Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E20: HydroacousticsAcoustics
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Chair: Vincenzo Armenio, University of Trieste Room: 704 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E20.00001: Analysis of rotor noise using LES Jacob Keller, Praveen Kumar, Krishnan Mahesh The flow field of a five-bladed marine propeller operating at design condition, obtained using large eddy simulation (LES), is used to calculate far-field sound. Three acoustic formulations are used: a point force dipole model, Curle acoustic analogy, and Ffowcs--Williams and Hawkings acoustic analogy. Each formulation is derived from the Navier--Stokes equations and the effects of the underlying assumptions are examined. The acoustic surface for the Curle and Ffowcs--Williams and Hawkings acoustic analogies is chosen to be the propeller; the propeller is split into a collection of acoustically compact radial strips. The computed sound is analyzed and the physics of sound generation is inspected. Results including far-field sound spectra and directivity will be discussed. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E20.00002: Assessment of methodologies for the solution of the Ffowcs Williams and Hawkings equation using LES of incompressible single-phase flow around bluff bodies Vincenzo Armenio, Marta Cianferra, Sandro Ianniello The Ffowcs Williams and Hawkings (FW-H) equation is used for the prediction hydrodynamic noise. We first derive the convective formulation of the volume terms of the FW-H equation. Successively, different solution strategies of the FW-H equation are evaluated using a fluid dynamic dataset obtained through large eddy simulation of a turbulent flow around a finite cylinder with square section. Specifically, the fluid dynamic noise is computed by a simple linear (Curle) approach, by the porous formulation, through direct volume integration of the nonlinear noise sources and using combination of porous and volume integration. The analysis allows to point out the strengths and drawback of the different techniques and to achieve, through the comparison of the different solutions, an accurate understanding of the noise source mechanisms taking place in the flow. Finally, we analyze the hydrodynamic noise generated by three simple, still significant, bluff bodies, namely a cube, a sphere and a prolate spheroid. The analysis shows that a streamlined body is able to produce a pressure signal one order of magnitude lower than a bluff geometry. Also, the presence of sharp corners enhances the acoustic field both in amplitude and in frequencies. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E20.00003: Temperature Control in a Franz Diffusion Cell Skin Sonoporation Setup Jeremy Robertson, Sid Becker In vitro experimental studies that investigate ultrasound enhanced transdermal drug delivery employ Franz diffusion cells. Because of absorption, the temperature of the coupling fluid often increases drastically during the ultrasound application. The current methodologies for controlling the coupling fluid temperature require either replacement of the coupling fluid during the experiment or the application of a time consuming duty cycle. This paper introduces a novel method for temperature control that allows for a wide variety of coupling fluid temperatures to be maintained. This method employs a peristaltic pump to circulate the coupling fluid through a thermoelectric cooling device. This temperature control method allowed for an investigation into the role of coupling fluid temperature on the inertial cavitation that impacts the skin aperture (inertial cavitation is thought to be the main cause of ultrasound induced skin permeability increase). Both foil pitting and passive cavitation detection experiments indicated that effective inertial cavitation activity decreases with increasing coupling fluid temperature. This finding suggests that greater skin permeability enhancement can be achieved if a lower coupling fluid temperature is maintained during skin insonation. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E20.00004: Noise Production of an Idealized Two-Dimensional Fish School Nathan Wagenhoffer, Keith Moored, Justin Jaworski The analysis of quiet bio-inspired propulsive concepts requires a rapid, unified computational framework that integrates the coupled fluid-solid dynamics of swimmers and their wakes with the resulting noise generation. Such a framework is presented for two-dimensional flows, where the fluid motion is modeled by an unsteady boundary element method with a vortex-particle wake. The unsteady surface forces from the potential flow solver are then passed to an acoustic boundary element solver to predict the radiated sound in low-Mach-number flows. The coupled flow-acoustic solver is validated against canonical vortex-sound problems. A diamond arrangement of four airfoils are subjected to traveling wave kinematics representing a known idealized pattern for a school of fish, and the airfoil motion and inflow values are derived from the range of Strouhal values common to many natural swimmers. The coupled flow-acoustic solver estimates and analyzes the hydrodynamic performance and noise production of the idealized school of swimmers. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E20.00005: Strong wave/mean-flow coupling in baroclinic acoustic streaming Greg Chini, Guillaume Michel Recently, Chini \emph{et al.} [\emph{J. Fluid Mech.}, Vol. 744 (2014)] demonstrated the potential for large-amplitude acoustic streaming in compressible channel flows subjected to strong background cross-channel density variations. In contrast with classic Rayleigh streaming, standing acoustic waves of $\mathit{O}(\epsilon)$ amplitude acquire vorticity owing to baroclinic torques acting throughout the domain rather than via viscous torques acting in Stokes boundary layers. More significantly, these baroclinically-driven streaming flows have a magnitude that also is $\mathit{O}(\epsilon)$, i.e. comparable to that of the sound waves. In the present study, the consequent potential for fully two-way coupling between the waves and streaming flows is investigated using a novel WKBJ analysis. The analysis confirms that the wave-driven streaming flows are sufficiently strong to modify the background density gradient, thereby modifying the leading-order acoustic wave structure. Simulations of the wave/mean-flow system enabled by the WKBJ analysis are performed to illustrate the nature of the two-way coupling, which contrasts sharply with classic Rayleigh streaming, for which the waves can first be determined and the streaming flows subsequently computed. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E20.00006: The Water music of Vanuatu Tadd Truscott, Randy Hurd, Jesse Belden, Nathan Speirs, Andrew Merritt, John Allen Female musicians from the northern islands of Vanuatu (within larger Polynesia) use the water surface as an instrument to create a variety of unique sounds. Water music is often made by a line of performers standing side by side, waist deep in clear island waters. Accompanied by singing, the women work in unison exhibiting several percussive techniques, which include striking the water surface and throwing handfuls of water which scatter into droplets before impacting the surface. Each interaction produces a unique acoustic response corresponding to the air-water-hand interaction. We highlight the connection between water interaction, cavity shape and the resulting sound which was discovered by these people through their own experimentation. [Preview Abstract] |
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