Sound Generation Mechanism Research Articles

Acoustic Analogy for Multiphase or Multicomponent Flow

The Ffowcs Williams and Hawkings (FW-H) equation is widely used to predict sound generated from flow and its interaction with impermeable or permeable surfaces. Owing to the Heaviside function used, this equation assumes that sound only propagates outside the surface. In this paper, we develop a generalized acoustic analogy to account for sound generation and propagation both inside and outside the surface. The developed wave equation provides an efficient mathematical approach to predict sound generated from multiphase or multicomponent flow (MMF) and its interaction with solid boundaries. The developed wave equation also clearly interprets the physical mechanisms of sound generation, emphasizing that the monopole and dipole sources are dependent on the jump in physical quantities across the interface of MMF rather than the physical quantities on one-side surface expressed in the FW-H equation. The sound generated from gas bubbles in water is analyzed by the newly developed wave equation to investigate parameters affecting the acoustic power output, showing that the acoustic power feature concluded from the Crighton and Ffowcs Williams (C-FW) equation is only valid in a specific case of all bubbles oscillating in phase.

Nasal rustle: An evidence-based description, II

“Nasal rustle” (also known as “nasal turbulence”) is a loud nasal distortion that can be heard during speech production in certain children with velopharyngeal insufficiency (VPI). It occurs when there is a leak of airflow into the nasal cavity through a small velopharyngeal opening. While the perception of audible nasal emission—including nasal rustle—is a standard means for the diagnosis of VPI, there is no consensus on the sound generation mechanism. Current hypotheses include aerodynamic turbulence, velar flutter, and bubbling of mucus secretion. This study investigates the correlation between the acoustic signal of nasal rustle and physical movement at the superior velopharyngeal port. Several pediatric VPI patients were recorded via high-speed video nasopharyngoscopy and simultaneous nasometry during production of speech sounds susceptible to nasal rustle. Instances of perceived nasal rustle in the acoustic signal were identified and compared with the high-speed video. A high correlation was found between the bubbling frequency of mucus secretion above the velopharyngeal port and frequencies in the nasal acoustic signal, suggesting that secretion bubbling is a mechanism for generating nasal rustle. From this analysis, an integrated description of nasal rustle invoking physiological, physical, and acoustic principles is proposed.“Nasal rustle” (also known as “nasal turbulence”) is a loud nasal distortion that can be heard during speech production in certain children with velopharyngeal insufficiency (VPI). It occurs when there is a leak of airflow into the nasal cavity through a small velopharyngeal opening. While the perception of audible nasal emission—including nasal rustle—is a standard means for the diagnosis of VPI, there is no consensus on the sound generation mechanism. Current hypotheses include aerodynamic turbulence, velar flutter, and bubbling of mucus secretion. This study investigates the correlation between the acoustic signal of nasal rustle and physical movement at the superior velopharyngeal port. Several pediatric VPI patients were recorded via high-speed video nasopharyngoscopy and simultaneous nasometry during production of speech sounds susceptible to nasal rustle. Instances of perceived nasal rustle in the acoustic signal were identified and compared with the high-speed video. A high correlation was found b...

Nasal rustle: An evidence-based description

“Nasal rustle” (also known as “nasal turbulence”) is a loud nasal distortion that can be heard during speech production in certain children with velopharyngeal insufficiency (VPI). It occurs when there is a leak of airflow into the nasal cavity through a small velopharyngeal opening. While the perception of audible nasal emission—including nasal rustle—is a standard means for the diagnosis of VPI, there is no consensus on the sound generation mechanism. Current hypotheses include aerodynamic turbulence, velar flutter, and bubbling of mucus secretion. This study investigates the correlation between the acoustic signal of nasal rustle and physical movement at the superior velopharyngeal port. Several pediatric VPI patients were recorded via high-speed video nasopharyngoscopy and simultaneous nasometry during production of speech sounds susceptible to nasal rustle. Instances of perceived nasal rustle in the acoustic signal were identified and compared with the high-speed video. A high correlation was found between the bubbling frequency of mucus secretion above the velopharyngeal port and frequencies in the nasal acoustic signal, suggesting that secretion bubbling is a mechanism for generating nasal rustle. From this analysis, an integrated description of nasal rustle invoking physiological, physical, and acoustic principles is proposed.“Nasal rustle” (also known as “nasal turbulence”) is a loud nasal distortion that can be heard during speech production in certain children with velopharyngeal insufficiency (VPI). It occurs when there is a leak of airflow into the nasal cavity through a small velopharyngeal opening. While the perception of audible nasal emission—including nasal rustle—is a standard means for the diagnosis of VPI, there is no consensus on the sound generation mechanism. Current hypotheses include aerodynamic turbulence, velar flutter, and bubbling of mucus secretion. This study investigates the correlation between the acoustic signal of nasal rustle and physical movement at the superior velopharyngeal port. Several pediatric VPI patients were recorded via high-speed video nasopharyngoscopy and simultaneous nasometry during production of speech sounds susceptible to nasal rustle. Instances of perceived nasal rustle in the acoustic signal were identified and compared with the high-speed video. A high correlation was found b...

Aerodynamic Sound Production from Flying Beetles

The flapping wings of insects generate sounds during their flight. Recent interdisciplinary studies have extensively investigated the lift and thrust mechanisms produced from flapping flight; however, the associated sounds produced are less understood. Most studies have examined the amplitude and frequency with respect to wing beat reporting on the associated harmonic structure. The directionality and phase relationships have been examined in more detail in a few recent studies for flies and mosquitoes. In this study, we examine the sound generation mechanism from two invasive beetle species to Hawaii which are the Oriental Flower Beetle and the Coconut Rhinoceros Beetle. The wing beat, amplitude, and phase relationships are measured and determined with an eight element spherical microphone array. The mechanism of second harmonic generation for the different species is investigated with adaptive signal processing (Empirical Mode Decomposition) and complementary high speed optical video. The rotational motion of wing has a significant role in the second harmonic for the Coconut Rhinoceros Beetle. The different location and phase oscillation of the elytron for the two species results in different vortex generation during the down stroke.

Single-reed woodwinds: From physical modeling to sound radiation

Single-reed woodwind instruments have been traditionally used in marching bands, along with brass and percussion instruments. However their sound is often covered by louder instruments, making them less audible to the audience and the members of the band. Indeed, the saxophone has been designed in order to replace the clarinet in military bands, making the woodwind section of the band more prominent. This study discusses the sound generation mechanism of single-reed woodwind instruments in an attempt to investigate which reed and mouthpiece properties significantly affect the amplitude of the radiated sound. To this end, transfer function measurements and numerical investigations using physical modeling are employed. The former may indicate how the use of different mouthpiece geometries and various types of reeds may have an effect on the sound magnitude. The latter can be used to systematically vary reed and embouchure related parameters while observing how changes in these parameters affect the radiated sound.

Investigation of the sound generation mechanisms for in-duct orifice plates.

Sound generation due to an orifice plate in a hard-walled flow duct which is commonly used in air distribution systems (ADS) and flow meters is investigated. The aim is to provide an understanding of this noise generation mechanism based on measurements of the source pressure distribution over the orifice plate. A simple model based on Curle's acoustic analogy is described that relates the broadband in-duct sound field to the surface pressure cross spectrum on both sides of the orifice plate. This work describes careful measurements of the surface pressure cross spectrum over the orifice plate from which the surface pressure distribution and correlation length is deduced. This information is then used to predict the radiated in-duct sound field. Agreement within 3 dB between the predicted and directly measured sound fields is obtained, providing direct confirmation that the surface pressure fluctuations acting over the orifice plates are the main noise sources. Based on the developed model, the contributions to the sound field from different radial locations of the orifice plate are calculated. The surface pressure is shown to follow a U3.9 velocity scaling law and the area over which the surface sources are correlated follows a U1.8 velocity scaling law.

三味線の発音機構の解析 : 楽器音の立ち上がり部の波形と皮・駒・撥各部の振動波形の比較

三味線の発音機構の解析 : 楽器音の立ち上がり部の波形と皮・駒・撥各部の振動波形の比較

Acoustic characterization of wave energy converters

Wave energy converters produce sound as a consequence of their operation, but the specifics are not well-understood. Here, we present observations of two point-absorbing wave energy converters deployed at the US Navy’s Wave Energy Test Site in Kaneohe, HI. Measurements are obtained by free-drifting instrumentation packages which acoustical isolate the hydrophone from the surface expression to minimize masking by flow-noise (i.e., pseudo-sound generated by relative motion between hydrophone and water) and self-noise (i.e., propagating sound generated by the instrument package). Observations suggest that wave energy converters of different designs, even within the general class of point absorbers, produce different stereotypical sounds. Further, during normal operation, sound signatures can change substantially with sea state as new sound generation mechanisms come into play. One example of this is wave breaking around a shallow-hulled point absorber when waves exceed a critical steepness. The sound from bubble collapse is detectable up to several hundred kHz, whereas, below this critical steepness, wave converter sound is only detectable up to ten kHz. Finally, wave energy converter sounds are contextualized relative to other natural and anthropogenic sound sources to qualitatively explore their potential effects on marine animals.

Investigation of the flow- and sound-field of a low-pressure axial fan benchmark case using experimental and numerical methods

An extension of a benchmark case for a low-pressure axial fan is presented. The generic fan is a typical fan to be used in commercial applications. The fan design procedure, as well as the experimental setups are described in detail. The numerical approach is based on a forward coupling between a flow simulation with ANSYS Fluent and an aeroacoustic source term and wave propagation computation with multiphysics research software CFS + +. Experimental and numerical data for aerodynamics and aeroacoustics are compared. This includes aerodynamic performance (volume flow rate, pressure rise and efficiency), fluid mechanical quantities on the fan suction and pressure side (velocity distribution and turbulent kinetic energy), wall pressure fluctuations in the gap region and acoustic spectra at various microphone positions. Finally, a comprehensive data base of an axial fan was generated. Flow field properties at the fan suction and pressure side from the CFD simulation are in good agreement and spectra from the wall pressure fluctuations are in excellent agreement with the experimental data. Spectra from the computed acoustic pressure tend to slightly overestimate the experimental results. Based on the good agreement of both aerodynamic and aeroacoustic data, a thorough study on the dominant sound generation mechanisms is made.

Flame Quenching at Walls: A Source of Sound Generation

This paper presents a numerical study of head on quenching (HOQ) (an extreme case of flame/wall interactions) as a source of sound generation, which in turn can trigger combustion instabilities and enhanced noise levels. High-fidelity numerical simulations are performed to investigate the impact of wall temperature, high chamber pressures and Lewis number of the fuel on the noise generation. It is demonstrated by theory and simulations that the underlying mechanism of sound generation is flame surface destruction (flame annihila- tion). Special emphasis is put on chemical modeling where simple and complex mechanisms were compared: it is shown that simple chemistry simulations overestimate the generated pressure peaks due to a too fast extinction of the heat release rate compared to the complex scheme. In contrast to the simple mechanism, the complex scheme accounts for minor and intermediate species production and destruction which slows down the extinction process and thus lead to a lower sound level. This effect has to be taken into account, especially in the context of Large Eddy Simulation (LES) of combustion instabilities and combustion noise where simple chemical descriptions are often employed.

Scattering of turbulent-jet wavepackets by a swept trailing edge.

Installed jet noise is studied by means of a simplified configuration comprising a flat plate in the vicinity of a round jet. The effects of Mach number, jet-plate radial distance, and trailing-edge sweep angle are explored. Acoustic measurements are performed using a traversable 18-microphone azimuthal array, providing pressure data at 360 points on a cylindrical surface surrounding the jet-plate system. Key observations include a decrease, with increasing Mach number, of the relative level of the scattered field in comparison to the uninstalled jet; an exponential dependence of the scattered sound pressure level on the radial jet-plate separation; and considerable sideline noise reductions with increasing sweep angle, with which there is an overall reduction in acoustic efficiency. The measurements are compared with results obtained using a kinematic wavepacket source model, whose radiation is computed in two ways. A TGF for a semi-infinite flat plate is used to provide a low-order approximation of the scattering effect. Use of a more computationally intensive boundary element method provides additional precision. Good agreement between model predictions and experiment, encouraging from the perspective of low-cost prediction strategies, demonstrates that the models comprise the essential sound generation mechanisms.

Identification of jet noise source using causality method based on large-eddy simulation of a round jet flow

An acoustic analogy analysis based on a decomposition of the source term in Lighthill’s equation is discussed in light of a large-eddy simulation of a subsonic turbulent jet exhausting from a baseline round nozzle at Mach number M = 0.9 with Reynolds number Re = 105. The decomposed sub-terms show the nonlinear reciprocal interactions of density, velocity, vorticity, and dilatation fields. To understand the aerodynamic sound generation mechanism, intrinsic links between turbulent flow and emitted acoustic signals are made and applied to the large-eddy simulation data. Cross-correlation functions are used for the links between the far-field sound signals and the sub-terms as well as major flow variables in the jet flow domain. The spatial distributions of cross-correlations are examined to identify the sound source distribution throughout the domain and observe the mutual interactions and cancellations between the decomposed sub-terms. The contributions of sub-terms are also studied in frequency domain.

Multi-physics modeling of conformal, solid-state, and thin-film thermophones

Thin-film thermophones are thermoacoustic loudspeakers made from new materials such as aligned carbon nanotubes or graphene. They are solid state devices, in that there are no moving parts associated with the sound generation mechanism. Lumped parameter models have been developed for planar thermophones and agree well with experimental results. One benefit of thin-film thermophones is that they can be designed such that the transducer can be conformal to complex geometries. However, the lumped parameter models are not appropriate for complex geometries or electrical/thermal transients. An electrical-thermal-acoustic multiphysics model of these transducers has been created using COMSOL Multiphysics to address the issues present with the lumped parameter models. Development and validation of the model will be discussed.

Acoustic energy generation of “air-jet” instruments: Energy transfer between jet oscillation and acoustic field

In this talk, we discuss how to estimate the acoustic energy generation of “air-jet” instruments with numerical simulation. To attack this problem, we use Howe’s energy corollary, with which we can estimate energy transfer between unsteady flow, i.e., oscillating jet and acoustic field. To calculate Howe’s formula, we need solenoidal velocity of the flow and its vorticity together with acoustic particle velocity separated from the whole velocity of compressible fluid. Recently, a method, which allows us to approximately calculate Howe’s formula, was developed in experiments by Bamberger and Yoshikawa et al., and it can be applied for the numerical calculation. We apply the method for the numerical calculation of a flue organ pipe model. We also introduce a toy model of the oscillating jet to investigate the mechanism of sound generation from the oscillating jet in detail. The acoustic energy is mainly generated in the downstream of the oscillating jet near the edge of the mouth opening, but it is consumed in the upstream near the flue exit to synchronize the jet motion with it. Our results are in good agreement with the experimental result by Yoshikawa et al. as well as Howe’s theoretical prediction.

Standing wave acoustic levitation on an annular plate

In standing wave acoustic levitation technique, a standing wave is formed between a source and a reflector. Particles can be attracted towards pressure nodes in standing waves owing to a spring action through which particles can be suspended in air. This operation can be performed on continuous structures as well as in several numbers of axes. In this study an annular acoustic levitation arrangement is introduced. Design features of the arrangement are discussed in detail. Bending modes of the annular plate, known as the most efficient sound generation mechanism in such structures, are focused on. Several types of bending modes of the plate are simulated and evaluated by computer simulations. Waveguides are designed to amplify waves coming from sources of excitation, that are, transducers. With the right positioning of the reflector plate, standing waves are formed in the space between the annular vibrating plate and the reflector plate. Radiation forces are also predicted. It is demonstrated that small particles can be suspended in air at pressure nodes of the standing wave corresponding to a particular bending mode.

Hydroacoustic methods and tools for fish stock assessment and fishery maintenance Part 2. Methods and tools of fishery biohydroacoustics

Studies on influence of hydroacoustic fields on behaviour of commercial species and using of hydroacoustic tools for management of fish and squids behavior to increase the fishing efficiency are overviewed. The methods and means of fisheries biohydroacoustics are considered critically and the reasons of their unsatisfactory using in fishery are analyzed. Sounds with a certain spectrum and level are still applied for influence on fish behaviour without sufficient scientific and technical substantiation, so a complex approach to development of effective hydroacoustic tools for remote control of fish movement is necessary. Results of studies on acoustic reception and acoustic activity for schooling physostomous fishes are presented. Spectral-power and temporal parameters of the sounds and their frequency differentiation by fish size are determined. Sound-generating mechanisms of fish are considered and signal significances of the sounds radiated by fish are recognized. Stereotypes of acoustic behaviour are revealed for toothed whales during their hunting upon fish: these predatory cetaceans have special acoustic manipulators able to generate signals for concentration and holding the fish, adapted for hearing system of the prey. Results of hydrobionic modelling of organs and mechanisms for sound generation of marine animals and their technical realization in hydroacoustic devices are presented. The developed devices allow to generate underwater pulse sound signals simulating biological signals of certain physostomous fish species and predatory cetaceans (dolphins and killer whales). Efficiency of these simulating signals influence on behaviour of fish is proved by behavioral experiments and fishing tests. Applications of these devices for various fisheries are discussed.

G-14 産業車両の静粛性と熱管理に関する研究 : エンジンルームの換気方法の違いによる騒音発生機構の考察

G-14 産業車両の静粛性と熱管理に関する研究 : エンジンルームの換気方法の違いによる騒音発生機構の考察

水中気泡から放射される音の発生メカニズムについて

水中気泡から放射される音の発生メカニズムについて

Particle Image Velocimetry and Proper Orthogonal Decomposition Applied to Aerodynamic Sound Source Region Visualization in Organ Flue Pipe

AbstractThe paper presents experimental results of the visualization of the nonlinear aeroacoustic sound generation phenomena occurring in organ flue pipe. The phase-locked particle image velocimetry technique is applied to visualize the mixed velocity field in the transparent organ flue pipe model made from Plexiglas. Presented measurements were done using synchronization to the tone generated by the pipe itself sup- plied by controlled air flow with seeding particles. The time series of raw velocity field distribution images show nonlinear sound generation mechanisms: the large amplitude of deflection of the mean flue jet and vortex shedding in the region of pipe mouth. Proper Orthogonal Decomposition (POD) was then applied to the experimental data to separately visualize the mean mass flow, pulsating jet mass flow with vortices and also sound waves near the generation region as well as inside and outside of the pipe. The resulting POD spatial and temporal modes were used to approximate the acoustic velocity field behaviour at the pipe fundamental frequency. The temporal modes shapes are in a good agreement with the microphone pressure signal shape registered from a distance. Obtained decomposed spatial modes give interesting insight into sound generating region of the organ pipe and the transition area towards the pure acoustic field inside the resonance pipe. They can give qualitative and quantitative data to verify existing sound generation models used in Computational Fluid Dynamics (CFD) and Computational Aero-Acoustics (CAA).

Confinement of gigahertz sound and light in Tamm plasmon resonators

We demonstrate theoretically and by pump-probe picosecond acoustics experiments the simultaneous confinement of light and gigahertz sound in Tamm plasmon resonators, formed by depositing a thin layer of Au onto a GaAs/AlGaAs Bragg reflector. The cavity has InGaAs quantum dots (QDs) embedded at the maximum of the confined optical field in the first GaAs layer. The different sound generation and detection mechanisms are theoretically analyzed. It is shown that the Au layer absorption and the resonant excitation of the QDs are the more efficient light-sound transducers for the coupling of near-infrared light with the confined acoustic modes, while the displacement of the interfaces is the main back-action mechanism at these energies. The prospects for the compact realization of optomechanical resonators based on Tamm plasmon cavities are discussed.