Rod Self

University of Southampton, Southampton, England, United Kingdom

Are you Rod Self?

Claim your profile

Publications (14)5.51 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a complex ray-tracing tool for the calculation of high-frequency Green's functions in 3D mean field jet flows. For a generic problem, the ray solution suffers from three main deficiencies: multiplicity of solutions, singularities at caustics, and the determining of complex solutions. The purpose of this paper is to generalize, combine and apply existing stationary media methods to moving media scenarios. Multiplicities are dealt with using an equivalent two-point boundary-value problem, whilst non-uniformities at caustics are corrected using diffraction catastrophes. Complex rays are found using a combination of imaginary perturbations, an assumption of caustic stability, and analytic continuation of the receiver curve. To demonstrate this method, the ray tool is compared against a high-frequency modal solution of Lilley's equation for an off-axis point source. This solution is representative of high-frequency source positions in real jets and is rich in caustic structures. A full utilization of the ray tool is shown to provide excellent results.
    No preview · Conference Paper · Jun 2014
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Aug 2012 · IEEE transactions on ultrasonics, ferroelectrics, and frequency control
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper reports an extensive near- and far-field analysis of the noise generated by an isothermal, subsonic, circular jet in the presence of a solid, flat plate shield. Far-field polar and azimuthal acoustic images are presented initially to characterize the interaction noise source. Near-field streamwise microphone phase analysis along the plate trailing edge reveals a deeper understanding of the link between the jet hydrodynamic field (both linear and non-linear regions) and the mechanisms behind interaction noise generation. Near-field point spectrum data have also been used successfully to validate Amiet's far-field trailing edge dipole prediction code for low-speed jet acoustic Mach numbers. © 2011 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc.
    No preview · Conference Paper · Jun 2011
  • [Show abstract] [Hide abstract]
    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.
    No preview · Conference Paper · Jun 2011
  • [Show abstract] [Hide abstract]
    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.
    No preview · Conference Paper · Jun 2011
  • Source
    [Show abstract] [Hide abstract]
    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.
    Preview · Article · May 2010 · AIAA Journal
  • Michael Kingan · Rod Self
    [Show abstract] [Hide abstract]
    ABSTRACT: Counter-rotation propeller tip vortex interaction noise occurs when tip vortices, shed from each of the upstream propeller blades, interact with the blades on the downstream propeller. This paper describes two separate models for calculating the noise produced by this interaction. The first model approximates each tip vortex as a helical vortex tube of infinite extent while the second is based on a previously published study and uses a two-dimensional approximation to model the tip vortex interaction and represents the velocity field induced by the tip vortices as a piecewise function for which the flow incident on the downstream blade row must be calculated numerically. The unsteady loading on the downstream propeller blades is determined from the incident flow predicted using either of the models and is used to calculate the radiated sound field using an analytic propeller noise formula.
    No preview · Conference Paper · May 2009
  • Rod H. Self · Mahdi Azarpeyvand
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · May 2009 · Acoustical Physics
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jun 2008 · The Journal of the Acoustical Society of America
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a generic 3-dimensional ray-theory based model to predict installation effects on a distributed jet source for aircraft with under-wing mounted engines. The model extends previous work by improving the hot jet blockage model from a 2-dimensional empirical model to a fully 3-dimensional semiempirical model. This new model is based on static rig test experiments described in this paper. Further improvements are made including variable directivity of the jet source (rather than an omni-directional assumption) which is important in predicting the correct reflection strengths for sources downstream from the nozzle. The directivity is determined both from analytic models and empirically using recently acquired data. The completed enhanced model is then validated using data acquired from a comprehensive novel set of installation tests carried out at QinetiQ's Noise Test Facility. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
    No preview · Conference Paper · May 2008
  • Rod H. Self · Mahdi Azarpeyvand
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Apr 2008 · International Journal of Aeroacoustics

  • No preview · Conference Paper · May 2007
  • Rod Self · Mahdi Azarpeyvand
    [Show abstract] [Hide abstract]
    ABSTRACT: Modeling the frequency dependency of different defining parameters, such as time- and length-scale plays an important role in the accuracy of predictions for the noise emanating from a turbulent flow, such as jet flow. Many research workers have considered this problem, usually using a mathematical model for the form of the frequency dependence which does not necessarily stem from the physics of the turbulence, but is instead chosen to fit measurements or to give a good acoustic prediction. In this paper the underlying physics of the turbulent flow is considered in the derivation of a suitable time-scale, and this is shown to have the merit that frequency dependence arises naturally. This time-scale is shown to be related to the turbulent energy transfer rate. The time scale is then used in the prediction of noise from an isothermal subsonic coplanar jet working at two flow velocities. Essential fluid dynamic information and turbulent parameters have been obtained using a modified k- ε method, and the jet noise directivity is studied using the MGBK method. The results clearly show an improved noise prediction after using the new time-scale in comparison with some more traditional definitions.
    No preview · Conference Paper · May 2007
  • [Show abstract] [Hide abstract]
    ABSTRACT: Typically, outdoor engine measurement test sites (such as the Rolls-Royce test bed at Hucknall, UK) utilise near-ground based microphone arrays that are up to 3m below the engine exhaust exit. The rationale for choosing a near-ground microphone array over pylon-mounted arrays (typical in some anechoic installations such as the QinetiQ facility at Pyestock, UK) is that it overcomes any need to account for ground reflections. However, there are a number of possible disadvantages associated with ground-based microphones, which have not been systematically investigated before. These include refraction effects due to variations in atmospheric conditions with height, and loss of coherence due to turbulence in the surface boundary layer. If these can be properly accounted for it may be the case that the use of pylon mounted microphone arrays would yield more information than the near-ground counterpart. Equally, a model of these atmospheric effects will facilitate a better understanding of the relationship between open-air test site measurements and those made in controlled anechoic environments. This paper presents a first step towards such an investigation. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
    No preview · Conference Paper · May 2004