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2001 ACOUSTICS AREA SEMINARS ARCHIVE
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SPRING SEMINARS |
FALL SEMINARS
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2001 SPRING SEMINAR SCHEDULE
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Jan 26
Antonios Apostolou,
Graduate Program in Acoustics,
Pennsylvania State University, and
Schlumberger Oilfield Services
The Underwater Sounds from the Impact of Drops in Superfluid 4He
When a drop of a liquid impacts onto a liquid surface, a crater is formed and the cavity dynamics that follow determine
whether or not a bubble will be entrained. The entrainment of an air bubble following the impact of a raindrop onto
the sea provides the predominant mechanism for the production of the underwater noise from rain. Experiments in
water have indicated one particular entrainment region in a dimensionless parameter-space. This talk describes an
ongoing research effort to study the phenomenon on a more fundamental basis using, instead of water, the pure and
highly characterized liquid helium. The impact of liquid helium drops onto a liquid helium surface is monitored by
employing acoustic and optical techniques. Bubble entrainment in superfluid 4He, as well as the transition to
non-entrainment, are observed, and the collected data indicate a new entrainment region. In addition, high-speed
images of the crater motion reveal novel crater dynamics for the non-entrainment case.
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Feb 2
Dr. Nicholas P. Chotiros,
Applied Research Laboratories,
The University of Texas at Austin
Inversion of Biot Parameters for Water Saturated Sand
An inversion of the Biot model using measured acoustic properties suggests a modification of the Biot-Stoll equations
as they apply to the propagation of sound in water saturated sand. The Biot model of sound propagation in porous
media, as formulated by Stoll, requires 13 input parameters to generate acoustic properties. The input parameters may
be divided into three groups according to the accuracy with which they are known. The first group contains tabulated
physical constants, the second group is less precisely known, and the third group is simply not measurable. An
inversion procedure was devised to estimate the immeasurable group from simple acoustic measurements---reflection
loss, compressional and shear wave speeds, and attenuations. Although the inversion process is nonlinear, in practice it
is well behaved and converges quite rapidly to a unique solution. The issue of imprecisely known parameter values was
handled in a probabilistic manner. The inversion results for water saturated sand, based on published laboratory and
in-situ measurements, show a definite incompatibility between the physical and acoustical measurements. In an attempt
to find a solution, two possible hypotheses are put forward: (1) the inclusion of some proportion of the pore fluid
within the frame, and (2) the coefficient of fluid content as an independent variable. The latter proved to be the only
plausible solution, requiring one change in the Stoll formulae and an additional independent parameter. It implies that
the solid frame cannot be considered to be uniformly elastic.
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Feb 9
Dr. Kenneth Huang and Andrew Morrison,
Motorola Network Systems, Ft. Worth, Texas
An Application of Acoustic Design in Telecommunications
Initially telecommunications equipment was concealed in maintenance areas or rooftops. The miniaturization of
electronics and the growth of the cellular market has permitted base station equipment to be located nearer to
human observers (e.g., utility poles, sides of residences, and business offices). This in turn has created increased
concern about acoustic noise generated by the cellular telecommunications base station equipment, which is one
subject that will be addressed in this seminar. We shall also provide an overview of electronic packaging trends,
the future of cellular telephony, the cellular base station environment, and examples of Motorola products.
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Feb 16
Dr. Timothy Walsh,
Institute for Computational Engineering and Sciences,
The University of Texas at Austin
Boundary Element Modeling of the External Human Auditory System
Within the context of the external auditory system, a benchmark that is used by acousticians and audiologists is the
head-related transfer function (HRTF). The HRTF is used in understanding the localization process, deducing
resonance modes of the ear canal, as well as in the design of hearing aids and virtual acoustic simulators. It is
normally measured experimentally in an anechoic chamber using a rotating frame. Although numerical simulations
provide an alternative approach for generating the HRTF, their application presents several challenges to the
numerical analyst, including accurate representation of the geometry, mesh adaptivity for boundary element
methods, and parallelization. These issues will be addressed briefly in this talk. Following the discussion of the
numerical algorithms, the results of the numerical computation of the HRTF will be presented and compared with
experimental data from the literature. The quarter-wave resonance modes and the corresponding surface pressure
distributions of the concha and ear canal will be deduced from the numerical HRTF and compared with experimental
observations from the literature. The numerical results show the negligible effect that the ear canal has on spatial
cues, and thus on the localization process as well. Computations on meshes with and without the ear canal will give
some insight into the acoustical effect of terminating the canal with a hearing aid, or some other acoustical device.
Initially telecommunications equipment was concealed in maintenance areas or rooftops. The miniaturization of
electronics and the growth of the cellular market has permitted base station equipment to be located nearer to
human observers (e.g., utility poles, sides of residences, and business offices). This in turn has created increased
concern about acoustic noise generated by the cellular telecommunications base station equipment, which is one
subject that will be addressed in this seminar. We shall also provide an overview of electronic packaging trends,
the future of cellular telephony, the cellular base station environment, and examples of Motorola products.
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Feb 23
Lee Thompson,
Applied Research Laboratories,
The University of Texas at Austin
Three-Dimensional Ultrasound Imaging with Blazed Acoustic Arrays and Time-Frequency Beamforming
A novel solution to reducing hardware requirements for 3D acoustic imaging is described. The solution is based on
high-resolution imaging sonar miniaturization research currently underway at ARL:UT. The research combines
techniques used in radar, optics, and time-frequency signal processing to significantly reduce the cost, size, and
power of acoustic imaging systems. Frequency-scanning radar involves the use of frequency to steer the radar
beam. This technique typically employs delay lines in antenna array transmitters that introduce phase shifts which
permit frequency to determine the steering angle of the main beam, and it is referred to as angular frequency
dispersion. In optics, angular frequency dispersion is accomplished with prisms and gratings. If one combines
techniques similar to the frequency-scanning techniques of radar with blazed acoustic array (grating) design
techniques from optics and time-frequency signal analysis techniques, a single-channel acoustic imaging system can
be created. This imaging system requires only a single hardware channel (one stave) from the array to generate a
2D image, because the blazed array effectively multiplexes the beam signals into separate frequency channels.
Consequently, the beamformer for such a blazed receiver signal can be designed around a time-frequency distribution,
such as a short-time Fourier transform. If this technique is used orthogonal to conventional array design and
beamforming techniques, a 3D acoustic imaging system can be designed around the same number of hardware
channels required for a conventional 2D system.
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Mar 2
David Nelson,
Nelson Acoustical Engineering, Inc., Elgin, Texas
Adventures in Acoustical Consulting: 1985-2001
This seminar will chronicle the journey of one UT acoustics graduate from the well-ordered heights of academia into
the maelstrom of real-world acoustics and noise control. The discussion will include numerous short case histories,
anecdotal examples and observations from 15+ years of professional experience, with an emphasis on the "black art"
of noise control at the source. Recent projects of interest include low-noise design for experimental packages flying
on the International Space Station, noise and vibration control for mixed-use buildings with large shock and vibration
sources, a multi-channel acoustical data acquisition system, and noise control for a 125-acre industrial plant. Along the
way we'll encounter such noise control challenges as squeaking valves, howling pipes, shrieking saw blades, and noisy
fans, all of which were solved at the source without recourse to conventional "noise control materials." The talk will
reveal the complex, multi-disciplinary, and practical aspects of this work and will provide an overview of what it's
really like to successfully practice noise control engineering.
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Mar 23
Dr. Alexander Voishvillo,
Cerwin-Vega, Inc., Simi Valley, California
Application of Multitone Stimulus to Modeling and Analysis of Air-Related Nonlinear Distortion in Sound Systems
Multitone stimulus is used in identification of weakly nonlinear systems and for assessment of nonlinearity in sound
and broadcasting equipment. Spectral and statistical characteristics of multitone signals resemble those of musical
signals, and the response to multitone stimulus yields more useful information about nonlinearity than conventional
measurements of harmonic and two-tone intermodulation distortion. Previous work has demonstrated that strong
harmonic and intermodulation distortion accompanies the propagation of waves radiated by large horn arrays. Our
group has recently developed propagation models for 1D multitone waves in horns. The modeling is based on
numerical solution of implicit equations describing distorted waveforms. It takes into account linear propagation of
the fundamental tones and their reflections from the mouth, and the nonlinear, reflection-free propagation of
distortion products. Further research may include radiation of multitone waves by a complex source, substitution of
multitone stimulus by a musical signal to provide listening tests, and auralization of propagation nonlinearity in horns
and in freely propagating waves radiated by complex sources such as large horn arrays. The propagation model
already provides auralization of nonlinear distortion in 1D waves of finite amplitude. Data obtained from modeling
may be used to build Volterra models of nonlinear propagation. Such models may lead to signal processing solutions
to minimize distortion in propagating waves.
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Mar 30
Dr. Brian Storey,
Franklin W. Olin Cockrell School of Engineering, Needham, Massachusetts
Gas Dynamics, Mass Transfer, and Chemical Reactions in Violently Collapsing Bubbles
In sonochemistry, sonoluminescence, and shock-wave lithotripsy, micron-size bubbles are subjected to intense
ultrasound fields. Often, bubbles in these applications experience a long, slow expansion before undergoing a
collapse so violent that the contents of the bubble can become sufficiently hot to emit a brief flash of light. Because
of the extreme nonlinearity of the bubble oscillations, excess water vapor is trapped in the bubble during this
violent collapse. The water is prevented from exiting the bubble by the relatively slow rate of mass diffusion and
non-equilibrium condensation. Consideration of the trapped vapor is crucial to understanding the physical processes
occurring during the collapse. Through the use of computational fluid dynamics, the flow, transport and chemistry
occurring in the interior of the bubble were modeled in great detail. With these computational models as a basis, the
important physical processes can be understood and more practical, reduced models can be developed. The models
provide reasonable predictions of experimental sonochemistry yields, the stability threshold of sonoluminescence
experiments, and the rather extreme behavior of bubbles in shock-wave lithotripsy.
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Apr 4
Dr. Lawrence A. Crum, Center for Industrial and Medical Ultrasound,
Applied Physics Laboratory,
University of Washington
Single Bubble Sonoluminescence
When an acoustic wave of moderate pressure amplitude is propagated through an aqueous liquid, light emissions can be
observed. This conversion of mechanical energy into electromagnetic energy is called Sonoluminescence (SL) and
represents an energy amplification per molecule of over eleven orders of magnitude! Recently, we made the discovery
that a single, stable gas bubble, acoustically levitated in a liquid, can emit optical emissions each cycle for an unlimited
period of time. Presumably, the oscillations of the bubble cause the gas in the interior to be heated to incandescent
temperatures during the compression portion of the cycle. Furthermore, some recent experimental evidence indicates
that the lifetime of the optical pulse is less than 50 picoseconds, and that the temperature in the interior of the bubble can
exceed 100,000 K. Most conventional explanations for the phenomenon are unsatisfying and it is likely that some
rather unusual physics is occurring. The best explanation, at the moment, is that a shock wave is created in the gas which
is then elevated to high temperatures by inertial confinement. If shock waves are the mechanism for SL emission, then
optimization of the process could lead to extraordinary physics, including nuclear fusion. This phenomenon has captured
the imagination of a wide variety of individuals, from serious scientists to movie producers---the movie Chain Reaction
was (loosely) based upon SL. A brief review of this intriguing phenomenon will be presented as well as my frustrating
attempts to explain its potential (and its limitations) to the news media and the general public.
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Apr 5
Dr. Lawrence A. Crum, Center for Industrial and Medical Ultrasound,
Applied Physics Laboratory,
University of Washington
Medical Application of Acoustics
Medical ultrasound technology is experiencing a rebirth as methods and applications extend beyond current diagnostic
imaging to include novel therapeutic and surgical uses. These applications broadly include: Tissue ablation, cautery,
lipoplasty, and hemostasis via targeted non-invasive thermal deposition; site-specific and ultrasound mediated drug
activity; novel imaging approaches using ultrasound contrast agents and signal processing; extra-corporeal lithotripsy;
and enhancement of natural physiological functions such as wound healing and tissue regeneration. This general lecture
will address some of the basic scientific questions and future challenges in the areas listed above. We shall particularly
emphasize the use of High Intensity Focused Ultrasound (HIFU) in the treatment of hemorrhagic trauma and related
pathological conditions, especially in organs which are difficult to treat using conventional medical and surgical
techniques. Direct applications include combat casualty care, as well as many civilian uses in non-invasive or minimally
invasive trauma management, bloodless surgery, and ultrasound-mediated drug therapy. We shall also explore
imaging and simulation techniques associated with treatment, targeting, and monitoring the effects of HIFU therapy.
Finally, we shall describe our efforts to successfully transition the scientific developments in our laboratory to
commercial products, and thus will describe our attempts to start new companies or work with existing ones to
implement technology transfer.
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Apr 20
Mark Genfan,
Acoustic Spaces, Martindale, Texas
Acoustical Design of Studios and Theaters
Acoustic Spaces is involved mainly in the design and installation of recording studios, video facilities and other
high-end technical facilities. We also design and provide consultation services for public theaters, home theaters, and
various commercial clients. This seminar will describe the backgrounds and training of personnel within the company.
The design process will be discussed, particularly the interaction with clients to ensure that acoustical and practical,
ergonomic considerations are properly combined. Emphasis will be given to software and other tools used in the
design process, as well as acoustical properties, materials and devices. Current trends will be described, as well as
recent technological advances used in studios and theaters, both public and home, and how they impact acoustical
design considerations. Examples of AutoCAD drawings and acoustical analysis of rooms and spaces will be shown.
Coordination with architects and builders will be addressed, as well as budgets and other business aspects of
acoustical consulting.
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May 1
Jack W. Reed,
JWR, Inc., Albuquerque, New Mexico
Airblast from TWA Flight 800
Nearly 300 FBI witness interviews reported a bang or bangs associated with this accident off Long Island in 1996. Most
attention, however, was devoted to visual sightings of a described variety of streaks and flashes, which were first
interpreted as rocket motor trails. This led to investigations which concentrated on recovery and study of aircraft
debris and geometric resolution of sighting descriptions. No clear evidence of any missile attack was ever found, so
efforts turned toward some other on-board source for this disaster. Various experiments concluded that a spark in the
"empty" central fuel tank could have caused the initiating explosion, and that a spark could have been generated from
the fuel meter wiring. This became the final conclusion of the National Transportation Safety Board (NTSB) Final Report,
issued in August 2000, although couched in many caveats of uncertainty. There has been controversy over NTSB
treatment of witness visual reports, but very little discussion of the reported noises. Early estimates showed that one ton
of TNT was probably needed for an explosion to shake houses and cause some of the reported bangs. However, for the
NTSB Report, NASA-Langley was tasked to look into this and concluded that the noise could have been caused by just
20 lb of TNT (a reasonable equivalent for fuel tank fume detonation). Analyses presented at this seminar should lead to
rejection of this conclusion.
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2001 FALL SEMINAR SCHEDULE
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Sep 21
Dominik Hammer,
Department of Physics,
The University of Texas at Austin
On Light Emission of Sonoluminescing Bubbles
Sonoluminescence is the emission of light from tiny gas bubbles in water that expand and contract under the influence
of an external pressure wave. Results from experiments investigating this phenomenon are shown along with our
attempts at understanding it in terms of well-known physics. Our focus is on the light emitting mechanisms which
are treated in the framework of a hydrodynamic-chemical description of the oscillating bubble: The time varying
water vapor content of the bubble is taken into account as well as chemical reactions of the water (i.e., dissociation)
and ionization of the bubble gas due to quasi-adiabatic heating of the bubble. The light emission is shown to be
mostly due to electron-neutral atom and electron-ion bremsstrahlung as well as recombination radiation. In relatively
cool bubbles, radiative attachment to oxygen and hydrogen atoms also contributes to the emission. Preliminary
results on the emission of OH signatures of very dim bubbles are presented.
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Sep 28
Dr. Tracianne B. Neilsen,
Applied Research Laboratories,
The University of Texas at Austin
Inversion for Source and Environmental Parameters in the Shallow Ocean Using a Rotated Coordinates Technique
The problem of localizing and tracking a source in the shallow ocean is often complicated by uncertainty in the
environmental parameters. A method is presented that uses a rotated coordinates technique [M. D. Collins and L.
Fishman, J. Acoust. Soc. Am. {98}, 1637-1644 (1995)] in simulated annealing to invert for both the source and the
environmental parameters. The rotated coordinates technique not only aids in the inversion process, but it also
indicates the coupling of the source and environmental parameters and the relative sensitivities of the cost function
to changes in the various parameters. The information obtained from the rotated coordinates provides insights into
how the inversion problem can be effectively decoupled. The cost function minimized in the inversion algorithm is
model-data cross-phone spectra summed coherently over phone pairs, frequency, and time sequence. The results of
applying this inversion method to simulated array data to obtain source and environmental parameters are
presented. In addition, inversion results for environmental parameters when Gaussian white noise is added to the
simulated data are given. [Work supported by ONR.]
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Oct 5
Richard E. Boner,
Boner Associates, LLC
Acoustical Design Considerations in an Unusual High School Auditorium
Over the past generation, the design of high school auditoria has evolved from simple, acoustically mediocre
shoe-box style, to a variety of designs. Among these are narrow fan-shapes, wide fan-shapes, and experimental
designs. This talk focuses on yet another design, where the school is treated to a more European type house,
complete with multiple balconies and adjustable acoustics. Acoustical design considerations are discussed, including
architectural, noise control, and electro-acoustic.
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Oct 12
Jeff DeMoss and John Parker,
Dell Computer Corp.
Acoustical Requirements for Personal Computers
A company marketing personal computers may find it necessary to provide customers with relevant acoustical
characteristics of the product. Traditional noise emission metrics, sound power and sound pressure, have normally
been used. More customers are beginning to make purchasing decisions based on the sound quality of information
technology products rather than the traditional metrics. A more relevant means of measuring customer preference
is needed to aid product designers. Innovations in technology (lower cost, processing speed, ease of use) have
made sound quality tools more available and should be explored as a means of assessing customer preference for
information technology products.
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Oct 19
Dr. Mike Bailey,
Center for Industrial and Medical Ultrasound (CIMU),
Applied Physics Laboratory,
University of Washington
Cavitation in Lithotripsy and High Intensity Focused Ultrasound Therapy
Shock Wave Lithotripsy (SWL), which uses focused shock waves to break up kidney stones, is a common and
successful clinical procedure. However, tissue injury also results in most if not all treatments. Cavitation (bubble
action) likely plays a role in both breakup and tissue damage. High intensity focused ultrasound (HIFU) is used to
thermally necrose tumors or cauterize bleeds. Treatment area control and image guidance are two challenges that
have slowed clinical acceptance. Bubbles likely play a role in distorting the lesion shape but may be very helpful in
ultrasound guidance. At CIMU we are interested in better understanding cavitation's role in lithotripsy and HIFU
and controlling it to improve both procedures. Some of our efforts are discussed in this seminar. First, the in vivo
results of work begun at UT and ARL are reported. Manipulation of the phasing but not the amplitude of a
lithotripsy pulse reduced tissue injury and cavitation. Second, overpressure (elevated static pressure) reduced tissue
injury, probably by suppressing cavitation. Our hypothesis is that at atmospheric pressure, bubbles created by one
lithotripter pulse act as cavitation nuclei for subsequent pulses and that overpressure accelerates the dissolution of
the bubbles. Numerical calculations and experimental results support the hypothesis. Third, in HIFU, lesion shape
distortion, believed caused by scattering from bubbles created thermally or acoustically, is reduced by overpressure.
However, bubbles can be used to image and to monitor the treated area. Last, some results of cavitation detection
in vivo during lithotripsy and of the application of HIFU in vivo are reported.
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Oct 26
Dr. Karl B. Fisher and Dr. Rich Gramann,
Applied Research Laboratories,
The University of Texas at Austin
Acoustics and Signal Processing Research at Applied Research Laboratories
Applied Research Laboratories (ARL), University of Texas at Austin , has been a leader in acoustic research since its
founding as the Defense Research Laboratory immediately after World War II. ARL research in acoustics has
traditionally focused on Department of Defense applications with an emphasis on Navy active and passive sonar
systems. Naval sonar systems are used in a variety of applications that include surveillance, anti-submarine warfare,
and mine and swimmer detection. The design and optimization of these sonar systems requires a thorough
understanding of the complex acoustic propagation in the ocean coupled with sophisticated signal and information
processing algorithms. Over the years, ARL's acoustic research programs have extended beyond naval applications
and presently include such efforts as automated land vehicle detection/classification systems based on combined
acoustic and seismic signatures, autonomous acoustic systems for drug interdiction, and industrial applications. ARL
is the largest organized research unit at UT Austin and consists of five research laboratories. An overview of current
ARL research in acoustics is presented in this seminar.
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Nov 2
Dr. David Grant,
Applied Research Laboratories,
The University of Texas at Austin
Mechanically Imploded Light Bulbs as Acoustic Sources
Light bulbs make handy acoustic impulse sources for underwater research. They are inexpensive, readily available
anywhere, and simple to use, requiring no special training or heavy deployment equipment. Their acoustical
properties are easily characterized in terms of their mechanical characteristics. Their acoustical levels and their
waveforms are not a threat to marine life. Because of these characteristics, light bulb sources are being used more
and more in underwater acoustics research. Knowledge of their acoustical properties is important for acoustics test
planning and test data analysis. In this work we have set out to measure the acoustical properties of only a few
types of bulbs. What makes this work unique is that we have taken many samples of each type of bulb so as to
characterize the variability. The measurements have been done under carefully controlled conditions so that the
acoustical levels are known to a high degree of accuracy. We also measured relevant physical characteristics of the
bulbs to allow comparison with theoretical treatments. To date, only a cursory comparison of the data with theory
has been done. Future work will involve a more thorough comparison with theory to see how well the acoustical
properties can be predicted from physical properties.
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Nov 16
Dr. Nicholas P. Chotiros,
Applied Research Laboratories,
The University of Texas at Austin
Nonlinear Acoustics in Water-Saturated Sand
A variety of basic acoustical experiments were performed to test the linearity of sound waves in dry and
water-saturated sand. The finite-amplitude and phase comparison methods were used to observe nonlinearity
characteristics in sand and glass bead samples. It was found that uniform glass bead samples were less linear than
sand. The fact that variations in sound speed could be induced by changing the external frame stress suggests that
the acoustic energy may be carried by random force chains. On the other hand, for water-saturated samples, which
showed a greater degree of linearity and little variability, the force chain model may not be applicable. Measurement
of the nonlinearity of water saturated sand was not straightforward. Experimental results will be shown.
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Nov 28
Dr. Philippe Blanc-Benon, Ecole Centrale de Lyon, Lyon, France
Particle Image Velocimetry and Temperature Measurements in Thermoacoustic Stacks
The knowledge of temperature and flow fields in the microchannels and at the edges of the stack plates becomes an
increasingly important issue in the design of heat exchangers for thermoacoustic engines. On these topics we have
conducted experiments in a resonant standing wave thermoacoustic refrigerator model. First, we present
experimental data obtained using Particle Image Velocimetry: velocity profiles across the microchannels, 2D velocity
maps including a zoom for the edges of the stack, and vorticity fields calculated with a criterion based on a
normalized angular momentum. Second, using a linear array made of miniature thermocouples, we measured the
build-up of the temperature gradient along the stack for different oscillating flow conditions. In particular the effect
of the plate spacing is illustrated. Finally, comparisons are made with theoretical models and numerical simulations
recently published in the literature.
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Nov 30
Dr. Philippe Blanc-Benon, Ecole Centrale de Lyon, Lyon, France
Scattering of Sound by a Core Vortex: Numerical Simulations Using a Wide-Angle Parabolic Equation
The generation and scattering of sound by flow inhomogeneities such as vortices are basic problems which have received
much attention in the efforts to develop methods to detect strength and location of noise sources. Recent experimental
studies have demonstrated that acoustic scattering can serve as an efficient (direct and nonintrusive)probe of the
vorticity field for the characterization of turbulent flows. In 1978 Candel presented the results of a numerical study
based on a standard parabolic equation in which the sound speed variations are included through an effective sound
speed c eff = c 0+ V x, where the x axis gives the direction of propagation of the acoustic wave. However, the effective
sound speed model does not include the effects of the perpendicular components of the velocity field, and the
importance of these components increases with the angle of propagation. A wide angle parabolic equation (WAPE)
has recently been proposed in order to increase the angular validity of the parabolic approximation. This equation
called MW-WAPE takes into account mean velocity effects up to second order in Mach number. To estimate the
validity of this new parabolic equation, we considered a configuration with both strong gradient and high Mach
number. Our results are compared to a reference solution obtained by solving the linearized Euler equations. The
MW-WAPE solutions are in good agreement with the reference solutions. This parabolic equation gives accurate
results up to M=0.5, whereas the standard parabolic equation using an effective sound speed failed to give good
results above M=0.2.
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