Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D20: Acoustics II: General |
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Chair: Christophe Millet, CEA Room: 2008 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D20.00001: Schlieren imaging of shock waves radiated by a trumpet Pablo L. Rendon, Roberto Velasco-Segura, Carlos Echeverria, David Porta, Teo Vazquez, Antonio Perez-Lopez, Catalina Stern The flaring bell section of modern trumpets is known to be critical in determining a wide variety of properties associated with the sound radiated by these instruments. We are particularly interested in the shape of the radiated wavefront, which clearly depends on the bell profile. A horn loudspeaker is used to drive high-intensity sound at different frequencies through a B-flat concert trumpet. The sound intensity is high enough to produce shock waves inside the instrument resonator, and the radiated shocks are then visualised using Schlieren imaging. Through these images we are able to study the geometry of the shock waves radiated by the instrument bell, and also to calculate their propagation speed. The results show that propagation outside the bell is very nearly spherical, and that, as expected, the frequency of the driving signal affects the point at which the shock waves separate from the instrument. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D20.00002: Quantum Analogies in the Interaction between Acoustic Waves and Bubble Clouds Miguel A. Parrales, Javier Rodriguez-Rodriguez Analogies between quantum mechanical and acoustical propagation phenomena have a great interest in academic research due to their ability to shed light on some complex quantum effects, which are impossible to visualize directly in the macroscopic world. In this talk, we describe a number of these analogies concerning the acoustic behavior of bubble clouds. Firstly, we show that the structure of the collective oscillation modes of a spherical bubble cloud resembles that of the atomic orbitals of a hydrogen atom. Secondly, we present an analogy between some perturbation methods used in quantum-electrodynamics and the computation of the acoustic response of the randomly distributed bubble cloud by considering the contribution to the total scattered pressure of the multiple scattering paths that take place inside the clouds. As an application of this analogy, we obtain the scattering cross-section of a diluted cloud, which remarkably mimics the quantum scattering of an neutron wave when passing through an atomic nucleus. Finally, we numerically reproduce the behavior of an electron in a covalent bond between two hydrogen atoms by simulating the acoustic wave propagation through two neighboring spherical bubble assemblages. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D20.00003: A low-order model for wave propagation in random waveguides Christophe Millet, Michael Bertin, Daniel Bouche In numerical modeling of infrasound propagation in the atmosphere, the wind and temperature profiles are usually obtained as a result of matching atmospheric models to empirical data and thus inevitably involve some random errors. In the present approach, the sound speed profiles are considered as random functions and the wave equation is solved using a reduced-order model, starting from the classical normal mode technique. We focus on the asymptotic behavior of the transmitted waves in the weakly heterogeneous regime (the coupling between the wave and the medium is weak), with a fixed number of propagating modes that can be obtained by rearranging the eigenvalues by decreasing Sobol indices. The most important feature of the stochastic approach lies in the fact that the model order can be computed to satisfy a given statistical accuracy whatever the frequency. The statistics of a transmitted broadband pulse are computed by decomposing the original pulse into a sum of modal pulses that can be described by a front pulse stabilization theory. The method is illustrated on two large-scale infrasound calibration experiments, that were conducted at the Sayarim Military Range, Israel, in 2009 and 2011. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D20.00004: On Pressure Wave Simulations in Liquid Metal Neutron Source Targets Jana R. Fetzer, Andreas Class Sound waves generated by fluid flow at low Mach numbers is associated with separated scales and thus with difficulties to construct efficient numerical methods for their approximation. One method is the Multi Pressure Variables (MPV) approach introduced for aero-acoustic applications [1,2]. The MPV approach is based on a single time scale multiple space scale asymptotic analysis derived for subsonic flow by an asymptotic series expansion in the Mach-number. Distinguished are the flow and acoustic length scales resulting in three pressure contribution, i.e. thermodynamic, acoustic and dynamic pressure which are discretized on numerical meshes of different resolution. We propose to apply MPV to analyse liquid metal cooled spallation targets with a pulsed proton beams. These targets are operating in high power neutron sources for fundamental research. The nearly instantaneous heating of the liquid metal results in volumetric expansion of inertia confined liquid and thus to high pressure waves, which represent a major lifetime limiting thread. Our development accompanies design activities for the META:LIC (MEgawatt TArget: Lead bIsmuth Cooled) target proposed for the European Spallation Source. \\[4pt] [1] Munz C.-D. et al. J Computers {\&} Fluids 2003; 32\\[0pt] [2] Klein R. J. Comput Phys 1995; 121 [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D20.00005: Numerical analysis of sound propagation for acoustic lens array in different fluid mediums Kei Fujisawa, Akira Asada In this paper, an acoustic sound focusing method using acoustic lens array is investigated numerically. To understand the sound propagation in the acoustic field in water with a lens material of glycerin, compressible Navier-Stokes equation, the mass conservation, energy equation, state equation in cylindrical coordinate system are solved without applying parabolic approximation. The numerical method is based on the finite difference time domain method. The numerical calculation of the sound propagation is carried out in the near field of the acoustic lens array of variable thickness normal to the acoustic beam. The numerical result shows that the sound pressure level along the beam axis increases due to the influence of the acoustic lens array, which indicates the capability of the acoustic lens array to the sound focusing. [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D20.00006: Global mode and frequency response analysis of low-density jets W. Coenen, L. Lesshafft, X. Garnaud, A. Sevilla We present a global stability analysis of a low-density jet, where the wavepacket structures are temporal eigenmodes of the linearized equations of motion in a 2D domain. As a base state we employ a numerical solution of the low-Mach number Navier-Stokes equations. The jet is characterized through the jet-to-ambient density ratio, the Reynolds number, and the momentum thickness of the velocity profile at the jet exit plane. The linear global mode analysis shows that for certain combinations of the control parameters, an isolated eigenmode dominates the eigenvalue spectrum. Its associated growth rate can be used to construct a neutral curve in the parameter space that agrees well with the experimentally observed onset of self-sustained oscillations (Hallberg \& Strykowski, JFM, 2006). However, for high values of the Reynolds number, the construction of a neutral curve based on the spectrum loses validity, since for these cases the spectrum is dominated by a continuous branch of eigenvalues, sensitive to changes in domain length and grid refinement. Finally, the flow response to external forcing in a globally stable setting is investigated through the computation of the pseudospectrum, and is found to be dominated by a resonance of the stable eigenmode. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D20.00007: ABSTRACT WITHDRAWN |
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