Relevant bibliographies by topics / Far-field directivity

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers

Academic literature on the topic 'Far-field directivity'

Author: Grafiati
Published: 4 June 2021
Last updated: 1 February 2022

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Journal articles on the topic "Far-field directivity"

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Jiang Shuang-Feng, Kong Fan-Min, Li Kang, and Gao Hui. "Study of far-field directivity of optical dipole antenna." Acta Physica Sinica 60, no. 4 (2011): 045203. http://dx.doi.org/10.7498/aps.60.045203.

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Shahbazi, Shahrokh, Iman Mansouri, Jong Wan Hu, Noura Sam Daliri, and Armin Karami. "Seismic Response of Steel SMFs Subjected to Vertical Components of Far- and Near-Field Earthquakes with Forward Directivity Effects." Advances in Civil Engineering 2019 (April 3, 2019): 1–15. http://dx.doi.org/10.1155/2019/2647387.

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In the near-field earthquake, forward directivity effects cause long-period pulse with a short effective time and a large domain in the velocity time history. This issue increases the ductility needs of structures, and in recent decades, the destructive effects of these kinds of records have been evaluated in comparison with far-field earthquakes. This brings about the necessity to compare a structure’s behavior subjected to vertical components of near-field (NF) earthquakes, including forward directivity effects vs. the effects of vertical components of far-field (FF) earthquakes. The present study investigated 3-, 5-, 8-, and 20-story steel moment frames with special ductility (SMF) through which modeling effects of panel zone have been applied, subjected to vertical component of near-field (NF) earthquakes with forward directivity and the vertical component of far-field earthquakes. By investigating the results, it can be clearly seen that the average values of the maximum displacement, shear force of the stories, and the velocity of each story under the impact of the near-field earthquake are greater than the amount of that under the effect of a far-field earthquake. However, this comparison is not valid for the amount of acceleration, axial force, and moments in the columns of the structures accurately.
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OBRIST, DOMINIK. "Directivity of acoustic emissions from wave packets to the far field." Journal of Fluid Mechanics 640 (November 10, 2009): 165–86. http://dx.doi.org/10.1017/s0022112009991297.

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We investigate the acoustic emission from wave packets to the far field. To this end, we develop a theory for one- and two-dimensional source fields in the shape of wave packets with Gaussian envelopes. This theory is based on an approximation to Lighthill's acoustic analogy for distant observers. It is formulated in the spectral domain in which a Gaussian wave packet is represented again by a Gaussian. This allows us to determine the directivity of the acoustic emission (e.g. superdirectivity and Mach waves) by simple geometric constructions in the spectral domain. It is shown that the character of the acoustic emission is mainly governed by the aspect ratio and the Mach number of the wave packet source. To illustrate the relevance of this theory we use it to study two prominent problems in subsonic jet aeroacoustics.
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Post, John T., and Elmer L. Hixson. "Measurement of throat impedance and far‐field directivity for acoustic horns." Journal of the Acoustical Society of America 96, no. 5 (November 1994): 3290. http://dx.doi.org/10.1121/1.410911.

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Guasch, Oriol, and Patricia Sánchez-Martín. "Far-field directivity of parametric loudspeaker arrays set on curved surfaces." Applied Mathematical Modelling 60 (August 2018): 721–38. http://dx.doi.org/10.1016/j.apm.2018.04.002.

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Chiselev, Ana-Maria, and Luminita Moraru. "A Study of Far Field Directivity Pattern of Bio-Inspired EMFit Emitters." IEEE Sensors Journal 12, no. 5 (May 2012): 1372–76. http://dx.doi.org/10.1109/jsen.2011.2172600.

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Soh, W. Y. "Numerical simulation of free shear flows and far-field sound pressure directivity." International Journal for Numerical Methods in Fluids 18, no. 4 (February 28, 1994): 337–59. http://dx.doi.org/10.1002/fld.1650180403.

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Bakker, Maarten C. M., and Martin D. Verweij. "An approximation to the far field and directivity of elastic wave transducers." Journal of the Acoustical Society of America 111, no. 3 (March 2002): 1177–88. http://dx.doi.org/10.1121/1.1428542.

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Zhong, Siyang, and Xin Zhang. "A sound extrapolation method for aeroacoustics far-field prediction in presence of vortical waves." Journal of Fluid Mechanics 820 (May 8, 2017): 424–50. http://dx.doi.org/10.1017/jfm.2017.219.

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Off-surface integral solutions to an inhomogeneous wave equation based on acoustic analogy could suffer from spurious wave contamination when volume integrals are ignored for computation efficiency and vortical/turbulent gusts are convected across the integration surfaces, leading to erroneous far-field directivity predictions. Vortical gusts often exist in aerodynamic flows and it is inevitable their effects are present on the integration surface. In this work, we propose a new sound extrapolation method for acoustic far-field directivity prediction in the presence of vortical gusts, which overcomes the deficiencies in the existing methods. The Euler equations are rearranged to an alternative form in terms of fluctuation variables that contains the possible acoustical and vortical waves. Then the equations are manipulated to an inhomogeneous wave equation with source terms corresponding to surface and volume integrals. With the new formulation, spurious monopole and dipole noise produced by vortical gusts can be suppressed on account of the solenoidal property of the vortical waves and a simple convection process. It is therefore valid to ignore the volume integrals and preserve the sound properties. The resulting new acoustic inhomogeneous convected wave equations could be solved by means of the Green’s function method. Validation and verification cases are investigated, and the proposed method shows a capacity of accurate sound prediction for these cases. The new method is also applied to the challenging airfoil leading edge noise problems by injecting vortical waves into the computational domain and performing aeroacoustic studies at both subsonic and transonic speeds. In the case of a transonic airfoil leading edge noise problem, shocks are present on the airfoil surface. Good agreements of the directivity patterns are obtained compared with direct computation results.
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Vatanshenas, Ali, Mohammad Sadegh Rohanimanesh, and Ehsan Mohammadiha. "Investigating the Performance of Viscoelastic Dampers (VED) Under Nearfield Earthquakes with Directivity Feature." Civil and Environmental Engineering 14, no. 1 (June 1, 2018): 21–27. http://dx.doi.org/10.2478/cee-2018-0003.

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AbstractOne of the most important factors that make structures vulnerable to earthquakes is the short distance between structures and epicenter. Near-field earthquakes have special properties, such as increasing acceleration applied to the structure, which distinguishes them from far-field earthquakes. Therefore, the absorption of input energy for structures located near the faults is very important. Hence, by rotating the earthquake acceleration time history and comparing the resulting spectral acceleration response, the angle which applies the greatest force to the structure on the earthquake directivity side is obtained, and then the performance of a steel structure with viscoelastic dampers (VED) under near-field earthquakes with directivity feature is investigated. After analyzing the structure using nonlinear time history analysis, it was observed that the directivity phenomenon leads to significant increase in the force applied to the structure, but the viscoelastic dampers showed an acceptable performance in both states of with and without directivity.
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Dissertations / Theses on the topic "Far-field directivity"

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Eyring, Nicholas J. "Development and Validation of an Automated Directivity Acquisition System Used in the Acquisition, Processing, and Presentation of the Acoustic Far-Field Directivity of Musical Instruments in an Anechoic Space." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4004.

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A high spatial resolution acoustic directivity acquisition system (ADAS) has been developed to acquire anechoic measurements of the far field radiation of musical instruments that are either remote controlled or played by musicians. Building upon work performed by the BYU Acoustic Research Group in the characterization of loudspeaker directivity, one can rotate a musical instrument with sequential azimuthal angle increments under a fixed semicircular array of microphones while recording repeated notes or sequences of notes. This results in highly detailed and instructive directivity data presented in the form of high-resolution balloon plots. The directivity data and corresponding balloon plots may be shown to vary as functions of time or frequency. This thesis outlines the development of a prototype ADAS and its application to different sources including loudspeakers, a concert grand piano, trombone, flute, and violin. The development of a method of compensating for variations in the played amplitude at subsequent measurement positions using a near-field reference microphone and Frequency Response Functions (FRF) is presented along with the results of its experimental validation. This validation involves a loudspeaker, with known directivity, to simulate a live musician. It radiates both idealized signals and anechoic recordings of musical instruments with random variations in amplitude. The concept of coherence balloon maps and surface averaged coherence are introduced as tools to establish directivity confidence. The method of creating composite directivities for musical instruments is also introduced. A composite directivity comes from combining the directivities of all played partials to approximate what the equivalent directivity from a musical instrument would be if full spectral excitation could be used. The composite directivities are derived from an iterative averaging process that uses coherence as an inclusion criterion. Sample directivity results and discussions of experimental considerations of the piano, trombone, flute, and violin are presented. The research conducted is preliminary and will be further developed by future students to expand and refine the methods presented here.
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(10867179), Abigail Jubilee Kragt Finnell. "Wireless Power Transfer: Efficiency, Far Field, Directivity, and Phased Array Antennas." Thesis, 2021.

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This thesis is an examination of one of the main technologies to be developed on the path to Space Solar Power (SSP): Wireless Power Transfer (WPT), specifically power beaming. While SSP has been the main motivation for this body of work, other applications of power beaming include ground-to-ground energy transfer, ground to low-flying satellite wireless power transfer, mother-daughter satellite configurations, and even ground-to-car or ground-to-flying-car power transfer. More broadly, Wireless Power Transfer falls under the category of radio and microwave signals; with that in mind, some of the topics contained within can even be applied to 5G or other RF applications. The main components of WPT are signal transmission, propagation, and reception. This thesis focuses on the transmission and propagation of wireless power signals, including beamforming with Phased Array Antennas (PAAs) and evaluations of transmission and propagation efficiency. Signals used to transmit power long distances must be extremely directive in order to deliver the power at an acceptable efficiency and to prevent excess power from interfering with other RF technology. Phased array antennas offer one method of increasing the directivity of a transmitted beam through off-axis cancellation from the multi-antenna source. Besides beamforming, another focus of this work is on the equations used to describe the efficiency and far field distance of transmitting antennas. Most previously used equations, including the Friis equation and the Goubau equation, are formed by examining singleton antennas, and do not account for the unique properties of antenna arrays. Updated equations and evaluation methods are presented both for the far field and the efficiency of phased array antennas. Experimental results corroborate the far field model and efficiency equation presented, and the implications of these results regarding space solar power and other applications are discussed. The results of this thesis are important to the applications of WPT previously mentioned, and can also be used as a starting point for further WPT and SSP research, especially when looking at the foundations of PAA technology.
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Finnell, Jubilee Kragt Finnell. "Wireless Power Transfer: Efficiency, Far Field, Directivity, and Phased Array Antennas." Thesis, 2021. http://dx.doi.org/10.7912/C2/44.

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Indiana University-Purdue University Indianapolis (IUPUI)
This thesis is an examination of one of the main technologies to be developed on the path to Space Solar Power (SSP): Wireless Power Transfer (WPT), specifically power beaming. While SSP has been the main motivation for this body of work, other applications of power beaming include ground-to-ground energy transfer, ground to low-flying satellite wireless power transfer, mother-daughter satellite configurations, and even ground-to-car or ground-to-flying-car power transfer. More broadly, Wireless Power Transfer falls under the category of radio and microwave signals; with that in mind, some of the topics contained within can even be applied to 5G or other RF applications. The main components of WPT are signal transmission, propagation, and reception. This thesis focuses on the transmission and propagation of wireless power signals, including beamforming with Phased Array Antennas (PAAs) and evaluations of transmission and propagation efficiency. Signals used to transmit power long distances must be extremely directive in order to deliver the power at an acceptable efficiency and to prevent excess power from interfering with other RF technology. Phased array antennas offer one method of increasing the directivity of a transmitted beam through off-axis cancellation from the multi-antenna source. Besides beamforming, another focus of this work is on the equations used to describe the efficiency and far field distance of transmitting antennas. Most previously used equations, including the Friis equation and the Goubau equation, are formed by examining singleton antennas, and do not account for the unique properties of antenna arrays. Updated equations and evaluation methods are presented both for the far field and the efficiency of phased array antennas. Experimental results corroborate the far field model and efficiency equation presented, and the implications of these results regarding space solar power and other applications are discussed. The results of this thesis are important to the applications of WPT previously mentioned, and can also be used as a starting point for further WPT and SSP research, especially when looking at the foundations of PAA technology.
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Book chapters on the topic "Far-field directivity"

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ASSAAD, Jamal, Christian BRUNEEL, Jean-Noël DECARPIGNY, and Bertrand DUBUS. "Far-field Directivity Patterns For (YZw)36° Lithium Niobate Bars." In Ultrasonics International 93, 415–18. Elsevier, 1993. http://dx.doi.org/10.1016/b978-0-7506-1877-9.50103-7.

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Conference papers on the topic "Far-field directivity"

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Wu, Bae-Ian. "Limitation on far-field super directivity using transformation optics." In 2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium). IEEE, 2013. http://dx.doi.org/10.1109/usnc-ursi.2013.6715470.

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Simms, S. W., and V. F. Fusco. "Far field directivity enhancement using modified artificial magnetic conductor." In IET Seminar on Metameterials for Microwave and (Sub) Millimetrewave Applications: Electromagnetic Bandgap and Double Negative Designs, Structures, Devices and Experimental Validation. IEE, 2006. http://dx.doi.org/10.1049/ic:20060394.

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Ana-Maria, Chiselev, Moraru Luminita, Onose Laura, Madalin Bunoiu, and Iosif Malaescu. "Study of Far—Field Directivity Pattern for Linear Arrays." In PHYSICS CONFERENCE TIM-10. AIP, 2011. http://dx.doi.org/10.1063/1.3647085.

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Assaad, Jamal, Christian Bruneel, Jean-Michel Rouvaen, and Régis Bossut. "An Extrapolation Method to Compute Far-Field Pressures From Near-Field Pressures Obtained by Finite Element Method." In ASME 1995 Design Engineering Technical Conferences collocated with the ASME 1995 15th International Computers in Engineering Conference and the ASME 1995 9th Annual Engineering Database Symposium. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/detc1995-0406.

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Abstract The finite element method is widely used for the modeling of piezoelectric transducers. With respect to the radiation loading, the fluid is meshed and terminated by an external nonreflecting surface. This reflecting surface can be made up with dipolar damping elements that absorb approximately the outgoing acoustic wave. In fact, with dipolar dampers the fluid mesh can be quite limited. This method can provides a direct computation of the near-field pressure inside the selected external boundary. This paper describes an original extrapolation method to compute far-field pressures from near-field pressures in the two-dimensional (2-D) case. In fact, using the 2-D Helmholtz equation and its solution obeying the Sommerfeld radiation condition, the far-field directivity pattern can be expressed in terms of the near-field directivity pattern. These developments are valid for any radiation problem in 2D. One test example is described which consists of a finite width planar source mounted in a rigid or a soft baffle. Experimental results concerning the far-field directivity pattern of lithium niobate bars (Y-cut) are also presented.
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Lowis, Christopher, Phillip Joseph, and Andrew Kempton. "An In-duct Beamformer For The Estimation Of Far-field Directivity." In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference). Reston, Virigina: American Institute of Aeronautics and Astronautics, 2008. http://dx.doi.org/10.2514/6.2008-2859.

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Tester, Brian, and Luigi De Mercato. "Far-field directivity of rotor-alone tones radiated from fan intakes with spliced liners for different intake shapes, with flow." In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference). Reston, Virigina: American Institute of Aeronautics and Astronautics, 2006. http://dx.doi.org/10.2514/6.2006-2456.

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Harne, Ryan L., and Danielle T. Lynd. "Acoustic Beamfolding With a Miura-Ori Tessellated Transducer Array." In ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-59907.

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Vibrating structures radiate acoustic waves into the fluid media which surround them at the structure-fluid interface. Fundamentally, the interfacing structural surface topology governs the amplitude and frequency sensitivities of acoustic energy propagation away from the surface, a characteristic known as directivity. Assembling many planar acoustic transducer elements into arrays is one way to greatly enhance the far-field energy propagation directional sensitivities. Due to the spatially distributed transducers, the travelling waves combine uniquely in phase at an observation point in the far field where large energy focusing or suppressing occurs as a function of the spatial coordinates. The conventional approach to tune planar array directivity for a different purpose or new spectral sensitivity is to actively adjust each array input signal with a controlled phase delay which requires accessory hardware and computational burden. From a different standpoint, structures created from foldable, tessellated architectures, such as origami patterns, can yield enormous topological variation from the simple, kinematic motions of connected planar facets. This observation has inspired recent efforts to develop innovative, adaptable engineering systems using origami tessellations as an architectural basis for design. Considering together the topological sensitivities of planar acoustic arrays and the multifunctionality engendered by folding origami-based structures having planar facets, this research seeks to surmount the limitations of conventional acoustic arrays and explore a new idea for adaptable acoustic systems by integrating principles from acoustics and origami-inspired design. Upon the new idea, this research studies a tessellated acoustic transducer array able to drastically adapt energy guiding capabilities through simple topological folding. An array based on the Miura-ori folding pattern is examined in a new structural-acoustic model to assess the capability of folding to tune the magnitude and spatial variations of acoustic energy propagated to the far field. The acoustic directivity of the array is found to exhibit massive sensitivities based on the excitation frequency and fold angle, giving rise to large amplitude and spatial adaptation of the energy guiding to the far field point. An experimental tessellated acoustic array is fabricated and evaluated to verify the trends predicted by the model. From the measurements, it is conclusively seen that the topological change of the origami-inspired acoustic array empowers straightforward and reversible means for orders of magnitude in change in acoustic energy transmission and steering. Upon this basis, future compact, deployable, and kinematically-adaptable wave energy transmission systems may be developed for applications including field imaging, communications, and long range force projection.
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Li, Ang, Jun Chen, Yangfan Liu, J. Stuart Bolton, and Patricia Davies. "Noise Source Identification and Noise Directivity Analysis of Bladeless Fans by Combined CFD and CAA Method." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20168.

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Abstract The bladeless fan is a new concept of fan that does not have visible impellers. It features low noise level, uniform airflow, and improved safety. It has been widely applied in household appliances. Since the customers are particularly sensitive to the noise generated by the fan, the aeroacoustics performance of the fan needs to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the aeroacoustics performance and identify the major noise source of the bladeless fan. A prototype of the bladeless fan, including a wind channel, a base cavity, a rotor and a stator inside the base, is set in a computational domain of 4m × 2m × 2m and the airflow through the fan is simulated. The hybrid mesh is generated, the unstructured mesh in the near field, and the structured at the far field. To compute the flow field, steady RANS simulation (standard k–ε turbulence model) and Large Eddy simulation (Smagorinsky-Lilly model) are carried out. Ffowcs Williams and Hawkings (FW-H) analogy is used to predict the acoustic field. Experiments, including air velocity measurement and sound pressure measurement, are conducted to validate simulation results. Sound pressure level results at the near-field receiver illustrate that the blade passage frequency can be captured by combined CFD and CAA method. Noise source analysis shows that the combination of the rotor and stator contributes most to the noise produced by the bladeless fan. The wind channel is the secondary source. Sound pressure level contours at different distances and different heights are generated to investigate the directivity pattern of the noise generated by the bladeless fan. At the near field, the produced noise at the front and the back of the bladeless fan are louder than those at left and right; at the far field, the noise at the front is much larger than the other three sides. In addition, at the near field, with the increase of the height, two separated hotspots appear over 2,500Hz and the sound pressure level at these two hotspots increases; at the far field, the noise distribution at different heights is similar and the peak near 3,000Hz can be estimated. A possible reason to cause this peak is vortex shedding at the trailing edge of the rotor’s blades. The aeroacoustics analysis is helpful to develop strategies to reduce noise and guide the improved design of the bladeless fan.
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Mockett, Charles, Marian Fuchs, Felix Kramer, Ulf Michel, Frank Thiele, and Mathias Steger. "Further Development and Initial Validation of Innovative DES-Based Approaches for the Prediction of Jet Noise Installation Effects." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-65253.

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Further development and validation of an innovative DES-based methodology for the prediction of jet noise from installed configurations is presented. A Grey-Area improved Delayed Detached-Eddy Simulation (DDES) model has been implemented in an industrial solver and validated for a static single-stream jet. The measured far-field sound directivity was predicted to within 2 dB and frequencies up to around St = 2 to 3 were resolved on a grid of 15.4M cells. To address the key problem of defining a suitable location of the data surface for Ffowcs Williams & Hawkings (FWH) far-field integration, a sensor function based on a statistical evaluation of the vorticity magnitude is proposed. This is applied to a complex installed jet/wing configuration, for which predicted far-field noise levels are shown. A strong increase in noise due to the presence of the wing of up to 18 dB in the forward arc is reported. This interaction noise becomes stronger and shifts to higher frequencies when the wing is moved closer to the jet.
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Anderson, Jason M., Devin O. Stewart, and William K. Blake. "Experimental Investigations of Sound From Flow Over Rough Surfaces." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11445.

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Turbulent boundary layer flows over rough surfaces are known to produce elevated far-field acoustic sound levels. The nature by which surface irregularities alter the near-field surface pressures and subsequently affect the sound generation to the scattering of high wavenumber convective pressures to low wavenumber acoustic pressures, which is typically interpreted as a dipole-like source. The focus of the current investigation is the experimental interrogation of both near- and far-field pressures due to the flow over roughened surfaces in order to identify the source mechanisms and to validate physical models of roughness sound. For rough surfaces composed of large geometrical elements (defined by large Reynolds numbers based on roughness height and friction velocity), such as hemispheres and cubes, the measured near-field surfaces pressures indicate that the local interstitial flows become important in determining the sound radiation characteristics. In order to describe the aeroacoustic source region, scaling laws are developed for surface pressures at locations around the roughness elements for various roughness configurations and flow speeds. Relationships between surface pressures amongst the rough surface elements and far-field pressures measured at several directional aspects were examined to identify roughness sound source mechanisms. Measurements of a dipole directivity pattern and dipole efficiency factors obtained when normalizing radiated sound by surface pressures offer support to the scattering theories for roughness sound. Using existing pressure scattering models as a basis, an empirical model for roughness sound is generated.
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