Acoustic Velocity Field Research Articles

Observation of acoustic meron textures

Merons, as a member of quasiparticle family characterized by half-integer of the skyrmion topological charge with nontrivial topological textures, are of great interest in various branches of physics. Here, we report the first experimental observation of a meron texture configuration in acoustic waves. A squared metastructure is designed to support the spoof acoustic surface wave, forming meron lattice patterns in the acoustic velocity field vectors. The experimental results indicate that the meron textures can be moved and shaped by tuning the phase and amplitude differences between the excited sound sources, respectively. To demonstrate the topologically protected character of meron against structure defects, we further measure the acoustic pressure and velocity field distributions on a defective surface. The acoustic meron texture not only provides potential applications toward topologically robust ways to manipulate vectorial characteristics of the acoustic waves but also instills confidence for exploring other members of the quasiparticle family, such as the acoustic hopfion in acoustic waves.

Acoustic parameters and wave velocity field evolution characteristics in the high-stress region of granite

The risks of underground engineering originate from disturbances caused by the alterations to the stress field within rock masses. To understand the variations in the stress field within rock masses under local stress conditions, a set of double-hole pullout tests was used to design. The MS/AE location and tomography were used to investigate the evolution characteristics of the internal stress concentration area in granite. Results show that acoustic emission events transition from scattered and nucleated to regionally aggregated, then developing into arc-shaped patterns, ultimately exhibiting a trend of semi-spherical distribution. The increase in the fractal dimension of the spatial distribution of acoustic emission events indicates increased stress concentration degree, whereas a decrease signifies dispersion or transfer. Tomography results demonstrate the dynamic development process of local stress zones, with initial velocity anomalies as the core, continuously aggregating and expanding, showing an increasing difference trend compared to the velocity outside the region.

Acoustic Skyrmionic Mode Coupling and Transferring in a Chain of Subwavelength Metastructures.

Skyrmions, a stable topological vectorial textures characteristic with skyrmionic number, hold promise for advanced applications in information storage and transmission. While the dynamic motion control of skyrmions has been realized with various techniques in magnetics and optics, the manipulation of acoustic skyrmion has not been done. Here, the propagation and control of acoustic skyrmion along a chain of metastructures are shown. In coupled acoustic resonators made with Archimedes spiral channel, the skyrmion hybridization is found giving rise to bonding and antibonding skyrmionic modes. Furthermore, it is experimentally observed that the skyrmionic mode of acoustic velocity field distribution can be robustly transferred covering a long distance and almost no distortion of the skyrmion textures in a chain of metastructures, even if a structure defect is introduced in the travel path. The proposed localized acoustic skyrmionic mode coupling and propagating is expected in future applications for manipulating acoustic information storage and transfer.

Acoustic method Temperature and velocity fields in the furnace Co-measurement method study

Acoustic method Temperature and velocity fields in the furnace Co-measurement method study

Microparticle focusing and micromixing with two-dimensional acoustic waves

Acoustofluidics has recently been popularized as a crucial element of lab-on-a-chip (LoC) platforms to efficiently manipulate microparticles and continuous matter alike. In this study, a three-dimensional (3D) numerical model is proposed to simulate the focusing of polystyrene microparticles with three diameters and micromixing of dilute species using two orthogonally oriented standing waves, contrasting them with one-dimensional (1D) waves. The limiting velocity method is modified to explore the 3D acoustic streaming in a symmetric microchannel. In contrast to 1D standing acoustic waves, the simultaneous excitation of two orthogonal waves generates an acoustic streaming velocity field that does not counteract the radiation force. The obtained results show that the focusing efficiency of 5-μm particles reaches 97% with two dimensional (2D) standing acoustic waves, which was unachievable using 1D waves. Moreover, by reducing the flow rate to 1 μL min−1, the focusing of critical microparticle diameter peaked at 94%, indicating an approximately 9% improvement over a flow rate of 2.5 μL min−1. Increasing the viscosity of the background fluid resulted in 16% better 2D focusing with a single vortex compared to other cases, and higher amplitudes did not change focusing efficiency with a single vortex, while reducing efficiency in other cases. Finally, using 2D acoustic waves remarkably improved the mixing efficiency of dilute species, underscoring the advantage of 2D acoustic waves over their 1D counterpart. The proposed numerical model can play a meaningful role in cutting fabrication costs of next-generation LoC devices by identifying the most crucial parameters influencing acoustofluidic matter transport.

Clustering of passive tracers in a random acoustic velocity field

We consider the effects of passive tracer clustering (e.g., the magnetic field energy in stellar atmospheres) in a random acoustic velocity field. A method for numerical modeling of a two-dimensional random acoustic field is proposed. The field is described by a correlation tensor defined by traveling isotropic waves, taking into account dissipation. Two metrics for measuring the clustering effects are used: concentration and density. Using numerical modeling, we show that the tracer concentration is almost always clustered. The situation with the density is different; as the dissipation tends to zero, the time to reach the clustered states increases significantly. In addition, due to the tracer transport out of the density clustering regions, only a part of the tracer is clustered. For the presented analyses, we considered ensembles of Lagrangian particles and introduced and applied the statistical topography methodology.

Measured Regional Division Optimization for Acoustic Tomography Velocity Field Reconstruction in a Circular Area.

The acoustic tomography (AT) velocity field reconstruction technique has become a research hotspot in recent years due to its noninvasive nature, high accuracy, and real-time measurement advantages. However, most of the existing studies are limited to the reconstruction of the velocity field in a rectangular area, and there are very few studies on a circular area, mainly because the layout of acoustic transducers, selection of acoustic paths, and division of measured regions are more difficult in a circular area than in a rectangular area. Therefore, based on AT and using the reconstruction algorithm of the Markov function and singular value decomposition (MK-SVD), this paper proposes a measured regional division optimization algorithm for velocity field reconstruction in a circular area. First, an acoustic path distribution based on the multipath effect is designed to solve the problem of the limited emission angle of the acoustic transducer. On this basis, this paper proposes an adaptive optimization algorithm for measurement area division based on multiple sub-objectives. The steps are as follows: first, two optimization objectives, the condition number of coefficient matrix and the uniformity of acoustic path distribution, were designed. Then, the weights of each sub-objective are calculated using the coefficient of variation (CV). Finally, the measured regional division is optimized based on particle swarm optimization (PSO). The reconstruction effect of the algorithm and the anti-interference ability are verified through the reconstruction experiments of the model velocity field and the simulated velocity field.

Numerical modeling of a saxophone and comparison with experimental measurements

Saxophones making has long relied on craftsmanship, associated with an empirical knowledge of their acoustic functioning. The design process is now mainly based on the study of the input impedance, accessible experimentally or computationally. The numerical approaches are currently limited either by the accuracy (analytical models) or by the computation time (numerical resolution of PDEs). The challenge is to propose a numerical method combining both, to access the acoustic pressure and velocity fields in the instrument. Our objective was to develop a high-performance parallel numerical tool based on FEM to model accurately (a few cents on the resonances) the acoustic behavior of the resonator under playing conditions. The computation time was reduced by an order of magnitude compared to the brute force approach, using different modeling strategies specific to wind instruments: First, the modeling of the visco-thermal losses at the walls; then, the reduction of the size of the linear systems and finally, the reuse and model reduction to limit the effect of the multiple resolutions imposed by the wide frequency range of interest. The model is validated by comparison with experimental measurements. An impedance measurement system allowing acquisitions under controlled flow has been developed to reproduce realistic playing conditions.

Acoustics and aerodynamic effects following glottal and infraglottal medialization in an excised larynx model

ObjectiveThis study aimed to investigate the impact of the implant’s vertical location during Type 1 Thyroplasty (T1T) on acoustics and glottal aerodynamics using excised canine larynx model, providing insights into the optimal technique for treating unilateral vocal fold paralysis (UVFP).MethodsMeasurements were conducted in six excised canine larynges using Silastic implants. Two implant locations, glottal and infraglottal, were tested for each larynx at low and high subglottal pressure levels. Acoustic and intraglottal flow velocity field measurements were taken to assess vocal efficiency (VE), cepstral peak prominence (CPP), and the development of intraglottal vortices.ResultsThe results indicated that the implant's vertical location significantly influenced vocal efficiency (p = 0.045), with the infraglottal implant generally yielding higher VE values. The effect on CPP was not statistically significant (p = 0.234). Intraglottal velocity field measurements demonstrated larger glottal divergence angles and stronger vortices with the infraglottal implant.ConclusionThe findings suggest that medializing the paralyzed fold at the infraglottal level rather than the glottal level can lead to improved vocal efficiency. The observed larger divergence angles and stronger intraglottal vortices with infraglottal medialization may enhance voice outcomes in UVFP patients. These findings have important implications for optimizing T1T procedures and improving voice quality in individuals with UVFP. Further research is warranted to validate these results in clinical settings.

Spacetime geometry of acoustics and electromagnetism

Both acoustics and electromagnetism represent measurable fields in terms of dynamical potential fields. Electromagnetic force-fields form a spacetime bivector that is represented by a dynamical energy–momentum 4-vector potential field. Acoustic pressure and velocity fields form an energy–momentum density 4-vector field that is represented by a dynamical action scalar potential field. Surprisingly, standard field theory analyses of spin angular momentum based on these traditional potential representations contradict recent experiments, which motivates a careful reassessment of both theories. We analyze extensions of both theories that use the full geometric structure of spacetime to respect essential symmetries enforced by vacuum wave propagation. The resulting extensions are geometrically complete and phase-invariant (i.e., dual-symmetric) formulations that span all five grades of spacetime, with dynamical potentials and measurable fields spanning complementary grades that are related by a spacetime vector derivative (i.e., the quantum Dirac operator). These complete representations correct the equations of motion, energy–momentum tensors, forces experienced by probes, Lagrangian densities, and allowed gauge freedoms, while making manifest the deep structural connections to relativistic quantum field theories. Finally, we discuss the implications of these corrections to experimental tests.

Study of micro-scale flow characteristics under surface acoustic waves

As an effective tool for contactless manipulation of submicrometer scale objects, the controllability of acoustic streaming velocity and flow field morphology determines the accuracy of object migration and the completeness of three dimensional (3D) imaging. This paper proposes an equivalent acoustic streaming driving force model that is applicable to both two dimensional (2D) and 3D calculations and constructs a numerical method for submicrometer microsphere migration and rotation velocity in acoustic streaming. The results show that the relationship between the peripheral vortex size Lp/wc and the relative acoustic streaming velocity vas/vf satisfies Lp/wc = 0.125vas/vf0.36 under certain geometrical conditions. Reducing the spatial confinement and increasing the inter-vortex distance will increase the energy release efficiency, reduce the pressure gradient distribution and convective dissipation rates, increase the vortex intensity and radiation range, and consequently, increase the vortex characteristic size. In complex 3D vortex flow fields, suspended objects are affected by velocity distributions and exhibit motions such as cross-flow lines and rotation. For larger vortex structure sizes, full 3D imaging is more favorable due to the increased rotation speed and period of motion along the orbit of the submicrometer microspheres. This study helps us to reveal the modulation mechanism of acoustic streaming field flow characteristics, enrich the basic theory of alternating orbital motion and forces on objects in vortex structures, and provide guidance for acoustic flow-based contactless object manipulation.

Low-Mach number asymptotic analysis of fluid–structure-interaction (FSI) pressure waves inside an elastic tube

We consider the pressure wave having velocity cp inside an elastic tube of internal radius R0, thickness e, length L, shear modulus G and density ρs0, filled with a fluid with kinematic viscosity νf. We theoretically analyze the fluid–structure coupling between: (i) the elastic sheath, (ii) the fluid boundary layer, and (iii) the core acoustic pressure and velocity fields. Our analysis provides an asymptotic derivation of the fluid–structure-interactions (FSI) model that recovers known pulse-wave velocities and provides a new theoretical prediction for the exponential time decay of the wave longitudinal attenuation envelope. Taking advantage of highly distinct time-scales between the viscous radial diffusion τd=R02/νf compared with wave-convective time τc=L/cp as well as the elastic relaxation time τe=eρs/G, such that τe∼τc≪τd we perform a two time-scale asymptotic analysis based on a small parameter δ=τc/τd. Said parameter is obtained by balancing the momentum acceleration and the viscous damping rate in the inner unsteady boundary layer, the thickness of which being δR0. The resulting asymptotic sequence provides a unique consistent scaling for solid deformation and velocity fields, with the secularity condition associated with the leading-order slow-time scale envelope attenuation obtained by extending the analysis to investigate the first-order corrections.On the one hand our approach reconciles both predictions for the precursive elastic wave and the pulse velocities obtained when considering solid deformation only, and, on the other hand, predictions for the longitudinal attenuation resulting from the effect of boundary layers only. Our analysis also permits the derivation of a new convoluted model for the wall shear stress, which is (FSI)–consistent. The theoretical results are successfully compared with experimental measurements.

Flow structure and aerodynamic forces of finned cylinders during flow-induced acoustic resonance

This experimental study investigated the impact of self-excitation of acoustic resonance on the fluctuating lift force, flow structure, and aeroacoustic energy transfer of spirally finned cylinders with crimps in cross-flow. Three different finned cylinders with varying fin pitch-to-root diameter ratios (p/Dr) were compared with their equivalent diameter (Deq) bare cylinders. The study found that self-excitation of acoustic resonance occurred at a lower reduced flow velocity for the finned cylinders. During acoustic resonance excitation, finned cylinders with lower p/Dr experienced an abrupt increase in the fluctuating lift force coefficient and acoustic pressure. The decomposition of the fluctuating lift force with respect to the acoustic pressure showed that the earlier onset of resonance and the abrupt increase in the lift force and acoustic pressure were due to the increased susceptibility to flow-induced acoustic resonance. Phase-locked particle image velocimetry (PIV) measurements of the vorticity field supported this finding by showing a well-organized vorticity field in the wake of these finned cylinders. However, the fins and crimps had a significant effect on the distribution of the acoustic particle velocity field compared to the bare cylinder. The presence of the fins and crimps caused the acoustic particle velocity magnitude to be concentrated within the fins and rapidly decline away from the cylinder base. As a result, the acoustic power generated was lower in the case of the finned cylinders. This ultimately resulted in a lower peak acoustic pressure and fluctuating lift force being generated in the case of the crimped spirally finned cylinders.

An experimental transfer matrix method to characterize acoustic materials at high sound pressure levels in airflow environment

A transfer matrix method is proposed for experimental characterization of acoustic materials in the presence of airflow at high sound pressure levels. This method uses two experimental measurements with two different termination loads under flow to derive the transfer matrix coefficients of the tested material. The acoustic pressure and velocity fields upstream and downstream of the material are decomposed into forward and backward traveling waves. Complex models of the wavenumbers are used to account for the damping effect of acoustic waves in the presence of turbulent flow. The components of the transfer matrix of the material are given as function of the pressures and velocities at both faces of the material, which are obtained from the two measurements. The proposed method is validated by comparison with two-source method for different experimental measurements with airflow at high sound pressure levels up to 150 dB and good agreements are obtained. Thus, the proposed method can be used to estimate experimentally the acoustic properties of materials at higher sound pressure excitations in the presence of airflow.

Traveling of Oscillating Vortices and Its Thermal Effects in a Bending Channel

Abstract Driven by the periodical reverse of flow orientation, vortices in oscillatory flow induce a local high-speed and low-pressure flow region near the wall, which brings complex physical phenomena to viscous dissipation and heat transfer. This research focuses on the above-mentioned features by relating Spatio-temporal relationships between fluid dynamics and energy transmission. A two-dimensional oscillation model working in a thermoacoustic resonator is developed, considering heating and cooling processes in bending channels. We address oscillatory vortices' formation and transmission process in the bending channel. The acoustic streaming velocity field is obtained by postprocessing and proved to be the primary mechanism to induce spatial vortices in the vicinity of the entrance. The transferring vortices caused by the bending channel are like mini-pumps occupying fluid regions, which contribute to the local enhanced heat transfer performance and are influenced by the wall boundary conditions. The result also shows that skin friction in bending channels occupies about 10%–30% of total resistance, and the driving ratio is more sensitive to viscous dissipation than the wavy height of the bending channel. This study provides an approach to understanding the underlying mechanisms of heat transfer enhancement from hydrodynamics and inspiration to design compact heat exchangers employed in the oscillating flow.

Numerical Simulation on the Acoustic Streaming Driven Mixing in Ultrasonic Plasticizing of Thermoplastic Polymers.

The acoustic melt stream velocity field, total force, and trajectory of fluorescent particles in the plasticizing chamber were analyzed using finite element simulation to investigate the acoustic streaming and mixing characteristics in ultrasonic plasticization micro-injection molding (UPMIM). The fluorescence intensity of ultrasonic plasticized samples containing thermoplastic polymer powders and fluorescent particles was used to determine the correlation between UPMIM process parameters and melt mixing characteristics. The results confirm that the acoustic streaming driven mixing occurs in ultrasonic plasticization and could provide similar shear stirring performance as the screw in traditional extrusion/injection molding. It was found that ultrasonic vibrations can cause several melt vortices to develop in the plasticizing chamber, with the melt rotating around the center of the vortex. With increasing ultrasonic amplitude, the melt stream velocity was shown to increase while retaining the trace, which could be altered by modulating other parameters. The fluorescent particles are subjected to a two-order-of-magnitude stronger Stokes drag force than the acoustic radiation force. The average fluorescence intensity was found to be adversely related to the distance from the sonotrodes’ end surface, and fluorescence particles were more equally distributed at higher parameter levels.

On the acoustic performance of double degree of freedom helmholtz resonator based acoustic liners

This study investigates the acoustic performance of double degree of freedom Helmholtz resonators and multi cell acoustic liners made of these resonators, both experimentally and through finite element analysis. The dimensions of the resonator internal cavities were varied to assess the effect of the volume ratio on the acoustic performance of the system. Experiments were performed using a grazing flow impedance tube and instrumented 3D printed modular resonators, which can be switched between a single and double degree of freedom resonating cavity configuration. An aluminium acoustic liner with 16 modular resonating cavities was also used in experiments. The effect of the volume ratio is investigated by presenting the transmission loss and transmission coefficient induced and the changes in sound pressure level within the resonator. The underlying sound attenuation mechanisms are further elaborated through the finite element analysis results of the acoustic pressure and velocity fields in the different resonator configurations. The results showed that as the volume ratio is increased, the difference between the first and second resonance frequencies tends to have a convex behaviour. This may indicate the presence of an optimum volume ratio of the two internal cavities for a broad bandwidth of sound absorption. Moreover, the finite element analysis results showed that increasing the volume ratio increased both the transmission loss induced and the bandwidth of frequencies attenuated at the first resonance frequency due to an in-phase velocity magnitude relation, for both the neck and septum of the resonator. Conversely, for the second resonance frequency, there is an out-of-phase relation between the neck and septum velocity magnitudes. In addition to the single resonator analysis, the acoustic performance of liner configurations with 16 resonators was also investigated. The results showed an increase in the bandwidth of attenuated frequencies when each resonating cavity had a different volume ratio, as compared to a fixed volume ratio. In addition, the order of the resonators of different volume ratio in the liner arrangement did not seem to have a significant effect on the overall sound attenuation performance.

Spatially-varying impedance model for locally reacting acoustic liners at a high sound intensity

This paper is concerned with spatially-varying acoustic liner impedance in aeroacoustic ducts, in the presence of a high sound pressure level. It is shown that impedance discontinuity is a leading order parameter in the definition of the impedance variation. A large impedance discontinuity yields a high normal velocity variation, leading to significant nonlinear effects. An iterative numerical strategy is proposed to predict the spatially-varying acoustic impedance over a liner. A Bayesian inference process is coupled with a surrogate model to validate the model with measurements of the acoustic velocity fields above a liner at a high sound intensity, obtained using laser Doppler velocimetry.

Observation of Acoustic Skyrmions.

Despite a long history of studies, acoustic waves are generally regarded as spinless scalar waves, until recent research revealed their rich structures. Here, we report the experimental observation of skyrmion configurations in acoustic waves. We find that surface acoustic waves trapped by a designed hexagonal acoustic metasurface give rise to skyrmion lattice patterns in the dynamic acoustic velocity fields (i.e., the oscillating acoustic air flows). Using an acoustic velocity sensing technique, we directly visualize a Néel-type skyrmion configuration of the acoustic velocity fields. We further demonstrate, respectively, the controllability and robustness of the acoustic skyrmion lattices by tuning the phase differences between the acoustic sources and by introducing local perturbations in our setup. Our study unveils a fundamental acoustic phenomenon that may enable unprecedented manipulation of acoustic waves and may inspire future technologies including advanced acoustic tweezers for the control of small particles.

Hydrolysis acceleration in an Al-Ga-Gr particle material utilizing ultrasound irradiation.

The improvement of the hydrogen production rate and the hydrogen conversion ratio is crucial for hydrogen acquirement via Al-water reactions. Present work fabricated an Al-Ga-Gr hydrolyzing particle material, and presents the accelerated hydrolysis by ultrasound irradiation to achieve a high speed of hydrolysis and 100% yield within a short time, and provides a weak coupling model to address the acoustic pressure, velocity and thermal fields in the reactor. The obtained material is characterized with lamellar morphologies comprising AlGa solid solution and Gr. The hydrolysis is accelerated within the cavitation region by peeling off the reaction by-product layer to expose fresh aluminum, and deteriorates after the particle material traversing the cavitation/non-cavitation region boundary. Ultrasound promotes the hydrolysis progress from a diffusion governed mode to a dominated regime of interface reaction without a change to the activation energy.