Rod Self

University of Southampton, Southampton, England, United Kingdom

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Publications (13)5.51 Total impact

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    ABSTRACT: The effects of multiple scattering on acoustic manipulation of spherical particles using helicoidal Bessel-beams are discussed. A closed-form analytical solution is developed to calculate the acoustic radiation force resulting from a Bessel-beam on an acoustically reflective sphere, in the presence of an adjacent spherical particle, immersed in an unbounded fluid medium. The solution is based on the standard Fourier decomposition method and the effect of multi-scattering is taken into account using the addition theorem for spherical coordinates. Of particular interest here is the investigation of the effects of multiple scattering on the emergence of negative axial forces. To investigate the effects, the radiation force applied on the target particle resulting from a helicoidal Bessel-beam of different azimuthal indexes (m = 1 to 4), at different conical angles, is computed. Results are presented for soft and rigid spheres of various sizes, separated by a finite distance. Results have shown that the emergence of negative force regions is very sensitive to the level of cross-scattering between the particles. It has also been shown that in multiple scattering media, the negative axial force may occur at much smaller conical angles than previously reported for single particles, and that acoustic manipulation of soft spheres in such media may also become possible.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 08/2012; 59(8):1741-9. DOI:10.1109/TUFFC.2012.2378 · 1.51 Impact Factor
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    ABSTRACT: This paper is concerned with the mathematical modelling of sound radiation from a semi-infinite unflanged annular duct due to a monopole acoustically-compact source located inside the duct. The acoustic field inside the duct is modelled using an appropriate Green's function solution and the noise propagation from the duct-exit through the shear layer to farfield is dealt with using a standard Wiener-Hopf solution. Results are presented for far-field noise and modal contribution for observers positioned at different polar angles. The effect of source radial and axial position and its frequency is thoroughly investigated. The effects of jet speed on the appearance of cone of silence and jet blockage at different frequencies are also studies. It is shown that the source position plays an important role on duct modes excitation and therefore far-field noise directivity.
    17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference); 06/2011
  • 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference); 06/2011
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    ABSTRACT: In this work, a numerical investigation of the noise from coplanar coaxial jet flows is conducted by using a new aeroacoustics approach called LRT. This method provides the ability to calculate the refraction effects experienced by the sound waves propagating throughout the jet and evaluate their contribution on the far-field noise predictions. A large number of jet operation conditions and nozzles configurations were investigated aiming to understand the sound propagation effects, sources distributions and far-field noise by coplanar coaxial jet flows. This is the second task of a continuous effort of numerical tests to validate the LRT method as fast noise prediction tool. Experimental data were used to corroborate the predictions of the new method which showed considerably good agreements. This fact suggests that the basic theoretical model is valid and that the model theory contains the essential physics of sound generation and propagation by a high subsonic jet. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.
    17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference); 06/2011
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    ABSTRACT: Formulas for calculating the effect of centerbody scattering on the sound radiated from an advanced open rotor are presented. The effects of blade sweep and distributed blade loading are considered. Mach number effects are also implicitly included in the model. The work extends a previously published method and applies it to a practical situation in which scattering by the centerbody has a significant effect on the radiated sound field. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.
    AIAA Journal 05/2010; 48(5):975-980. DOI:10.2514/1.44659 · 1.21 Impact Factor
  • Michael Kingan · Rod Self
    15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference); 05/2009
  • Rod H. Self · Mahdi Azarpeyvand
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    ABSTRACT: The turbulent energy dissipation rate time-scale and length-scale has been routinely used for the prediction of noise from turbulent flows, particularly jet streams. However, this is not the only possible choice. In general, scales evolving in a turbulent medium are threefold. First, those associated with the mean flow; second, those attributed to the turbulence and the mean flow interactions; and third, scales related to the turbulence-turbulence interactions. In this paper, special attention will be paid to further study of the underlying physics of aerodynamic noise by examining various time-scales. To do so, three time scales, namely, dissipation, production, and strain rate time scales, are defined and used in the source modelling to emphasis the effect of the turbulence structures at different jet regions on the jet noise production mechanism. The required mean value and turbulence parameters are obtained using a modified k − ∈ turbulence model, and Lighthill’s Acoustic Analogy is used for the prediction of the emanated noise.
    Acoustical Physics 05/2009; 55(3):433-440. DOI:10.1134/S106377100903021X · 0.88 Impact Factor
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    ABSTRACT: The location of jet noise sources is a far from trivial problem that is of great importance for both understanding the noise production and radiation mechanisms and also for finding new jet noise reduction strategies. This paper presents comparisons of theoretical results with data for a number of jets. The theory used is based on the MGBK method but including a novel time scale based on the rate of energy transfer through the turbulent cascade. This new technique has been shown to give a number of advantages over existing models. The experimental results were obtained using the Polar Correlation Technique and were made at QinetiQ's Jet Noise Facility in the UK as part of the EU FP6 programme CoJeN. The high resolution jet noise images resulted from using a 64 microphone polar arc array set at two reference angles, namely 60 and 90 degrees to the jet axis. Comparisons with experimental data are made for coplanar and short cowl nozzles at different working conditions for predictions from different theoretical models. It is shown that the best agreement is obtained for the prediction methodology using the energy transfer rate timescale.
    The Journal of the Acoustical Society of America 06/2008; 123(5):3125. DOI:10.1121/1.2933055 · 1.50 Impact Factor
  • 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference); 05/2008
  • Rod H. Self · Mahdi Azarpeyvand
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    ABSTRACT: This paper presents a study of the effects of the form of the time-scale used in aerodynamic noise prediction methodologies with application to the prediction of noise from hot jets. It was motivated by the need to improve the spectral shape of predictions obtained using Lighthill Acoustic Analogy based schemes such as the MGBK method in conjunction with a RANS CFD flow simulation. Acoustic Analogy formulations require knowledge of the unsteady characteristics of the turbulence whereas using a RANS calculation as the starting point provides only steady characteristics of the flow and it is then necessary to model the unsteady behaviour in some way. A critical issue is the proper definition of the acoustic time scale which empirical studies have shown to be frequency dependent. The authors discuss how this dependence arises from the underlying physics of the flow by considering a timescale based on the rate of energy transfer through the turbulent cascade. The technique is applied to noise prediction for both isothermal and heated jets using the MGBK method. It is shown that using the new definition of timescale results in good agreement with experimental measurements in both cases. It is suggested that such a definition will prove robust and find application in other areas of aeroacoustic noise prediction.
    International Journal of Aeroacoustics 04/2008; 7(2):83-102. DOI:10.1260/147547208784649455 · 0.40 Impact Factor
  • 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference); 05/2007
  • Rod Self · Mahdi Azarpeyvand
    13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference); 05/2007
  • 10th AIAA/CEAS Aeroacoustics Conference; 05/2004