Rod H. Self

University of Cambridge, Cambridge, ENG, United Kingdom

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Publications (7)9.37 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. · 1.80 Impact Factor
  • M Azarpeyvand, R H Self
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    ABSTRACT: To calculate the noise emanating from a turbulent flow using an acoustic analogy knowledge concerning the unsteady characteristics of the turbulence is required. Specifically, the form of the turbulent correlation tensor together with various time and length-scales are needed. However, if a Reynolds Averaged Navier-Stores calculation is used as the starting point then one can only obtain steady characteristics of the flow and it is necessary to model the unsteady behavior in some way. While there has been considerable attention given to the correct way to model the form of the correlation tensor less attention has been given to the underlying physics that dictate the proper choice of time-scale. In this paper the authors recognize that there are several time dependent processes occurring within a turbulent flow and propose a new way of obtaining the time-scale. Isothermal single-stream flow jets with Mach numbers 0.75 and 0.90 have been chosen for the present study. The Mani-Gliebe-Balsa-Khavaran method has been used for prediction of noise at different angles, and there is good agreement between the noise predictions and observations. Furthermore, the new time-scale has an inherent frequency dependency that arises naturally from the underlying physics, thus avoiding supplementary mathematical enhancements needed in previous modeling.
    The Journal of the Acoustical Society of America 10/2009; 126(3):1015-25. · 1.65 Impact Factor
  • 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 01/2009; 55(3):433-440. · 0.42 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. · 1.65 Impact Factor
  • Rod H. Self, Mahdi Azarpeyvand
    International Journal of Aeroacoustics 01/2008; 7(2):83-102. · 0.63 Impact Factor
  • R.H Self
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    ABSTRACT: A jet noise source model based on the Lighthill acoustic analogy is presented. Although much of the theory used is well known, a new feature of the model is the inclusion of frequency dependence for the time and length scales used in the turbulence two-point correlation function. It is found that allowing for this experimentally observed dependence markedly improves the agreement of the model's prediction with experimental far-field data. To illustrate this agreement the case of a single turbulent jet is considered. Using well-respected scaling laws for the mean and turbulent properties of such jets a prediction for a single jet noise spectrum is obtained which shows very good agreement with the prediction using the empirically based ESDU database. The effect of altering the frequency dependence of the moving axis timescale is briefly discussed and it is indicated how the source model can be generalized to use RANS and other CFD data to predict jet noise, for single and coaxial jets and also for more novel nozzle geometries.
    Journal of Sound and Vibration 01/2004; · 1.61 Impact Factor
  • Source
    M.J. FISHER, R.H. SELF
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    ABSTRACT: This paper summarizes some highlights of aeroacoustics research in Europe in 2001, compiled from information provided to the Confederation of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC). The CEAS comprises the national Aerospace Societies of France (AAAF), Germany (DGLR), Italy (AIDAA), The Netherlands (NVvL), Spain (AIAE), Sweden (FTF), Switzerland (SVFW) and the United Kingdom (RAeS).
    Journal of Sound and Vibration 01/2002; · 1.61 Impact Factor

Publication Stats

17 Citations
9.37 Total Impact Points

Institutions

  • 2012
    • University of Cambridge
      • Department of Engineering
      Cambridge, ENG, United Kingdom
  • 2009
    • Institute of Sound and Vibration Research
      Southampton, England, United Kingdom
  • 2002–2009
    • University of Southampton
      • Institute of Sound and Vibration Research (ISVR)
      Southampton, England, United Kingdom