Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session GH: Acoustics II |
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Chair: Tim Colonius, California Institute of Technology Room: Salt Palace Convention Center 250 B |
Monday, November 19, 2007 10:30AM - 10:43AM |
GH.00001: Negative radiation forces on spheres illuminated by acoustic Bessel beams. Philip L. Marston, David B. Thiessen An analytical solution for the scattering of an acoustic Bessel beam by a sphere centered on the beam has made it possible to explore the way the acoustic radiation force on elastic and fluid spheres depends on beam and material parameters. Situations have been previously noted where, even in the absence of absorption, the radiation force of the beam on the sphere is opposite the direction of beam propagation [1]. In extensions of that work, conditions have been identified for such a force reversal on solid spheres and elastic shells. Negative radiation forces may be useful for manipulation of objects in reduced gravity and of biological cells (with single beam acoustic tweezers). The finite element method (FEM) has been used to evaluate the total acoustic field in the region near the sphere. This makes it possible to evaluate the radiation force from numerical integration of an appropriate projection of the Brillouin radiation stress tensor. FEM and analytical results agree for plane wave and Bessel beam illumination. 1. P. L. Marston, J. Acoust. Soc. Am. 120, 3518-3524 (2006). [Preview Abstract] |
Monday, November 19, 2007 10:43AM - 10:56AM |
GH.00002: ABSTRACT WITHDRAWN |
Monday, November 19, 2007 10:56AM - 11:09AM |
GH.00003: Transversal and longitudinal velocity derivative statistics in shearless turbulence Michele Iovieno, Daniela Tordella, Peter Bailey We present the temporal evolution of longitudinal and transversal velocity derivative statistics - third and fourth moments - computed by means of DNS, in decaying shearless turbulence mixings. The mixings are generated by the interaction of two isotropic turbulent flows in the absence of a mean shear. The statistics are parameterized on the kinetic energy ratio of the two fields. Inside the mixing, these statistics depart from Gaussian values seen in isotropic turbulence. The anisotropy level reduces with the magnitude of the kinetic energy ratio. Values as high as 55 for the longitudinal kurtosis and 38 for the transversal kurtosis are observed for a kinetic energy ratio of 10$^{4}$. In general, on the contrary of what is seen in the velocity statistics, it is observed that the asymptotic values of the velocity derivative statistics depend on the kinetic energy ratio. [Preview Abstract] |
Monday, November 19, 2007 11:09AM - 11:22AM |
GH.00004: Prediction of the noise of flow over a cylinder by direct computation and acoustic analogy Ali Mani, Meng Wang, Parviz Moin The sound field of flow over a circular cylinder at $Re_{D}=3900 $ and $Ma=0.4$ is evaluated using Large-Eddy Simulation (LES). The acoustic results computed directly from LES are compared with those obtained using an integral solution of the Ffowcs Williams-Hawkings (FW-H) equation in conjunction with the LES source field data. The modified FW-H solution is derived using a free-space Green function which accounts for the uniform mean flow and spanwise periodicity in the flow simulation. In the implementation of the FW-H solution, the cylinder surface and three porous surfaces with different distances from the cylinder are used as integration surfaces. The effect of turbulent flow structures crossing the integration boundary on the generation of artificial noise is studied. The quadrupole terms in the FW-H equation are found to be important in canceling artificial noise regardless of their physical significance. Alternative formulations of acoustic analogy that can better handle the boundary terms will be discussed. [Preview Abstract] |
Monday, November 19, 2007 11:22AM - 11:35AM |
GH.00005: Entropy generated noise : a comparison between compressible simulations and Golstein's acoustic analogy Alexis Giauque, Anne Laure Birbaud, Heinz Pitsch Combustion noise is one of the main noise sources of aircraft auxiliary power unit gas turbine engines, and with the better understanding of jet and fan noise, combustion generated noise is also becoming increasingly important for the the main aircraft engines. Combustion generated noise comes from two major sources: direct noise, produced by the unsteady heat release, and indirect noise, produced by entropy fluctuations passing through pressure gradients in the turbine. Two approaches are considered to investigate the fundamental aspects of indirect noise. For the first, high order fully compressible simulations of a modulated entropy wave passing through a converging diverging nozzle are performed. The second approach uses a flow solver based on Goldstein's analogy in order to propagate the acoustic and entropy waves using the perturbed velocity, pressure, and entropy components coming from low Mach number or fully compressible calculations. The capability of these two methods to predict the acoustics produced by the modulated entropy wave are finally discussed. Numerical results are compared to the experiment performed by Bake et al. (GT2005-69029, ASME Turbo Expo 2005). [Preview Abstract] |
Monday, November 19, 2007 11:35AM - 11:48AM |
GH.00006: Numerical simulation of shock wave generation and focusing in shock wave lithotripsy Jeff Krimmel, Tim Colonius Shock wave lithotripsy is a procedure where focused shock waves are fired at kidney stones in order to pulverize them. Many lithotripters with different source mechanisms and reflector shapes (or lenses) are in clinical use, but accurate prediction of focal region pressure is made difficult by nonlinearity and cavitation. We report on development of a numerical simulation framework aimed at accurate prediction of focal region flow physics. Shock wave generation and beam focusing are simulated via the Euler equations with MUSCL-type shock capturing scheme and adaptive mesh-refinement (Berger and Oliger, 1984). In future work, a bubbly cavitating flow model will be added. Electrohydraulic, electromagnetic, and piezoelectric lithotripters are modeled with axisymmetric and three-dimensional geometries. In the electrohydraulic case, a simple expanding bubble model simulates spark firing. In the piezoelectric case, a boundary condition prescribing the motion of individual elements is used. Amplitudes and durations of calculated focal region waveforms are in reasonable agreement with experimental data. [Preview Abstract] |
Monday, November 19, 2007 11:48AM - 12:01PM |
GH.00007: Linear Stability Analysis of Chevron Jet Profiles Kristjan Gudmundsson, Tim Colonius We investigate the linear stability characteristics of mean flows produced by round, and serrated (chevron) nozzles. We derive a generalized Rayleigh equation for mean-flows composed of an arbitrary number of azimuthal harmonics, allowing fast solution of the chevron stability problem via a shooting method applied to a system of ODEs.Using time-averaged turbulent mean-flows from PIV and RANS data, we compute the stability characteristics of various chevron/round nozzles. We find there are two main differences between the chevron and round jet: chevron jet growth rates are suppressed and peak growth rates shifted to lower frequencies while phase speeds are somewhat increased. We compare our instability wave results to microphone array measurements. Our results indicate that the hydrodynamic pressure field of both round, and chevron jets is consistent with that of the instability modes of the turbulent, spreading mean flow. [Preview Abstract] |
Monday, November 19, 2007 12:01PM - 12:14PM |
GH.00008: ABSTRACT WITHDRAWN |
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