Special Issue "Recent Advances in Aeroacoustics"

A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (30 September 2016).

Special Issue Editor

Prof. Dr. Luís M.B.C. Campos

Guest Editor
Center for Aeronautical and Space Science and Technology (CCTAE), IDMEC, Instituto Superior Técnico (IST), Universidade de Lisboa, 1049-001 Lisboa Codex, Portugal.
Interests: aeroacoustics; magnetohydrodynamics; flight dynamics and performance; solar-terrestrial and stellar astrophysics; special functions and differintegration operators
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Special Issue Information

Dear Colleagues,

Aeroacoustics has evolved from being an afterthought of noise reduction measures to become an integral part of the design of aircraft and their engines. The considerable progress in reducing engine noise has led to the increasing relevance of aerodynamic noise, adding another dimension to aeroacoustics. The growth of air traffic, doubling every 15 to 25 years, compounds the challenge of reducing the total noise exposure of near airport residents. The reduction of external noise is the subject of specific performance targets in the aeronautical research programs, such as H2020-Acare in Europe and the Environmentally Responsible Aircraft (ERA) in the U.S. These targets of noise reduction, per aircraft operation, aim at enabling stricter International Civil Aviation Organization (ICAO) noise standards and avoiding noise restrictions imposed by authorities at major airports, in addition to the certification and local standards for external noise. Airlines value low internal noise for the comfort of passengers. The preceding factors all contribute to the increasing breadth and importance of aeroacoustics. The Special Issue addresses this broad change of topics, welcoming papers on: (i) analytical and computational aeroacoustics, (ii) experimental methods, (iii) applications to engine and aircraft design, and (iv) low-noise operating procedures. Particularly desirable are papers connecting more than one of aspects (i) to (iv), e.g., (i) computational aeroacoustics with (ii) experimental validation, simulating an (iii) aircraft application or (iv) operational procedure, possibly as a part of an on-going or recently completed research project.

Prof. Dr. Luís M.B.C. Campos
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Aerospace is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Aeroacoustics
  • airport noise
  • aircraft noise
  • engine noise
  • low-noise operations

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Editorial

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Open AccessEditorial
Recent Advances in Aeroacoustics
Aerospace 2016, 3(4), 40; https://doi.org/10.3390/aerospace3040040 - 23 Nov 2016
Abstract
Acoustics is one of the oldest examples of applied research, long before the term was even coined: [...]
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(This article belongs to the Special Issue Recent Advances in Aeroacoustics)

Research

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Open AccessArticle
Linearized Euler Equations for the Determination of Scattering Matrices for Orifice and Perforated Plate Configurations in the High Mach Number Regime
Aerospace 2016, 3(4), 33; https://doi.org/10.3390/aerospace3040033 - 17 Oct 2016
Cited by 6
Abstract
The interaction of a plane acoustic wave and a sheared flow is numerically investigated for simple orifice and perforated plate configurations in an isolated, non-resonant environment for Mach numbers up to choked conditions in the holes. Analytical derivations found in the literature are [...] Read more.
The interaction of a plane acoustic wave and a sheared flow is numerically investigated for simple orifice and perforated plate configurations in an isolated, non-resonant environment for Mach numbers up to choked conditions in the holes. Analytical derivations found in the literature are not valid in this regime due to restrictions to low Mach numbers and incompressible conditions. To allow for a systematic and detailed parameter study, a low-cost hybrid Computational Fluid Dynamic/Computational Aeroacoustic (CFD/CAA) methodology is used. For the CFD simulations, a standard kϵ Reynolds-Averaged Navier–Stokes (RANS) model is employed, while the CAA simulations are based on frequency space transformed linearized Euler equations (LEE), which are discretized in a stabilized Finite Element method. Simulation times in the order of seconds per frequency allow for a detailed parameter study. From the application of the Multi Microphone Method together with the two-source location procedure, acoustic scattering matrices are calculated and compared to experimental findings showing very good agreement. The scattering properties are presented in the form of scattering matrices for a frequency range of 500–1500 Hz. Full article
(This article belongs to the Special Issue Recent Advances in Aeroacoustics)
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Open AccessArticle
Improved Separation of Tone and Broadband Noise Components from Open Rotor Acoustic Data
Aerospace 2016, 3(3), 29; https://doi.org/10.3390/aerospace3030029 - 20 Sep 2016
Cited by 4
Abstract
The term “open rotor” refers to unducted counter-rotating dual rotors or propellers used for propulsion. The noise generated by an open rotor is very complicated and requires special techniques for its analysis. The determination of its tone and broadband components is vital for [...] Read more.
The term “open rotor” refers to unducted counter-rotating dual rotors or propellers used for propulsion. The noise generated by an open rotor is very complicated and requires special techniques for its analysis. The determination of its tone and broadband components is vital for properly assessing the noise control parameters and also for validating open rotor noise prediction codes. The data analysis technique developed by Sree for processing raw acoustic data of open rotors has been modified to yield much better results of tone and broadband separation particularly for the case when the two rotor speeds are approximately the same. The modified algorithm is found to eliminate most or all of the “spikes” previously observed in the broadband spectra computed from the original algorithm. A full description of the modified algorithm and examples of improved results from its application are presented in this paper. Full article
(This article belongs to the Special Issue Recent Advances in Aeroacoustics)
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Open AccessArticle
Theoretical and Numerical Modeling of Acoustic Metamaterials for Aeroacoustic Applications
Aerospace 2016, 3(2), 15; https://doi.org/10.3390/aerospace3020015 - 26 May 2016
Cited by 12Correction
Abstract
The advent, during the first decade of the 21st century, of the concept of acoustic metamaterial has disclosed an incredible potential of development for breakthrough technologies. Unfortunately, the extension of the same concepts to aeroacoustics has turned out to be not a trivial [...] Read more.
The advent, during the first decade of the 21st century, of the concept of acoustic metamaterial has disclosed an incredible potential of development for breakthrough technologies. Unfortunately, the extension of the same concepts to aeroacoustics has turned out to be not a trivial task, because of the different structure of the governing equations, characterized by the presence of the background aerodynamic convection. Some of the approaches recently introduced to circumvent the problem are biased by a fundamental assumption that makes the actual realization of devices extremely unlikely: the metamaterial should guarantee an adapted background aerodynamic convection in order to modify suitably the acoustic field and obtain the desired effect, thus implying the porosity of the cloaking device. In the present paper, we propose an interpretation of the metamaterial design that removes this unlikely assumption, focusing on the identification of an aerodynamically-impermeable metamaterial capable of reproducing the surface impedance profile required to achieve the desired scattering abatement. The attention is focused on a moving obstacle impinged by an acoustic perturbation induced by a co-moving source. The problem is written in a frame of reference rigidly connected to the moving object to couple the convective wave equation in the hosting medium with the inertially-anisotropic wave operator within the cloak. The problem is recast in an integral form and numerically solved through a boundary-field element method. The matching of the local wave vector is used to derive a convective design of the metamaterial applicable to the specific problem analyzed. Preliminary numerical results obtained under the simplifying assumption of a uniform aerodynamic flow reveal a considerable enhancement of the masking capability of the convected design. The numerical method developed shows a remarkable computational efficiency, completing a simulation of the entire field in a few minutes on mid-end workstations. The results are re-interpreted in term of boundary impedance, assuming a locally-reacting behavior of the outer boundary of the cloaking layer. The formulation is currently being extended to the analysis of arbitrarily complex external flows in order to remove the limitation of the background uniform stream in the host. Full article
(This article belongs to the Special Issue Recent Advances in Aeroacoustics)
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Open AccessArticle
Validation of a Discontinuous Galerkin Implementation of the Time-Domain Linearized Navier–Stokes Equations for Aeroacoustics
Aerospace 2016, 3(1), 7; https://doi.org/10.3390/aerospace3010007 - 17 Feb 2016
Cited by 4
Abstract
The propagation of small perturbations in complex geometries can involve hydrodynamic-acoustic interactions, coupling acoustic waves and vortical modes. A propagation model, based on the linearized Navier–Stokes equations, is proposed. It includes the mechanism responsible for the generation of vorticity associated with the hydrodynamic [...] Read more.
The propagation of small perturbations in complex geometries can involve hydrodynamic-acoustic interactions, coupling acoustic waves and vortical modes. A propagation model, based on the linearized Navier–Stokes equations, is proposed. It includes the mechanism responsible for the generation of vorticity associated with the hydrodynamic modes. The linearized Navier–Stokes equations are discretized in space using a discontinuous Galerkin formulation for unstructured grids. Explicit time integration and non-reflecting boundary conditions are described. The linearized Navier–Stokes (LNS) model is applied to two test cases. The first one is the time-harmonic source line in an incompressible inviscid two-dimensional mean shear flow in an infinite domain. It is shown that the proposed model is able to capture the trailing vorticity field developing behind the mass source and to represent the redistribution of the vorticity. The second test case deals with the analysis of the acoustic propagation of an incoming perturbation inside a circular duct with a sudden area expansion in the presence of a mean flow and the evaluation of its scattering matrix. The computed coefficients of the scattering matrix are compared to experimental data for three different Mach numbers of the mean flow, M0 = 0.08, 0.19 and 0.29. The good agreement with the experimental data shows that the proposed method is suitable for characterizing the acoustic behavior of this kind of network. Full article
(This article belongs to the Special Issue Recent Advances in Aeroacoustics)
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Open AccessArticle
Acoustic Radiation by 3D Vortex Rings in Air
Aerospace 2015, 2(4), 627-636; https://doi.org/10.3390/aerospace2040627 - 06 Nov 2015
Cited by 1
Abstract
Acoustic radiation emitted by three-dimensional (3D) vortex rings in air has been investigated on the basis of the unsteady Navier–Stokes equations. Power series expansions of the unknown functions with respect to the initial vorticity which is supposed to be small are used. In [...] Read more.
Acoustic radiation emitted by three-dimensional (3D) vortex rings in air has been investigated on the basis of the unsteady Navier–Stokes equations. Power series expansions of the unknown functions with respect to the initial vorticity which is supposed to be small are used. In such a manner the system of the Navier–Stokes equations is reduced to a parabolic system with constant coefficients at high derivatives. The initial value problem is as follows. The vorticity is defined inside a toroid at t = 0. Other gas parameters are assumed to be constant throughout the whole space at t = 0. The solution is expressed by multiple integrals which are evaluated with the aid of the Korobov grids. Density oscillations are analyzed. The results show that the frequency band depends on the initial size of the vortex ring and its helicity. The presented data may be applied to the study of a flow in a wake region behind an aerodynamic body. Full article
(This article belongs to the Special Issue Recent Advances in Aeroacoustics)
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