise propagation distance. If the boundary layer ingestion noise penalty could be suppressed such that BLI would have no effect on noise, the cumulative margin to Stage 4 would increase to 22.4 EPNdB, still below the NASA Mid Term goal of 32-42 EPNdB. with earlier The was attached to a Grumman and past a series of 30-ft microphones. Their results indicated that the inflow control devices tested previously led to a good representation of the measured BPF levels in flight. They also present results for broadband noise levels at static conditions and in flight, taken as the spectral level at the base of the BPF peaks. They show a significant influence of inflow distortion on broadband noise, up to 6 dB across a wide range of polar angles. This study represents the best comparison of results from this project, and so greatly informs the turbulence ingestion model for the present study.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124623064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Adil Cader, C. Polacsek, T. L. Garrec, R. Barrier, F. Benjamin, Marc C. Jacob
Turbulent RSI (rotor-stator interaction) mechanism is a major broadband source contribution of turbofan noise generation. Acoustic prediction tools used by Industry are based on flat-plate cascade response models with restrictive assumptions on flow and geometry. Due to huge CPU memory and time cost required, Large Eddy Simulations of the complete fan-OGV stage are still out of reach (apart from recent impressive results obtained using the Lattice Boltzmann Method). This paper presents an alternative approach based on the use of a 3-D CAA (Computational Aeroacoustics) code solving the linearized-Euler equations applied to the disturbances and coupled with a synthetic turbulence injection model. The inflow turbulence is synthetized by means of a sum of harmonic gusts with random phases. The Fourier-mode amplitudes are trimmed by a 2 or 3-wave number Von-Karman or Liepmann turbulence spectrum. Swirling convection of the synthetic turbulence is provided by a 3D RANS mean flow solution and interpolated at the nodes of the CAA grid. In this paper, our methodology is first validated on a benchmark case (fully annular duct with swirling flow and a prescribed turbulence) and then applied for the first time to an industrial turbofan in the framework of a European project, TurboNoiseBB. Previous implemented 2D formulation (2-wave number spectrum) for turbulence generation is extended here to 3D (axial, radial, and angular modes) in order to study the sensitivity on cascade effects.
{"title":"Numerical prediction of rotor-stator interaction noise using 3D CAA with synthetic turbulence injection","authors":"Adil Cader, C. Polacsek, T. L. Garrec, R. Barrier, F. Benjamin, Marc C. Jacob","doi":"10.2514/6.2018-4190","DOIUrl":"https://doi.org/10.2514/6.2018-4190","url":null,"abstract":"Turbulent RSI (rotor-stator interaction) mechanism is a major broadband source contribution of turbofan noise generation. Acoustic prediction tools used by Industry are based on flat-plate cascade response models with restrictive assumptions on flow and geometry. Due to huge CPU memory and time cost required, Large Eddy Simulations of the complete fan-OGV stage are still out of reach (apart from recent impressive results obtained using the Lattice Boltzmann Method). This paper presents an alternative approach based on the use of a 3-D CAA (Computational Aeroacoustics) code solving the linearized-Euler equations applied to the disturbances and coupled with a synthetic turbulence injection model. The inflow turbulence is synthetized by means of a sum of harmonic gusts with random phases. The Fourier-mode amplitudes are trimmed by a 2 or 3-wave number Von-Karman or Liepmann turbulence spectrum. Swirling convection of the synthetic turbulence is provided by a 3D RANS mean flow solution and interpolated at the nodes of the CAA grid. In this paper, our methodology is first validated on a benchmark case (fully annular duct with swirling flow and a prescribed turbulence) and then applied for the first time to an industrial turbofan in the framework of a European project, TurboNoiseBB. Previous implemented 2D formulation (2-wave number spectrum) for turbulence generation is extended here to 3D (axial, radial, and angular modes) in order to study the sensitivity on cascade effects.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129822514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
James B. Lewis, R. Mankbadi, V. Golubev, L. Nguyen, Saman Salehian
{"title":"A Validation of High-Order Compact ILES Code for Trailing-Edge Noise at High Reynolds Numbers","authors":"James B. Lewis, R. Mankbadi, V. Golubev, L. Nguyen, Saman Salehian","doi":"10.2514/6.2018-3128","DOIUrl":"https://doi.org/10.2514/6.2018-3128","url":null,"abstract":"","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127282682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acoustic localization of gunshots is of interest for protecting security camps in contested forests, increasing soldiers’ situation awareness in ambushes, as well as in guarding cities. All these scenarios are also fraught with obstacles coming in the path of acoustic waves. We present a computational study of the effect of obstacles on the accuracy of localization of point sound sources like gunshots. The two-dimensional linearized Euler equations are solved with the dispersion relation preserving scheme. The localization is performed using the wavefront curvature method based on pressure signatures recorded at three virtual microphones. We report at most 8◦ of error in the estimated bearing angle of the source across a range of practical values of five parameters – viz. the location and size of the obstacle, and the size, orientation and location of the sensor array relative to the source. This level of error may be quite acceptable in the scenarios considered. On the other hand, the range error is much more severe, exceeding 100% of the true range in a few cases. In the scenarios considered, the bearing angle estimate is much more critical than the range estimate. Overall, we conclude that acoustic localization approaches are quite robust in the presence of obstacles.
{"title":"Acoustic Localisation of Gunshots in the Presence of Obstacles","authors":"A. Sinha, Tushar Singh","doi":"10.2514/6.2018-3123","DOIUrl":"https://doi.org/10.2514/6.2018-3123","url":null,"abstract":"Acoustic localization of gunshots is of interest for protecting security camps in contested forests, increasing soldiers’ situation awareness in ambushes, as well as in guarding cities. All these scenarios are also fraught with obstacles coming in the path of acoustic waves. We present a computational study of the effect of obstacles on the accuracy of localization of point sound sources like gunshots. The two-dimensional linearized Euler equations are solved with the dispersion relation preserving scheme. The localization is performed using the wavefront curvature method based on pressure signatures recorded at three virtual microphones. We report at most 8◦ of error in the estimated bearing angle of the source across a range of practical values of five parameters – viz. the location and size of the obstacle, and the size, orientation and location of the sensor array relative to the source. This level of error may be quite acceptable in the scenarios considered. On the other hand, the range error is much more severe, exceeding 100% of the true range in a few cases. In the scenarios considered, the bearing angle estimate is much more critical than the range estimate. Overall, we conclude that acoustic localization approaches are quite robust in the presence of obstacles.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"119 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132081777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Computational results for a full-scale simulation of a Gulfstream G-III aircraft are presented. In support of a NASA airframe noise flight test campaign, Exa Corporation’s lattice Boltzmann PowerFLOW ® solver was used to perform time-accurate simulations of the flow around a highly detailed, full-scale aircraft model. Free-air boundary conditions were used at a Mach number of 0.23 and a Reynolds number of 10.5 × 10 6 based on mean aerodynamic chord. This paper documents the simulation campaign for the baseline aircraft configuration at several flight conditions, including multiple flap deflections and main landing gear deployed or retracted. The high-fidelity, synthetic data were post-processed using a Ffowcs-Williams and Hawkings integral approach to estimate farfield acoustic behavior, with pressures on the model solid surface or a permeable surface enveloping the acoustic near field used as input. The numerical approach, simulation attributes, and the effects of grid resolution, gear deployment, and multiple flap deflections, are discussed as well.
{"title":"Airframe Noise Simulations of a Full-Scale Aircraft","authors":"J. Appelbaum, B. Duda, E. Fares, M. Khorrami","doi":"10.2514/6.2018-2973","DOIUrl":"https://doi.org/10.2514/6.2018-2973","url":null,"abstract":"Computational results for a full-scale simulation of a Gulfstream G-III aircraft are presented. In support of a NASA airframe noise flight test campaign, Exa Corporation’s lattice Boltzmann PowerFLOW ® solver was used to perform time-accurate simulations of the flow around a highly detailed, full-scale aircraft model. Free-air boundary conditions were used at a Mach number of 0.23 and a Reynolds number of 10.5 × 10 6 based on mean aerodynamic chord. This paper documents the simulation campaign for the baseline aircraft configuration at several flight conditions, including multiple flap deflections and main landing gear deployed or retracted. The high-fidelity, synthetic data were post-processed using a Ffowcs-Williams and Hawkings integral approach to estimate farfield acoustic behavior, with pressures on the model solid surface or a permeable surface enveloping the acoustic near field used as input. The numerical approach, simulation attributes, and the effects of grid resolution, gear deployment, and multiple flap deflections, are discussed as well.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130900222","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Luigi A. Antonialli, A. Cavalieri, O. Schmidt, T. Colonius, A. Towne, G. Brès, P. Jordan
Wavepackets modelling large-scale coherent structures are related to the peak noise radiation by subsonic jets. Such wavepacket models are well developed in the literature, and are often based on a linearization of the Navier-Stokes system; solutions of the resulting linear problem have a free amplitude, which can be obtained by comparison with experiments or simulations. In this work we determine amplitudes of turbulent-jet wavepackets by comparing large-eddy simulation (LES) data from Br`es et al. of a Mach 0.9 jet and fluctuation fields using the parabolized stability equations (PSE) model (Sasaki et al.). Projection of the leading mode from spectral proper orthogonal decomposition (SPOD), applied to the LES data, onto the PSE model solutions is a way to determine the free amplitude, and by analyzing such amplitudes for different Strouhal numbers and azimuthal modes of the turbulent jet, it is possible to notice a clear pattern of the scaling factor with varying St. Azimuthal wavenumbers m = 0, 1 and 2 show an exponential dependence of wavepacket amplitude with Strouhal number. This sheds light on how wavepackets amplitudes behave and how they are excited upstream.
{"title":"Amplitude scaling of turbulent-jet wavepackets","authors":"Luigi A. Antonialli, A. Cavalieri, O. Schmidt, T. Colonius, A. Towne, G. Brès, P. Jordan","doi":"10.2514/6.2018-2978","DOIUrl":"https://doi.org/10.2514/6.2018-2978","url":null,"abstract":"Wavepackets modelling large-scale coherent structures are related to the peak noise radiation by subsonic jets. Such wavepacket models are well developed in the literature, and are often based on a linearization of the Navier-Stokes system; solutions of the resulting linear problem have a free amplitude, which can be obtained by comparison with experiments or simulations. In this work we determine amplitudes of turbulent-jet wavepackets by comparing large-eddy simulation (LES) data from Br`es et al. of a Mach 0.9 jet and fluctuation fields using the parabolized stability equations (PSE) model (Sasaki et al.). Projection of the leading mode from spectral proper orthogonal decomposition (SPOD), applied to the LES data, onto the PSE model solutions is a way to determine the free amplitude, and by analyzing such amplitudes for different Strouhal numbers and azimuthal modes of the turbulent jet, it is possible to notice a clear pattern of the scaling factor with varying St. Azimuthal wavenumbers m = 0, 1 and 2 show an exponential dependence of wavepacket amplitude with Strouhal number. This sheds light on how wavepackets amplitudes behave and how they are excited upstream.","PeriodicalId":429337,"journal":{"name":"2018 AIAA/CEAS Aeroacoustics Conference","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123386536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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