Jet Noise Source Localization And Identification

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Jet Noise Source Localization And Identification

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Author : Unnikrishnan Sasidharan Nair
language : en
Publisher:
Release Date : 2017

Jet Noise Source Localization And Identification written by Unnikrishnan Sasidharan Nair and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.

The exact mechanism by which turbulent fluctuations in jets are converted into acoustic energy remains unexplained. The current work aims to improve our understanding of this problem by localizing acoustic sources and identifying its causal dynamics. We use Large-Eddy Simulations of a Mach 1.3 turbulent cold jet for this purpose. The localization question is resolved by using a novel technique, termed Synchronous Large-Eddy Simulations (SLES), that tracks the non-linear evolution of small perturbations from any region (window) in a time-varying base flow. This provides superior insights into the generation of intermittency and directivity compared to traditional approaches that use linear stability analyses based on steady basic states or backward correlations between different regions of the flow. In SLES, two simulations are performed in a lock-step manner. At each step, native fluctuations from a desired spatial window in the first (or baseline simulation) are scaled to small values and then injected into the second (or twin simulation) to provide a forcing in the targeted region. At subsequent times, the difference between the two simulations provides a snapshot of the evolution of the perturbation field associated with the continuous forcing in the chosen spatial window. The perturbation field, which is equivalent to the solution of the forced Navier-Stokes equations linearized about the time-evolving base flow, is then statistically analyzed to identify its modulation by the turbulent region of the jet. Results are distilled by examining forcing at lipline and centerline locations in detail. The end of the potential core is found to be a sensitive zone where perturbations are amplified and lead to secondary sources. Perturbations within the shear layer on the other hand, are initially channeled toward the core and undergo higher amplification compared to those originating from the centerline, before propagating outward. Statistical analyses quantify intermittent events which have a major role in creating the nearfield sound signature and yield polar variation of the most significant frequency band. The flowfield is decomposed into its acoustic, hydrodynamic and thermal modes (which are referred to as the Fluid-Thermodynamic (FT) modes) using the Momentum Potential Theory to identify the acoustic sources and extract the propagated field of the jet. The hydrodynamic mode highlights the shear layer roll up and turbulent mixing, while the acoustic and thermal modes exhibit a wavepacket nature in the core. The acoustic wavepacket develops into the nearfield radiation pattern of the jet, with spatio-temporal amplifications in the core due to the presence of vorticity resulting in nearfield intermittent events. The acoustic and hydrodynamic modes closely follow the theoretical decay rates and the former possess the features of experimentally observed model sound spectra along the downstream and sideline polar angles. Inter-modal energy transfers in the non-linear flow are analyzed using the transport equation for the universal acoustic variable, Total Fluctuating Enthalpy (TFE). Production terms of TFE identify intruding vortices in the potential core as the principal physical mechanism by which intermittent acoustic sources are generated in the jet. The acoustic wavepacket and its nearfield fluctuations play a central role in transporting TFE utward from the core, resulting in the near and farfield sound signature of the jet. The present work provides unique insights into time-accurate linear response of a turbulent jet, and quantifies the relative prominence of various core locations in generating the nearfield acoustic signature. The evolution of the linear perturbation field highlights the modulation of random turbulent fluctuations into spatio-temporally persistent intermittent events. While the intermediate frequencies in the jet propagate in the upstream direction, the highest and lowest frequency-bands prevail in the sideline and downstream directions respectively. The FT mode decomposition elucidates the energy transfer mechanisms in the jet. It provides a phenomenological model to explain the amplification of the acoustic mode, leading to intermittent sound events in the nearfield as well as generation of acoustic sources. The FT modes also quantify the net energy flux scattered and transmitted out of the jet, delineating the stochastic turbulence from a relatively orderly acoustic transport.

Jet Noise Source Localization Using Linear Phased Array

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Author : Nasa Technical Reports Server (Ntrs)
language : en
Publisher: BiblioGov
Release Date : 2013-07

Jet Noise Source Localization Using Linear Phased Array written by Nasa Technical Reports Server (Ntrs) and has been published by BiblioGov this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-07 with categories.

A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics sources in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet noise sources with bypass and other components separation. The results also showed that a focused near field image provides more realistic noise source localization at low to mid frequencies.

Jet Noise Source Localization Using Linear Phased Array

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Author : National Aeronautics and Space Administration (NASA)
language : en
Publisher: Createspace Independent Publishing Platform
Release Date : 2018-06-21

Jet Noise Source Localization Using Linear Phased Array written by National Aeronautics and Space Administration (NASA) and has been published by Createspace Independent Publishing Platform this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-06-21 with categories.

A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics sources in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet noise sources with bypass and other components separation. The results also showed that a focused near field image provides more realistic noise source localization at low to mid frequencies. Agboola, Ferni A. and Bridges, James Glenn Research Center NASA/TM-2004-213041, E-14478

Phased Array Design Validation And Applications To Jet Noise Source Localization

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Author : S. R. Venkatesh
language : en
Publisher:
Release Date : 2000

Phased Array Design Validation And Applications To Jet Noise Source Localization written by S. R. Venkatesh and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with categories.

Phased Array Noise Source Localization Measurements Of An F404 Nozzle Plume At Both Full And Model Scale

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Author : National Aeronautics and Space Administration (NASA)
language : en
Publisher: Createspace Independent Publishing Platform
Release Date : 2018-05-20

Phased Array Noise Source Localization Measurements Of An F404 Nozzle Plume At Both Full And Model Scale written by National Aeronautics and Space Administration (NASA) and has been published by Createspace Independent Publishing Platform this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-05-20 with categories.

A 48-microphone planar phased array system was used to acquire jet noise source localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant noise sources in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic source localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet noise source mechanisms, and document some of the differences associated with testing at model-scale versus fullscale. Podboy, Gary G. and Bridges, James E. and Henderson, Brenda S. Glenn Research Center JET AIRCRAFT NOISE; NOISE GENERATORS; SOUND GENERATORS; ENGINE NOISE; ENGINE TESTS; FULL SCALE TESTS; PHASED ARRAYS; PLUMES; PLANAR STRUCTURES; SCALE MODELS

Phased Array Noise Source Localization Measurements Of An F404 Nozzle Plume At Both Full And Model Scale

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Author : Nasa Technical Reports Server (Ntrs)
language : en
Publisher: BiblioGov
Release Date : 2013-07

Phased Array Noise Source Localization Measurements Of An F404 Nozzle Plume At Both Full And Model Scale written by Nasa Technical Reports Server (Ntrs) and has been published by BiblioGov this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-07 with categories.

A 48-microphone planar phased array system was used to acquire jet noise source localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant noise sources in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic source localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet noise source mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.

Jet Surface Interaction Test

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Author : Gary G. Podboy
language : en
Publisher:
Release Date : 2013

Jet Surface Interaction Test written by Gary G. Podboy and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.

Further Progress In Noise Source Identification In High Speed Jets Via Causality Principle

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Author : National Aeronautics and Space Administration (NASA)
language : en
Publisher: Createspace Independent Publishing Platform
Release Date : 2018-05-31

Further Progress In Noise Source Identification In High Speed Jets Via Causality Principle written by National Aeronautics and Space Administration (NASA) and has been published by Createspace Independent Publishing Platform this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-05-31 with categories.

To locate noise sources in high-speed jets, the sound pressure fluctuations p/, measured at far field locations, were correlated with each of density p, axial velocity u, radial velocity v, puu and pvv fluctuations measured from various points in fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering (Seasholtz, Panda, and Elam, AIAA Paper 2002-0827). The technique uses a continuous wave, narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. The far field sound pressure fluctuations at 30 to the jet axis provided the highest correlation coefficients with all flow variables. The correlation coefficients decreased sharply with increased microphone polar angle, and beyond about 60 all correlation mostly fell below the experimental noise floor. Among all correlations showed the highest values. Interestingly, , in all respects, were very similar to . The and correlations with 90deg microphone fell below the noise floor. By moving the laser probe at various locations in the jet it was found that the strongest noise source lies downstream of the end of the potential core and extends many diameters beyond. Correlation measurement from the lip shear layer showed a Mach number dependency. While significant correlations were measured in Mach 1.8 jet, values were mostly below the noise floor for subsonic Mach 0.95 jet. Various additional analyses showed that fluctuations from large organized structures mostly contributed to the measured correlation, while that from small scale structures fell below the noise floor.Panda, J. and Seasholtz, R. G. and Elam, K. A.Glenn Research CenterNOISE (SOUND); JET AIRCRAFT NOISE; RAYLEIGH SCATTERING; SOUND PRESSURE; NOISE GENERATORS; PRESSURE OSCILLATIONS;

Noise Identification In A Hot Transonic Jet Using Low Dimensional Methods

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Author : André M. Hall
language : en
Publisher:
Release Date : 2008

Noise Identification In A Hot Transonic Jet Using Low Dimensional Methods written by André M. Hall and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Computational fluid dynamics categories.

The goal of this effort has been to identify the dominant source of the radiated aero-acoustic noise produced by high-speed, heated jets and develop control strategies to reduce it. To that end, two acoustically matched Mach 0.6 jets, at temperature ratio Tr=O.93 (cold) and Tr=1.7 (hot) are examined. The use of non-intrusive Particle Image Velocimetry (PIV) to sample the flow, allowed a true measure of the velocity field to be realized without fear of corrupting the radiated noise field intrinsic to each jet. The low-order modal dominance of each was determined using Proper Orthogonal Decomposition (POD), highlighting the low-dimensional nature of this highly turbulent flow field.

Acoustic Noise Source Identification In Aircraft Based Atmospheric Temperature Measurements

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Author : Ron Hugo
language : en
Publisher:
Release Date : 1999

Acoustic Noise Source Identification In Aircraft Based Atmospheric Temperature Measurements written by Ron Hugo and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1999 with categories.