Acoustic Analogy Research Articles

Artificial Intelligence in Metamaterial Informatics for Sonic Frequency Mechanical Identification Tags

AbstractDesigning mechanical metamaterials to control wave propagation often requires extensive finite element analysis and discrete Fourier transform simulations before fabricating 3D printed structures and conducting experiments. Here, an alternative approach is presented to developing a metamaterial informatics framework by integrating dataset collection with artificial intelligence (AI), which can significantly accelerate the advancement of phononic wave chip technologies based on the triply periodic minimal surface (TPMS). Visualized data analysis is performed to evaluate the sensitivity of phononic band frequency numbers (BNF). Subsequently, various machine learning algorithms are compared for the prediction of sonic BNFs to create a unique identificable encoded mechanical identification tag (EMIT) interacting with sound waves. Then, for the mechanical decoding part with the help of acoustic analogy, a novel concept technology is developed that integrates 3D‐printed EMITs with a deep‐learning audio classifier for the ownership identification of instruments. Underwater application is discussed further for civil accident investigations, such as echolocating missing aircraft, divers, sunken ships, and containers with valuable cargo. These TPMS‐based EMITs represent the first‐generation passive sonic frequency identification (SFID) transponder‐tags, marking the advent of SFID transponder systems.

Split Control Wind Turbine Airfoil noise with CFD and Acoustic Analogies

Split Control Wind Turbine Airfoil noise with CFD and Acoustic Analogies

Numerical investigation of tip vortex cavitation noise with an emphasis on environmental nucleation effect

The multiscale interactions between macroscale cavities and microscale nuclei influence the tip vortex cavitation (TVC) dynamics and its induced noise. To study the underlying mechanisms, we employ a two-way transition and coupling Euler–Lagrange model. Through acoustic analogy analysis, we identify the cavity volume fluctuations as the main vocal mechanism of cavitating tip vortex, highlighting two critical cavity dynamics, i.e., the breathing mode of surface waves and the cavity collapse of downstream end. Multiscale simulation results suggest that the merging of microscale bubbles into macroscale cavities can generate a more continuous tip vortex cavity and enlarge the cavity size. In addition, the high-frequency noise is significantly increased due to the nuclei injection, and the cavity collapse noise is reduced due to a more continuous cavity. Our investigation provides a foundation for understanding multiscale TVC dynamics and noise.

Analysis of hydrodynamic performance and acoustic characteristics of loop propellers

To improve the efficiency and stealthiness of marine operations of autonomous underwater vehicles (AUVs), 12 loop propellers with different structural parameters are selected as research subjects. The Reynolds-averaged Navier–Stokes equations method is used to simulate the flow field result around the loop propellers and is combined with detached eddy simulation and the acoustic analogy method for hydrodynamic analysis and noise prediction. The influence of three structural parameters, namely the number of propeller blades, the thickness of propeller blades, and the pitch of propeller blades, on the hydrodynamic and noise performance of the propeller is investigated, and the loop propeller structure with the optimal hydrodynamic and noise performance is selected. The research results indicate that increasing the number of propeller blades and increasing the pitch of the loop propeller can significantly improve the thrust and torque of the propeller and effectively reduce the noise. However, increasing the thickness of the propeller blades can also increase the thrust and torque of the propeller, but it will sacrifice the noise performance of the loop propeller to a certain extent. The sensitivity of the noise performance with respect to the blade thickness is significantly higher than that of the two parameters of blade number and pitch. To verify the accuracy of the hydrodynamic and noise performance simulation results, this study conducted hydrodynamic and noise performance tests on the preferred loop propeller structure in the towing pool and anechoic pool and successfully verifies the reliability of the numerical simulation method used in this study for the prediction of the propeller performance by comparing the test data with the simulation results. This study provides theoretical support for the design optimization of loop propellers and helps to promote the design of high-efficiency and low-noise propellers in complex marine environments.

STUDY OF AERODYNAMIC NOISE OF PROPELLER CONSIDERING THE INFLUENCE OF BOUNDARY SURFACE USING CFD METHOD

This article focuses on the aerodynamic and acoustic characteristics of both an isolated propeller model and a propeller - boundary surface model. The study uses the Reynolds-averaged Navier-Stokes (RANS) method combined with Computational Fluid Dynamics techniques to analyze the flow field and wake flow behind the propeller and to determine its basic aerodynamic coefficients. The pressure on the surface of the propeller and boundary surface is used as input for the noise calculations. An acoustic analogy method, based on the Farassat 1A formulation derived from the Ffowcs Williams-Hawkings (FW-H) equation, is employed to calculate the propagation of noise from the surfaces of the propeller and boundary surface to designated positions (microphones). The research results lead to some significant conclusions drawn by the authors.

Near-field acoustic imaging with a caged bubble

Bubbles are ubiquitous in many research applications ranging from ultrasound imaging and drug delivery to the understanding of volcanic eruptions and water circulation in vascular plants. From an acoustic perspective, bubbles are resonant scatterers with remarkable properties, including a large scattering cross-section and strongly sub-wavelength dimensions. While it is known that the resonance properties of bubbles depend on their local environment, it remains challenging to probe this interaction at the single-bubble level due to the difficulty of manipulating a single resonating bubble in a liquid. Here, we confine a cubic bubble inside a cage using 3D printing technology, and we use this bubble as a local probe to perform scanning near-field acoustic microscopy—an acoustic analog of scanning near-field optical microscopy. By probing the acoustic interaction between a single resonating bubble and its local environment, we demonstrate near-field imaging of complex structures with a resolution that is two orders of magnitudes smaller than the wavelength of the acoustic field. As a potential application, our approach paves the way for the development of low-cost acoustic microscopes based on caged bubbles.

Analysis of the Vibration Effect on the Trailing Edge Noise for Wind Turbine Applications

The noise emitted is a factor in determining the location for installing wind turbines. It can be a concern for people living near wind farms due to the nuisance and health problems caused by noise emissions. Therefore, noise estimation is one of the most relevant aspects of wind turbine design. Aerodynamic noise can be caused by air motion around the turbine blades. This can create a swooshing or whooshing sound as the blades pass through the air. Aerodynamic noise tends to be more prominent at higher wind speeds when the turbine is operating at full capacity. The trailing edge noise is the main source of wind turbine aerodynamic noise. In this work, semi-analytical solutions for modeling this effect are used. The Ffowcs Williams and Hawkings (FW-H) acoustic analogy is used to predict far-field noise generated by wind turbine blades moving in the air. The equations of the rotor–tower–nacelle structure are obtained by the classical finite element method for a typical onshore wind turbine to predict the blade vibration signal. This new formulation is applied to rotating sources and statistical analysis of broadband trailing edge noise. The novelty of this work is to model the acoustic–structure interaction between the wind flow and the blade structure vibration. In this context, the acoustic far-field pressure emissions are modified by source vibration. In this point, this work compares the acoustic pressure values from rigid and flexible sources. Once the relationship between acoustic emission and wind turbine structural vibration is determined, the potential application of this research is, for example, to provide valuable information about the health and integrity of the blades. Thus, the goal of this work is to predict the aerodynamic noise of a typical large wind turbine taking into account its structural behavior. Therefore, Formulation 1A is used to calculate the far-field noise radiated from the trailing edge of wind turbine blades in a low Mach number flow. The vibration effects are input variables to evaluate the intensity and acoustic pressure values. Some computational aspects are discussed and the numerical model is clarified. The acoustic predictions are validated with analytical results and experimental measurements that are available in the scientific literature. The numerical results of the FW-H acoustic analogy demonstrate that the aerodynamic noise value is predominantly low frequency in the sections closest to the source.

Numerical investigation of noise reduction of a pump-jet propulsor using porous metal

A novel strategy for noise reduction in pump-jet propulsor (PJP) is proposed through the design of porous metal trailing edges on stator blades. The interference between stator wake vortices and rotor blades is one of the primary mechanisms for noise generation in PJP. The goal is to use a porous medium to diminish the intensity of turbulent vortices behind the stator blades, control the interaction between these shedding vortices and the rotor blades downstream of the stator, and ultimately suppress the rotor noise generation source. Large eddy simulation and acoustic analogy analysis of the entire propulsion system based on the Ffowcs-Williams and Hawkings equation are performed. It is found that with the use of porous stator trailing edges, the wake flow pattern of the stator is notably altered, the strong impact of the turbulent vortices on the rotor blades is weakened, and the wall pressure fluctuations on the rotor blades and duct are significantly reduced. As a result, the far-field radiation noise and tonal noise are both effectively reduced, with the maximum reduction in total and tonal sound pressure levels reaching 3.8 dB and 12.53 dB, respectively, corresponding to percentage reductions of 6.0% and 21.69%. These findings demonstrate that porous media have great potential for practical engineering applications in PJP noise control.

Prediction of splash noise in a rectangular tank under longitudinal periodic excitation

Sloshing phenomena within fuel tanks have emerged as a significant contributor to noise in hybrid and high-end vehicles, particularly as other sources of noise, such as those from the engine and transmission system, minimized. The manifestation of noise during sloshing results from the dynamic interplay between the fluid within the tank and both its surrounding structures and the fluid itself. “Splash noise” is an acoustic phenomenon which arises due to pressure fluctuations induced by fluid-fluid interactions during sloshing. Thus, the generation of splash noise encompasses a multi-physics process involving fluid flow and acoustic radiation. Accurate prediction of splash noise is crucial for implementing measures to mitigate it during the design phase. The current paper proposes a hybrid approach for predicting splash noise within a rectangular tank. The first step in the methodology is to predict the flow field within the tank, from which acoustic sources are computed. These sources are then utilized to calculate the sound propagation based on the acoustic analogy. To emulate a regime dominated by fluid-fluid interactions, periodic longitudinal excitations are imposed on the rectangular tank, both with and without baffles. Parameters such as fluid free-surface profile, tank wall pressures, and radiated sound pressure levels are systematically calculated and subsequently validated against experimental results available in the existing literature.

Volumetric and Entropic Sound Sources of Helmholtz Resonators with Different Temperatures

This study proposes an acoustic analogy model for the Helmholtz resonator (HR)–combustor system, considering the temperature difference between the bias flow from the HR and the grazing flow inside the combustor duct. The model highlights how the mass flux of the bias flow and the temperature difference serve as mass and entropic sound sources, respectively, influencing the HR’s sound absorption performance. To validate the model, we conducted numerical simulations using the Reynolds-averaged Navier–Stokes shear stress transport model to obtain the mean flow, followed by solving the frequency-domain linearized Navier–Stokes equations in COMSOL. The model was tested with HRs attached to combustor ducts under open–open and open–closed boundary conditions. Theoretical results agree well with numerical simulations, confirming the model’s accuracy. Results indicate that when the bias flow temperature is lower than the grazing flow temperature, the entropic sound source negatively affects duct acoustics, reducing sound absorption performance. Conversely, higher bias flow temperatures enhance sound absorption by superimposing entropic and mass-related sound sources. Additionally, the overall effect of the mass-related and entropic sound sources is equal to a volumetric source which depends on the mean sound speed and density of the HR instead of those of the combustor.

Effects of wall heating on wall pressure fluctuations and flow noise in a low-Reynolds-number turbulent channel flow with temperature-dependent viscosity

Wall pressure fluctuations and flow noise substantially degrade sonar detection performance and the acoustic stealth performance of underwater vehicles. This paper numerically investigates the effects of wall heating on wall pressure fluctuations in turbulent channel flow of water with temperature-dependent viscosity, exploring a novel method for controlling wall pressure fluctuations and flow noise in underwater vehicles. Large-eddy simulation (LES) is employed for the numerical calculation of the flow field, while a hybrid method combining LES with Lighthills acoustic analogy is employed to predict flow noise. The numerical results show that when the temperature difference between the wall and the incoming flow is 30 K and 50 K, the peak root-mean-square pressure fluctuations decrease by 6.76% and 8.91%, respectively. Wall heating stabilizes the pressure field near the wall, with the spectral levels of wall pressure fluctuations showing average decreases of approximately 1 dB and 2 dB. Wall heating weakens the energy-containing structures of wall pressure fluctuations and increases the overall convection velocity by 1.22% and 3.81%, respectively. Flow structure analysis reveals that the weakening of energy-containing structures results from the suppression of the vortex structures in the near-wall region. In the wall heating cases, peak turbulent kinetic energy decreases by 12.6% and 15.8%, respectively. Moreover, the sound pressure level of flow noise decreases with increasing wall temperature, with the maximum noise reduction exceeding 3 dB. Previous studies have not yet explored the effects of viscosity reduction caused by wall heating on wall pressure fluctuations and flow noise. This study demonstrates that wall heating is a promising method for reducing wall pressure fluctuations and flow noise.

Simulation and experimental research on the propagation mechanisms of acoustic energy inside the pipeline to detect the leakage

Leakage from pipelines has negative impacts on property and environment. The diameters of internal acoustic detectors in pipelines are small and not easily blocked, making it suitable for pipelines under various working conditions. Studying the characteristics of pipeline leakage sound signal and the propagation mechanisms within pipelines is crucial for timely detection of small leaks. In this study, a 3D simulation model of pipeline leakage was established, and a CFD/CAA hybrid calculation method was used to obtain effective leakage flow field information via LES. The equivalent sound sources in the flow field were extracted based on the Lighthill acoustic analogy theory. Determine the characteristic frequency range of the leakage sound signal was 1–2 kHz. This study founded that an increase in the leakage pressure and aperture size both lead to an enhancement in the leakage sound signal, and the propagation of leakage sound signal in pipelines is affected by background flow. An experimental pipeline leakage system was designed, and the accuracy of the simulation results was verified experimentally.

Acoustic pattern of a full scale simplified ship

Underwater radiated noise from ship propellers is one of the major contributors to the increase in overall noise levels in marine environments. The development of numerical tools for the computation of noise propagation is of paramount importance for the assessment of the noise impact on the environment. Hybrid approaches, based on the decoupling of the computation of the fluid flow and the successive evolution of the noise using an acoustic analogy, are typically conducted in open-water conditions, which do not correspond to a realistic environment. The Full Acoustic Analogy, which couples a propagation model based on the solution of the acoustic wave equation to the hybrid approach, enables the propagation of the noise generated by a marine propeller in a confined heterogeneous domain. The near-field scattering characteristics of a simplified hull positioned in front of a ship's propeller are analyzed in shallow and deep water, in the presence of the free surface, and compared to the open water case. The analysis determines the directivity of the propeller noise and how this may affect how the noise propagates in the marine environment.

A rapid aerodynamic noise prediction model for multi-rotor unmanned aircraft systems with inclusion of wake effect

In this work, the effect of wake on the rotor aerodynamics and aeroacosutics is studied based on an efficient rapid prediction model, which incorporates the induced effects of tip vortex on the blades into the blade element momentum theory. The tip vortex model is estimated using the free vortex wake method. The aerodynamic flow variables, as well as the unsteady loadings due to the radial flow and induction of tip vortices, are employed to model to equivalent sources and, therefore, noise emission, using Goldstein's acoustic analogy. The comparison between the hybrid algorithm and blade element momentum theory shows that the wake effect is not significant in the case of axial flow only. During forward flight conditions, the wake vortex correction greatly affects high frequency harmonics. In addition, a preliminary case study of a quad-rotor vehicle is also discussed, demonstrating the proposed low-fidelity computational framework is helpful for low-noise design and operation of the multi-rotor UAS vehicles.

Experimental observation of super-Klein tunneling in phononic crystals

We numerically and experimentally report the acoustic analogue of the super-Klein tunneling in a heterojunction of phononic crystals formed with Willis scatterers that exhibit pseudospin-1 Dirac cones. Pseudospin-1 Dirac cones are characterized by a triple states degeneracy in the band structure where two linear bands intersect with a flatband. The scattering properties of pseudospin-1 quasiparticles comprise an unity transmission through one potential barrier at its center frequency for all incident angles, which is called the super-Klein tunneling. In addition, the unity transmission does not depend on the barrier width. The Super-Klein tunneling differs from the conventional Klein tunneling, which consists of perfect transmission only under normal incidence through a potential barrier of any width. The Klein tunneling is predicted in pseudospin-1/2 systems like graphene, which are characterized by a two states degeneracy with two intersecting linear band. This direct observation in this acoustic analogue may have important implications in the exploration of the rich physics of pseudospin-1 quasiparticles.

A numerical analysis of isolated propeller noise using a lattice Boltzmann method approach

Current environmental needs to achieve carbon neutral commercial aviation by 2050 require the development of new technologies and aircraft configurations. Among the different technological developments proposed, the use of open fan or Ultra-High Bypass Ratio configurations is of interest due to their higher propulsive efficiency and performance. To support the development of such technologies, accurate and efficient tools early in the design stages are needed to predict aerodynamic performances and noise levels. One such tool is the lattice Boltzmann method, which can perform high-fidelity aeroacoustic simulations of flows around propellers and engines. The lattice Boltzmann approach can be advantageous over other numerical methods due to its easy integration with complex geometries, its low numerical dissipation properties, and its high level of computational efficiency. This paper presents the aerodynamic and aeroacoustic numerical study of an isolated propeller using the commercial lattice Boltzmann solver ProLB. Large Eddy Simulations were carried out using a compressible hybrid thermal version of the solver. An aeroacoustic analysis using a Ffowcs-Williams and Hawkings acoustic analogy for far-field noise was carried out. The objective is to assess the capabilities of the solver to predict acoustic emissions of an isolated propeller towards the future study of an installed case.

A basic study on sound insulation characteristics of Triply Periodic Minimal Surface by using the finite element method

Triply periodic minimal surfaces (TPMS) have garnered attention in the field of natural science. For example, these structures are observed in insect wing scales, where their intricate periodic structures create structural colors via the reflection and interference of certain wavelengths of light. The objective of this study is to utilize the acoustic analogy of such photonic properties for sound insulation. In a previous report, it was found that the bandgap of G-surface, which is one of TPMS, enabled us to insulate sound effectively at specific frequencies. Furthermore, it was suggested that sound insulation performance can be improved by compressing the structure along the incident direction while maintaining its thickness. In this paper, we focus on the P-surface, which is a typical TPMS other than the G-surface. The sound insulation properties were calculated by numerical analysis and compared with those of the G-surface. As a result, it is found that P- and G-surfaces are effective structures for different frequency bands. In addition, compression of the P-surface along the incident direction in the same manner as in the previous study improves the sound insulation performance without increasing the thickness, as well as G-surface.

Noise analysis of variable-speed rotor technology on the coaxial lift-offset helicopter

The impact of variable-speed rotor technology on the aerodynamic and aeroacoustic characteristics of a coaxial lift-offset helicopter was investigated using a numerical analysis approach. The free wake vortex lattice method was utilized to predict aerodynamic performance, while the Ffowcs-Williams Hawkings acoustic analogy was employed to evaluate the noise impact. The Harrington coaxial rotor was used as the baseline configuration. Results show that reducing the rotational speed, in combination with lift-offset, leads to a decrease in overall power required during forward flight by lowering both collective and cyclic pitch. This is primarily due to a reduction in profile power across the speed range. However, excessive rotor deceleration can lead to an expanded reverse flow region, increasing induced power at high forward speeds. From an acoustics perspective, the reduced rotor speed mitigated loading noise radiated toward the ground, especially in the region 40-60 degrees below the rotor plane, achieving a maximum 2.6 dB reduction at the evaluated observer location. This study indicates that the technology can offer advantages for both performance and noise in forward flight conditions.

Research on flow-induced radiated noise of twin-screw pumps based on the Lighthill acoustic analogue theory

Abstract To optimize the control of twin-screw pumps (TSP), it is essential to ensure performance while simultaneously preventing noise levels from exceeding specified limits. In order to investigate the flow characteristics and the mechanism of flow-induced radiated noise under various operating conditions, a coupled numerical simulation approach using Computational Fluid Dynamics (CFD) and Computational Acoustics (CA) was employed, and the findings were validated through experiments. The study reveals that the highest sound pressure levels of radiated noise occur near the rotor outlet surface, and the dynamic-static interference at the rotor-boundary interface is the primary cause of flow-induced noise in TSP. The flow-induced noise in TSP exhibits dipole characteristics, with the overall sound pressure level gradually increasing and then sharply rising with the increase in rotational speed (or flow rate). It stabilizes near the design operating point and continues to increase steadily with further increases in rotational speed (or flow rate). Modal testing using a dual-distributed measurement technique highlights significant interference effects between the rotor inlet and the dynamic rotor for the first two Blade Passing Frequencies (BPF) in TSP. The results of this study provide a theoretical foundation for the low-vibration and low-noise design and operation of TSP.

Super-resolution acoustic displacement metrology through topological pairs in orbital meta-atoms

The precise measurement of minute displacements using light is a common practice in modern science and technology. The utilization of sound for precision displacement metrology remains scarce due to the diffraction limit of half-wavelength, while it holds crucial applications in some specific scenarios, such as underwater environments, biological tissues, and complex machinery components. Here, we propose an approach to super-resolution acoustic displacement metrology by introducing the concept of topological pairs in orbital meta-atoms, drawing inspiration from the analogy of Cooper pairs observed in spinful electrons. The topological pairs are conjugately formed to create two distinct pathways in mode space that enable robust generation of interference. This allows the realization of acoustic analogue of Malus’s law and thereby enhances the resolution of displacement measurements. By incorporating a spiral twist configuration in orbital meta-atoms, we demonstrate the first acoustic prototype of a physical micrometer tailored for micron-scale displacement metrology. We observe experimentally a displacement resolving power of 1.2 μm at an audible frequency of 3.43 kHz, approximately 1/105 of the sound wavelength of 100 mm. Our work implies a new paradigm for precise displacement metrology within classical wave physics and lays the foundation for diverse acoustic applications.