Acoustic Far Field - Explore the Science & Experts | ideXlab

Scan Science and Technology

Contact Leading Edge Experts & Companies

Acoustic Far Field

The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform

Anastasios S Lyrintzis – 1st expert on this subject based on the ideXlab platform

  • surface integral methods in computational aeroAcoustics from the cfd near Field to the Acoustic Far Field
    International Journal of Aeroacoustics, 2003
    Co-Authors: Anastasios S Lyrintzis

    Abstract:

    A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-Field CFD results to the Acoustic FarField is given. These integral formulations (i.e. Kirchhoff’s method, permeable (porous) surface FfowcsWilliams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the FarField sound, instead of the volume integrals required by the traditional Acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-Field solution in the near Field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the FarField are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-Field CFD data. Both methods can be extended in orde…

  • Surface integral methods in computational aeroAcoustics—From the (CFD) near-Field to the (Acoustic) FarField
    International Journal of Aeroacoustics, 2003
    Co-Authors: Anastasios S Lyrintzis

    Abstract:

    A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-Field CFD results to the Acoustic FarField is given. These integral formulations (i.e. Kirchhoff’s method, permeable (porous) surface FfowcsWilliams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the FarField sound, instead of the volume integrals required by the traditional Acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-Field solution in the near Field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the FarField are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-Field CFD data. Both methods can be extended in orde…

  • Rotorcraft impulsive noise prediction using a rotating Kirchhoff formulation
    Journal of Aircraft, 1996
    Co-Authors: Anastasios S Lyrintzis, Evangelos K. Koutsavdis

    Abstract:

    Rotorcraft impulsive [i.e., high-speed impulsive (HSI) and blade-vortex interaction (BVI)] noise for an advancing rotor is studied numerically. The unsteady transonic full-potential rotor code is used for the simulation of the near-Field flow. A rotating Kirchhoff’s method is used for the extension to the Acoustic Far Field. The formulation is extended for an advancing rotor and an observer fixed relative to the rotor, and thus, moving relative to the freestream, and allows a direct comparison with experiments. Results for both HSI and BVI noise are presented and compared with experimental results. Various noise parameters are identified and investigated. The rotating Kirchhoff noise appears to be a very valuable tool for helicopter impulsive noise prediction.

Theodore B. Norris – 2nd expert on this subject based on the ideXlab platform

  • Nanoscale coherent Acoustic phonon imaging
    Ultrafast Phenomena in Semiconductors and Nanostructure Materials X, 2006
    Co-Authors: B. C. Daly, Theodore B. Norris, Julien Klein, Donald Milan Tennant, Joseph Ashley Taylor, J.e. Bower

    Abstract:

    An ultrafast optical pump and probe technique known as picosecond ultrasonics is used to generate and detect coherent Acoustic phonon pulses in nanostructured films grown on Si wafers. By detecting the phonons after they have diffracted across a millimeter thick wafer, it is possible to measure the scattered phonons in the Acoustic Far Field. Numerical backpropagation algorithms can then be used in order to reconstruct the object which scattered the Acoustic phonon pulses. We describe measurements and simulations of experiments performed on surface and sub-surface nanostructures. Results with ~500 nm image resolution are shown, and plans for improving that resolution by an order of magnitude will be described.

  • Gouy phase shift of single-cycle picosecond Acoustic pulses
    Applied Physics Letters, 2003
    Co-Authors: N. C. R. Holme, B. C. Daly, M.t. Myaing, Theodore B. Norris

    Abstract:

    Ultrafast laser pulses are used to generate single-cycle picosecond Acoustic pulses in thin metal films on silicon. For small initial excitation spot sizes, propagation of the Acoustic pulses across a 485-μm Si crystal leads to significant diffraction effects. The temporal reshaping of the Acoustic wave form due to diffraction is investigated, and we demonstrate that the Acoustic Far Field can be reached.

  • Gouy phase shift of single-cycle picosecond Acoustic pulses
    The Thirteenth International Conference on Ultrafast Phenomena, 2002
    Co-Authors: N. C. R. Holme, B. C. Daly, M.t. Myaing, Theodore B. Norris

    Abstract:

    Ultrafast laser pulses are used to generate single-cycle picosecond Acoustic pulses in thin metal films on silicon. For small initial excitation spot sizes, propagation of the Acoustic pulses across a 485-mm Si crystal leads to significant diffraction effects. The temporal reshaping of the Acoustic wave form due to diffraction is investigated, and we demonstrate that the Acoustic Far Field can be reached. © 2003 American Institute of Physics. @DOI: 10.1063/1.1590405#

Leonhard Kleiser – 3rd expert on this subject based on the ideXlab platform

  • Linear stability and Acoustic characteristics of compressible, viscous, subsonic coaxial jet flow
    Physics of Fluids, 2013
    Co-Authors: Michael Gloor, Dominik Obrist, Leonhard Kleiser

    Abstract:

    This study explores the parameter influence on the linear stability characteristics of viscous compressible coaxial jet flow at subsonic flow velocities. We study the impact of parameters on the disturbance development, such as the Reynolds number, Mach number, momentum thickness, temperature and velocity ratio between bypass flow and core stream as well as the influence of the azimuthal wavenumber. In addition to the discussion on the unstable modes, we also investigate the properties of Acoustic (radiating) modes which are relevant for sound propagation to the Acoustic FarField. By analyzing the eigenfunction profiles of the Acoustic modes, we identify a possible interaction mechanism between the shear layer and the Acoustic modes.

  • Localization of Acoustic sources in subsonic jets
    Pamm, 2008
    Co-Authors: Dominik Obrist, Leonhard Kleiser

    Abstract:

    The sound in the Acoustic FarField of a round jet is generated by a multitude of unsteady flow structures with different len gth and time scales. Most likely, different components of the noise spectrum are created by different structures in the jet w hich emit sound in different directions. Based on Lighthill’s ac oustic analogy, we present a method for relating flow structu res of the jet with FarField noise spectra and their associated dir ectivity patterns. The method allows to determine what kind of noise (with respect to frequency and emission direction) is generated at a given streamwise location. We illustrate the method with numerical results for a round isothermal jet. Copyright line will be provided by the publisher

  • an euler solver for the Acoustic Far Field prediction of compressible jet flow
    Pamm, 2007
    Co-Authors: Felix Keiderling, Dominik Obrist, S B Muller, Leonhard Kleiser

    Abstract:

    We report on a highly accurate Euler solver for predicting FarField jet noise. The solver is based on a framework for Direct Numerical Simulation (DNS) / Large-Eddy Simulation (LES) that provides the time-dependent, noise-generating flow Field and the Acoustic near-Field. The corresponding FarField is then computed by solving the inviscid Euler equations in a conservative formulation which is discretized with compact finite differences. Numerical stability can be guaranteed by a spectrally selective filtering procedure developed in the context of subgrid-scale modeling which is active only in the high wavenumber regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)