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International Journal of Aeroacoustics
Journal Prestige (SJR): 0.284
Citation Impact (citeScore): 1
Number of Followers: 37  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1475-472X - ISSN (Online) 2048-4003
Published by Sage Publications Homepage  [1175 journals]
  • Guest Editor Biography

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      Pages: 289 - 289
      Abstract: International Journal of Aeroacoustics, Volume 21, Issue 5-7, Page 289-289, September 2022.

      Citation: International Journal of Aeroacoustics
      PubDate: 2022-09-17T02:54:35Z
      DOI: 10.1177/1475472X221112063
      Issue No: Vol. 21, No. 5-7 (2022)
       
  • Editorial

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      Authors: Yueping Guo
      Pages: 290 - 290
      Abstract: International Journal of Aeroacoustics, Volume 21, Issue 5-7, Page 290-290, September 2022.

      Citation: International Journal of Aeroacoustics
      PubDate: 2022-09-17T02:54:25Z
      DOI: 10.1177/1475472X221112056
      Issue No: Vol. 21, No. 5-7 (2022)
       
  • Acoustic energy balances for sound radiated from duct exit with mean flow

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      Authors: Sjoerd W Rienstra
      Pages: 410 - 429
      Abstract: International Journal of Aeroacoustics, Volume 21, Issue 5-7, Page 410-429, September 2022.
      An old model problem for the exchange of energy between sound field and mean flow by vortex shedding has been worked out in numerical detail. The analytically exact solution of the problem of reflection, diffraction and radiation of acoustic modes in a semi-infinite annular duct with uniform subsonic mean flow, including shedding of unsteady vorticity from the duct exit, allows a precise formulation of Myers’ energy for perturbations of an inviscid mean flow. The transmitted power [math] in the duct and the radiated power [math] in the far field differ by the amounts of hydrodynamic far field powers [math] inside and [math] outside the wake (vortex sheet) emanating from the duct edge, plus the power [math] that disappears into the vortex sheet. This last component represents the source term in Myers’ energy equation. This is evidence of the non-conserved character of acoustic energy in mean flow, owing to the coupling of the acoustic field with the mean flow. [math], [math] and [math] are always positive. This is normally the case too for [math] and [math]. But for not too high frequencies or other circumstances where shed vorticity produces more sound than was necessary for its creation, [math] and even [math] may also be negative.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-09-17T02:54:36Z
      DOI: 10.1177/1475472X221107363
      Issue No: Vol. 21, No. 5-7 (2022)
       
  • Aerodynamic noise characteristics of non-circular cylinders in subcritical
           flow regime

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      Authors: Arun MG, Sarvoththama Jothi TJ
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      The present study experimentally investigates the aerodynamic noise from the flow around cylinders of square and equilateral triangle cross-sections at different angles of incidence (α). The cylinder models have a side dimension of 10 mm and a span of 300 mm. The free stream velocity (U0) is in the range of 12–36 m/s, and the corresponding Reynolds numbers are 7.8 × 103 to 2.3 × 104, which is in the subcritical flow regime. The characteristic acoustic tones are generated at α = 30° and 45° for square and triangular cylinders. The frequency of acoustic tones linearly increases with the free stream velocity, and the corresponding Strouhal numbers are found to be in the range of 0.13–0.16. Depending on the angle of incidence, the overall sound pressure level is higher than the background noise by 4–24 dB for the square cylinder and 3–15 dB for the triangular cylinder at U0 = 36 m/s. The highest noise level of the square cylinder is 90 dB at α = 45° and 79 dB at α = 30° for the triangular cylinder. The spectral scaling with the sixth power of the free stream velocity indicates the dipole behaviour of the acoustic tones. The mean and root-mean-square velocity profiles in the wake region characterise the noise emissions at different angles of incidence. The comparative acoustic study of the non-circular cylinders with a circular counterpart showed that the highest noise level is from the square cylinder at α = 45°. The directivity study shows that the noise level of the square cylinder at α = 45° at 90° angular location (θ) is higher by 6.5 dB than that at θ = 30°.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-11-15T05:35:57Z
      DOI: 10.1177/1475472X221140869
       
  • Data-driven neural networks for source localization and reconstruction
           using a planar array

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      Authors: Sai Manikanta Kaja, Srinath Srinivasan, S. K. Chaitanya, K. Srinivasan
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      This study uses specialized deep neural networks comprising dense and convolutional neural networks to localize noise sources and reconstruct acoustic data on a reconstruction plane. The networks are trained on simulated acoustic data free from any form of noise in the signal. It is observed that neural networks can effectively localize monopole and dipole sources and reconstruct the acoustic data in reconstruction planes with higher accuracy than conventional methods. Performance of the networks is consistent over changes in some parameters like the source strength, noise in the input signal, and frequency range. Various tests are performed to assess the individual network performance. Results indicate that neural networks trained on a subset of the data are effective over the entire data set without significant bias or variance. Errors as low as 1% are observed, and the maximum error observed is below 5%. While reconstruction error decreased with an increase in the frequency of monopole sources, it increased with an increase in frequency for dipole sources.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-11-11T12:29:22Z
      DOI: 10.1177/1475472X221136884
       
  • Numerical study on the noise propagation characteristics of rotor in
           non-uniform downwash flowfield Based on Linearized Euler Equations

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      Authors: Tao Yang, Xi Chen, Qijun Zhao, Guoqing Zhao
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      To study the influence of non-uniform flowfield on the propagation characteristics of helicopter rotor noise, a Hybrid Computational Aeroacoustics (HCAA) method is developed. The acoustic source region is simulated by Computational Fluid Dynamics (CFD) technique with the Unsteady Reynolds Averaged Navier-Stokes equations (URANS) as the governing equations. Acoustic near-field is simulated by Computational Aeroacoustics (CAA) technique with the Linearized Euler Equations (LEE) as the governing equations, and the numerical discretization of the LEE is accomplished by Runge-Kutta Discontinuous Galerkin (RKDG) method. A novel acoustic source extraction method based on pressure and pressure gradient is proposed to accomplish the one-way CFD-CAA weak coupling. The HCAA method is validated through comparisons with noise experimental data of the UH-1H model rotor and the BO-105 model rotor. Based on the proposed HCAA method, the convection and refraction effects of rotor noise under different collective pitch angles are analyzed. The results show that the distortion effect of the rotor noise is most affected by the non-uniformly distributed downwash velocity field, resulting in an increment of acoustic energy below the rotor plane. The effect of non-uniformly distributed downwash velocity on noise propagation increases with the increase of the collective pitch angle. For the UH-1H model rotor, the maximum change of the sound pressure level is 0.8 dB (about 10% change of the effective sound pressure).
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-11-09T09:46:59Z
      DOI: 10.1177/1475472X221136883
       
  • Reduction of noise generated by cylinder-airfoil interaction using grooved
           structures on the upstream cylinder

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      Authors: Chengchun Zhang, Xiaowei Sun, Tianyu Du, Chun Shen, Zhengwu Chen, Dong Liang, Jiale Zhao, Yingchao Zhang
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      The cylinder-airfoil interaction noise can be reduced by changing the shape of the leading edge of the downstream airfoil. Generally, this way not only can reduce the interaction noise at middle and high frequency, but also can change the peak noise at the low frequency. This study attempts to affect the cylinder-airfoil interaction noise from the perspective of reducing the intensity of the upstream wake shedding vortex. In order to achieve this target, the equally spaced grooves were cut into the upstream cylinder, and the acoustic wind tunnel tests at various incoming velocities (20–60m·s−1) were conducted to compare the interaction noise of cylinder-airfoil (NACA0012) models. It is found that the grooved structure can effectively reduce the peak noise at characteristic frequencies bellow 1000 Hz and the broadband noise in the mid-frequency ranging from 1000 Hz to 3000 Hz, especially for the higher incoming velocity. Thereinto, the peak noise and overall sound pressure level (OASPL) with the grooved cylinder are reduced by 13 dB and 7.2 dB, respectively at the incoming velocity of 60 m·s−1. The numerical simulations based on the large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) acoustic analogy were performed to further reveal the mechanisms of noise reduction when the velocity is 60 m·s−1. The results show that the vortex shedding from cylinder wake is suppressed by the grooved cylinder and the vortex structure at the leading edge of the airfoil is also cut into the small-scale vortex structures by the grooved structure. The pressure fluctuation amplitude and the peak value turbulent kinetic energy in the wake of the grooved cylinder are significantly reduced. In addition, the further spectrum analysis reveals that the weak correlation of the vortex shedding on the grooved cylinder could lead to the suppression of the pressure fluctuation in the cylinder wake, and thereby the interaction noise is significantly reduced.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-10-29T02:15:16Z
      DOI: 10.1177/1475472X221136885
       
  • Jet noise sources for chevron nozzles in under-expanded condition

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      Authors: Hasan Kamliya Jawahar, Stefano Meloni, Roberto Camussi
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      Imperfectly expanded jet flows are known to have additional noise sources known as Screech and broadband shock-associated noise. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock cell structures. In this study, thorough experimental investigations were carried out on chevron nozzles to assess the importance of chevron parameters such as the chevron count and chevron penetration angle on the pressure field emitted by the jet. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as pressure spectra, directivity and overall sound pressure levels along with near-field measurements were acquired for jet Mach numbers ranging from M = 1.1–1.4. Fourier-based and Wavelet-based analyses were used to highlight the different features of the various tested nozzles. Wavelet decomposition results highlight that the presence of the chevrons reduce the acoustic noise especially at a higher axial distance with increased levels of noise reduction achieved by chevron nozzle with deep penetration angle.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-21T06:18:18Z
      DOI: 10.1177/1475472X221101766
       
  • Corrigendum to The effect of the convective momentum transfer on the
           acoustic boundary condition of perforated liners with grazing mean flow

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      Abstract: International Journal of Aeroacoustics, Ahead of Print.

      Citation: International Journal of Aeroacoustics
      PubDate: 2022-04-12T03:00:03Z
      DOI: 10.1177/1475472X221096743
       
  • Professor John Eirwyn Ffowcs Williams FREng: Engineer, educator,
           researcher and entrepreneur, Cambridge Professor and Master of Emmanuel
           College 25 May 1935–12 December 2020

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      Authors: Ann P Dowling
      First page: 291
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      I first met Shôn in October 1973. I had just started Part III of the Cambridge Mathematical Tripos – a post-graduate course that was retrospectively awarded a Masters’ Degree in Mathematics. After a summer job working with Ted Broadbent on aircraft noise at the Royal Aircraft Establishment in Farnborough, I had decided do a PhD in Aeroacoustics. I asked Sir James Lighthill for advice and he told me that he was now focused on biomechanics but a new professor had recently arrived in the Cambridge Department of Engineering and that I should ask him. I made contact with Shôn, saw him in his office that afternoon, and he agreed to supervise me for a PhD. As quickly and simply as that, I was on a path that for me was transformational, not only an exciting research future, but the start of my transition from mathematics into engineering. Throughout my career, Shôn continued to be a major influence on me as he has for many others.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-13T05:12:24Z
      DOI: 10.1177/1475472X221107356
       
  • Reminiscing about Prof. John E. Ffowcs Williams

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      Authors: Anjaneyulu Krothapalli
      First page: 307
      Abstract: International Journal of Aeroacoustics, Ahead of Print.

      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-12T06:42:44Z
      DOI: 10.1177/1475472X221107373
       
  • Challenges and opportunities for low noise electric aircraft

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      Authors: Eric Greenwood, Kenneth S Brentner, Robert F Rau, Ze Feng Ted Gan
      First page: 315
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      A new class of electric aircraft is being developed to transport people and goods as a part of the urban and regional transportation infrastructure. To gain public acceptance of these operations, these aircraft need to be much quieter than conventional airplanes and helicopters. This article seeks to review and summarize the aeroacoustic research relevant to this new category of aircraft. First, a brief review of the history of electric aircraft is provided, with an emphasis on how these aircraft differ from conventional aircraft. Next, the physics of rotor noise generation are reviewed, and the noise sources most likely to be of concern for electric aircraft are highlighted. These are divided into deterministic and nondeterministic sources of noise. Deterministic noise is expected to be dominated by the unsteady loading noise caused by the aerodynamic interactions between components. Nondeterministic noise will be generated by the interaction of the rotor or propeller blades with turbulence from ingested wakes, the atmosphere, and self-generated in the boundary layer. The literature for these noise sources is reviewed with a focus on applicability to electric aircraft. Challenges faced by the aeroacoustician in understanding the noise generation of electric aircraft are then identified, as well as the new opportunities for the prediction and reduction of electric aircraft noise that may be enabled by advances in computational aeroacoustics, flight simulation, and autonomy.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-28T06:01:08Z
      DOI: 10.1177/1475472X221107377
       
  • Acoustic transmission loss and noise from Kevlar wind tunnel walls

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      Authors: Stewart Glegg, Máté Szőke, William Devenport
      First page: 382
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      In this paper we will develop a model for the acoustic transmission loss and self-noise generated by a Kevlar wind tunnel wall. It is shown that the porosity of the fabric is the most important controlling factor of the transmission loss, and the effect of wind tunnel flow speed is to increase the losses, as observed in experiments. In addition, a model is developed for the weave noise generated by a Kevlar wind tunnel wall, which is found to be caused by the pumping of the fluid through the pores in the Kevlar and depends on their open area ratio. The mechanism for this sound generation is similar to the roughness noise mechanism for a turbulent boundary layer in that the pore spacing couples with the small wavelength disturbances in the boundary layer to cause acoustic radiation at the sum and difference frequencies.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-07-11T04:47:54Z
      DOI: 10.1177/1475472X221107497
       
  • Self active cancellation of fan noise

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      Authors: Christopher R Fuller
      First page: 430
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      IReduction of fan noise is an important problem in the successful deployment of drones and UAV's. This paper considers a new approach to reducing fan and propeller noise based upon micro vibrations of the propeller blades around their axis of support. Experimental testing was carried out on a five bladed fan arrangement. The micro fan blade vibrations are induced with a pitch link actuator arrangement driven by an electromagnetic actuator. When used in conjunction with a digital feedforward active noise controller, the micro blade vibrations were found to provide global attenuations of fan radiated sound the order of 5 to 10dB of the first few fan tones. The level of required vibrations and the associated electrical power required for the cancelling micro vibrations was shown to be very small compared to the fan motor power requirements. The results demonstrate that the innovative approach, termed “self active cancellation of fan noise”, has good potential for global reduction of fan and propeller noise.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-10T11:20:38Z
      DOI: 10.1177/1475472X221107543
       
  • Leveraging large eddy simulations to assess noise source imaging of a
           controlled supersonic jet

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      Authors: Chitrarth Prasad, Scott Hromisin, Philip J Morris
      First page: 438
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      Noise source imaging based on phased array measurements is an essential tool in the aeroacoustic analysis of new nozzle designs, especially at full-scale. This investigation aims to assess the capability of a deconvolution-based beamforming technique to accurately estimate the changes in noise sources for model-scale heated military jets when fluid inserts are used for noise control. This goal is achieved by performing well-validated Large Eddy Simulations (LES) to complement the experimental measurements. The LES data is segregated into its hydrodynamic, acoustic and thermal components using Doak’s Momentum Potential Theory (MPT). The near-field MPT-derived components are subjected to Spectral Proper Orthogonal Decomposition (SPOD) to compare with the frequency-dependent noise source maps obtained directly from experiments. It is shown that fluid inserts alter the naturally occurring Kelvin-Helmholtz (K-H) instability in the jet shear layer, which leads to a change in the directivity of the noise radiated in the near-field. The upstream shift in the noise source distribution resulting from the modified K-H instability is accurately captured by the deconvolution-based source imaging technique using just the far-field measurements. These changes in source locations as a function of frequency are documented.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-23T07:10:05Z
      DOI: 10.1177/1475472X221107359
       
  • Ffowcs Williams – Hawkings analogy for near-field acoustic sources
           analysis

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      Authors: Alexander Karakulev, Tatiana Kozubskaya, Gleb Plaksin, Ivan Sofronov
      First page: 457
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      The paper expands the scope of applying the Ffowcs Williams – Hawkings integration method. We propose using the acoustic field generated from time-dependent data stored on the FW-H control surface as the same common field for computational acoustic beamforming and dynamic mode decomposition methods to analyze the aerodynamic noise sources. We exemplify that it leads to obtaining mutually consistent and complementary information for reliable prediction of acoustic sources characteristics in the process of inverting data produced by a CFD simulation. Moreover, as the results of applying computational acoustic beamforming and dynamic mode decomposition methods depend on many geometric and algorithmic inputs, the proposed approach makes it possible to use various sets of the latter for a comprehensive analysis of obtained inversions and to form the final answer by an averaging procedure. We illustrate this by taking advantage of fast generating the examined acoustic field snapshots in any required region by the FW-H integration method for the recently developed new inverse computational acoustic beamforming algorithm and the standard dynamic mode decomposition method when carrying out a sensitivity study of the predicted acoustic source. The capabilities of the developed approach are demonstrated on the data of CFD scale-resolving simulation of turbulent flow over the 30P30N high-lift configuration.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-12T07:46:43Z
      DOI: 10.1177/1475472X221107367
       
  • Airframe noise predictions using the Ffowcs Williams-Hawkings equation

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      Authors: David P Lockard
      First page: 476
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      This paper considers potential sources of error when using the Ffowcs Williams-Hawkings equation to make predictions of airframe noise, which entails a relatively low-speed, uniform incoming flow encountering geometry of varying complexity. Numerical simulations are used to investigate several model problems where Ffowcs Williams-Hawkings integration surfaces are placed on solid surfaces as well as in the flow. Comparisons with the pressure obtained directly from the simulations reveal that when solid surfaces are used, the acoustic calculations can produce erroneous results in upstream directions and when scattering bodies block the line of sight from observers to the source. Using solid surface input data implies ignoring all volumetric source effects, which include noise generation as well as flow effects. Nonuniform flow alone, such as is found in a steady boundary layer, was not found to be a significant source of error, so the amplitude and phase changes induced by turbulent eddies in massively separated flow regions is speculated to be the primary cause of the error.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-07-04T06:00:08Z
      DOI: 10.1177/1475472X221107366
       
  • Extension of the concept of Ffowcs-Williams and Hawkings type wave
           extrapolation to non-trivial flow effects and exterior surfaces

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      Authors: Jan Werner Delfs, Michael Mößner, Stanislav Proskurov, Roland Ewert
      First page: 501
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      In appreciation of Ffowcs-Williams and Hawkings’ seminal contribution on describing the sound radiation from moving objects, this article discusses a concept of taking into account local non-trivial flow effects on the sound propagation. The approach is motivated by the fact that the numerical simulation of the sound propagation from complete full scale aircraft by means of volume-discretizing (CAA = Computational AeroAcoustics) methods is prohibitively expensive. In fact, a homogeneous use of such CAA approach would waste computational resources since for low speed conditions the sound propagation around the aircraft is subject to very mild flow effects almost everywhere and may be treated by more inexpensive methods. The part of the domain, where the sound propagation is subject to strong flow effects and thus requiring the use of CAA is quite restricted. These circumstances may be exploited given a consistent coupling of methods.The proposed concept is based on the strong (alternatively weak) coupling of a volume discretizing solver for the Acoustic Perturbation Equations (APE) and a modified Ffowcs-Williams and Hawkings (FW-H) type acoustic integral. The approach is established in the frequency domain and requires two basic ingredients, namely a) a volume discretizing solver for the APE, or for Möhring-Howe’s aeroacoustic analogy, to take into account strong non trivial flow effects like refraction at shear flows wherever necessary, and b) an aeroacoustic integral equation for the propagation part in areas where non-potential mean flow effects are negligible. The coupling of this aeroacoustic integral and the APE solver may be realized in a strong (i.e. two-ways) form in which both components feed back information into one another, or in a weak form (i.e. one-way), in which the sound field output data from the APE solver serves as given input for the integral equation. If an aircraft geometry has minor influence on the sound radiation to arbitrary observer positions, the aeroacoustic integrals may simply be evaluated explicitly. If on the other hand, the presence of the geometry has an important influence on the sound radiation, then the acoustic integral equation is implicit and requires some sort of numerical solution, in this case a Fast Multipole Boundary Element solver. While conceptually the weak coupling follows the spirit of the FW-H approach to describe sound propagation from aeroacoustic sources the underlying aeroacoustic integral is not based on Lighthill’s analogy, but the aeroacoustic analogy of Möhring-Howe. This is a consequence of the fact that in the two way-coupling the acoustic particle velocity in a moving medium needs to be determined, which is non-trivial based on an acoustic integral. As an important feature of the strong coupling the acoustic integral also provides practically perfect non-reflection boundary conditions even when the desireably small CAA domain does not extend into the far field. The validity of the presented computation approach is demonstrated in two example use cases.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-09-01T04:09:57Z
      DOI: 10.1177/1475472X221107365
       
  • Sound generated by axisymmetric non-plane entropy waves passing through
           flow contractions

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      Authors: Dong Yang, Juan Guzmán-Iñigo, Aimee S. Morgans
      First page: 521
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      For a single-component perfect gas, entropy perturbations are associated with the difference between the overall density fluctuation and that coming from the acoustic perturbation. Entropy perturbations can generate sound when accelerated/decelerated by a non-uniform flow and this is highly relevant to thermoacoustic instabilities for gas turbines and rocket engines, and to noise emission for aero-engines. Widely used theories to model this entropy-generated sound rely on quasi-1D assumptions for which questions of validity were raised recently from both numerical and experimental studies. In the present work, we build upon an acoustic analogy theory for this problem. This theory was initiated by Morfey (J. Sound Vib. 1973) and Ffowcs Williams and Howe (J. Fluid Mech. 1975) about 50 years ago and extended recently by Yang, Guzmán-Iñigo and Morgans (J. Fluid Mech. 2020) to study the effect of non-plane entropy waves at the inlet of a flow contraction on its sound generation. Comparisons against both numerical simulations and previous theory are performed to validate the results.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-23T01:34:09Z
      DOI: 10.1177/1475472X221107368
       
  • Subsonic jet noise source location as a function of nozzle exit boundary
           layer

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      Authors: Nick P Breen, Krish K Ahuja
      First page: 537
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      Over the years, there have been numerous studies on determining subsonic jet noise source locations, typically plotted as Strouhal number as a function of distance from the nozzle exit. A comparison of the results of various studies yields a spread of about two nozzle diameters in measured source location. This work examines how boundary layer thickness, which can vary from nozzle to nozzle, could be the cause of observed differences in different studies in subsonic jet noise source location. Source location measurements of unheated jets from ASME nozzles, which have comparably thinner nozzle exit boundary layers, and conical nozzles, which have comparably thicker nozzle exit boundary layers, are compared. These results are substantiated with the use of schlieren flow visualization and velocity profile measurements. It is found that the nozzles with thinner nozzle exit boundary layers have noise source distributions that are 0.25–2 diameters upstream of those with thicker nozzle exit boundary layers. Thinner nozzle exit boundary layers result in higher growth rates of instability waves, increasing mixing and thereby moving noise sources upstream.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-08T01:01:32Z
      DOI: 10.1177/1475472X221107370
       
  • Systematic validation of the PAAShA shielding prediction method

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      Authors: Russell H Thomas, Yueping Guo
      First page: 558
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      Based on classical diffraction theories with modifications and extensions in analytical formulations and numerical implementations, a new code has been developed at NASA for the prediction of aircraft noise shielding, named as Propulsion Airframe Aeroacoustic Shielding Attenuation (PAAShA). The code is developed primarily for aircraft system noise predictions, although it may also be useable in other applications with acoustic shielding. The requirements for this code are driven by the need for a robust, capable code to use with NASA’s Aircraft Noise Prediction Program (ANOPP) for aircraft integration and system noise research. The requirements are met and include capabilities to use a wide range of aircraft geometries, rapid calculation times consistent with aircraft system noise problems, and the flexibility to model realistic noise source characteristics and distributions. The accuracy and robustness of the method are demonstrated in this paper with a set of problems, including a cylinder, a finite plate, a symmetrical two-dimensional airfoil, and a full three-dimensional hybrid wing body aircraft model tested in a wind tunnel. This range of problems demonstrates both smooth and sharp edge diffraction capabilities for a wide range of frequencies and low Mach number flow effects at low angles of attack. Predictions are shown to be accurate to within 1–4 dB over a wide range of the most significant frequencies and directivity angles. This is determined by comparing with data, which have experimental uncertainties, particularly at high frequencies, high angles, and source characteristics. The accuracy diminishes for geometries that include a significant reflection component, which is not calculated by the code. Accuracy can also be somewhat diminished for high azimuthal angles. Accurate modeling of the noise source, particularly its frequency and directivity characteristics, is essential to obtaining accurate results.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-10T02:03:01Z
      DOI: 10.1177/1475472X221107369
       
  • Acoustic versus aerodynamic installation effects on a generic
           propeller-driven flying architecture

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      Authors: Michel Roger, Daniel Acevedo-Giraldo, Marc C Jacob
      First page: 585
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      The present work addresses the combined aerodynamic and acoustic installation effects observed as a subsonic propeller is partly crossing the near-wake of a wing. Only the tonal noise at multiples of the blade passing frequency is considered. The aerodynamic effect is the onset of additional sound sources caused by blade-wake interaction, compared to the case of the isolated propeller. The acoustic effect is the scattering by the wing. The work is aimed at demonstrating the ability of analytical models to estimate separately these effects, which is of primary interest for the preliminary design steps of a system. A basic experiment carried out in an anechoic, open-jet facility, is described, for validation purposes. The far-field sound measurements are compared to the predictions and some key outcomes are presented. In particular, the model provides guidelines to avoid configurations of excessive noise.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-07-02T05:54:19Z
      DOI: 10.1177/1475472X221107372
       
  • Computationally efficient, frequency-domain quadrupole corrections for the
           Ffowcs Williams and Hawkings equation

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      Authors: Tomoaki Ikeda, Kazuomi Yamamoto
      First page: 610
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      In the present article, frequency-domain formulations of quadrupole corrections are derived in a computationally efficient form for the Ffowcs Williams and Hawkings (FW-H) equation with permeable control surfaces. Quadrupole corrections effectively reduce spurious noise associated with hydrodynamic fluctuations passing across integral surfaces, originally derived for Formulation 1A of Farassat in the time domain. When a corresponding frequency-domain formulation is sought, however, difficulty arises as its Green’s function is written in a convective form and different from that of Formulation 1A. First, the mathematical framework of the convective FW-H equation is shown to be equivalent to Formulation 1A by applying a simple Galilean transformation for rectilinear motion. Then, a frequency-domain formulation is derived via a Fourier transform applied directly to the time-domain quadrupole correction forms. The results of the derived formulation agree precisely with the time-domain solutions, in the verification study of vortex convection, as well as non-uniform entropy convection, in which spurious noise can be effectively removed by the present quadrupole correction integrals.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-07-05T10:26:40Z
      DOI: 10.1177/1475472X221107374
       
  • Role of nozzle-exit boundary layer in producing jet noise

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      Authors: Aharon Z Karon, Krishan K Ahuja
      First page: 626
      Abstract: International Journal of Aeroacoustics, Ahead of Print.
      Often the measurements from different jet noise studies, which are thought to have been acquired at or corrected to identical jet conditions, do not match when compared to each other. This study looks at the nozzle-exit boundary layer as a possible factor for these differences. The nozzle-exit boundary layer state can easily be changed depending on the design of the jet-facility or the nozzle. To this end, jet noise measurements and nozzle-exit velocity profile measurements were acquired for nozzles where the nozzle-exit boundary state was changed either by using different types of nozzles, ASME nozzles versus conical nozzles, or extensions were added to the nozzles straight section. It is shown that as the laminar boundary layer transitions to turbulent, the high-frequency jet noise is reduced. In addition, development of a novel empirical correction for these effects was attempted.
      Citation: International Journal of Aeroacoustics
      PubDate: 2022-06-15T01:45:43Z
      DOI: 10.1177/1475472X221107375
       
 
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