Dominant Noise Source Research Articles

Smart Blade Count Selection to Align Modal Propagation Angle with Stator Stagger Angle for Low-Noise Ducted Fan Designs

The rotor–stator interaction noise is a major source of fan noise. Especially for low-speed fan stages, the tonal component is typically a dominant noise source. A challenge is to reduce this tonal noise, as it is typically perceived as unpleasant. Therefore, in this paper, we analytically, numerically and experimentally investigate an acoustic effect to lower the tonal noise excitation. Our study on an existing low-speed fan indicates a reduction in tonal interaction noise of more than 9 dB at the source if the excited acoustic modes propagate parallel to the stator leading edge angle. Moreover, a design-to-low-noise approach is demonstrated in order to apply this effect to two new fan stages with fewer stator than rotor blades. The acoustic design of both fans is determined by an appropriate choice of the rotor and stator blade numbers in order to align the modal propagation angle with the stator stagger angle. The blade geometries are obtained from aerodynamic optimization. Both fans provide similar aerodynamic but opposing acoustic radiation characteristics compared to the baseline fan and a significant tonal noise reduction resulting from the impact of the modal propagation angle on noise excitation. To ensure that this effect can also be applied to other low-speed fans, a design rule is derived and validated.

Noise Generated in a Scramjet Combustor

This paper presents the noise levels generated inside a two-dimensional scramjet combustor at Mach 7.3 freestream using the focused laser differential interferometric (FLDI) technique. FLDI measurements were taken at the front, middle, and rear of the combustor’s center plane under unfueled, combustion-suppressed, and combustion-on conditions. Spectral analysis of the FLDI signal shows density fluctuations inside the scramjet combustor are almost two times higher than the freestream and confirms the capability of this technique for measuring the disturbances in a complex hypersonic flowfield. Though combustion-induced pressure rise is low, a trend in the increase in the normalized density fluctuations/noise levels due to supersonic combustion is observed across the measurement locations for the combustion-on condition. However, the overall increment in the noise level is modest between the three conditions and across the three probing locations. This infers that, for the current scramjet geometry, fueling rates, fuel–air mixing, and supersonic combustion are not the dominant noise sources in the scramjet combustor. Instead, the base hypersonic flowfield inside the scramjet combustor is the main contributor to the noise field. Noting that there is relatively large uncertainty in the measured noise levels and that the combustion-induced pressure rise is modest in the present study, further investigation is needed to check the applicability of these results to the scramjet engines with flow paths having more complex flowfields, fueling schemes, and fueling rates.

Soundscape characterization in the Central Arctic Ocean ecosystem (Svalbard) using acoustic indices

An increasingly warmer, less frozen Arctic is opening further to vessel traffic, transforming dominant ambient noise sources in the underwater soundscape. Chief sources may be shifting from wind to ship noise. Collecting data that help explain the changing composition of the soundscape may offer insights to guide regulation of noise in the ocean, furthering management and conservation efforts. Hydrophones connected to field recorders were used in this study to characterize the soundscape and to study marine mammal presence and ship noise. Hydrophones were deployed at 44 locations from a 13.8 m Ovni 445 sailing vessel between 9° E and 19° E and 69° N and 80° N in April 2023. Acoustic indices were utilized to assess soundscape composition. Vessel locations were confirmed using Automatic Identification System (AIS) marine traffic data. Wind, waves, and ice (geophony) dominated the soundscape’s acoustic signature in remote locations, while human-caused sounds (anthrophony) were significant near Arctic shipping routes, fishing areas, and in fjords. Marine mammal vocalizations were detected near the ice edge, at fjord mouths, and in fjords. This acoustic characterization study provides a glimpse into the sonic sources and balance of sounds in the soundscape at present, essential data as the region rapidly transforms.

Trailing-edge far-field noise and noise source characterization in high inflow turbulence conditions.

Airframe noise currently is a bottle neck in various applications, e.g., wind energy, maritime applications, and aircraft. Airframe noise is significantly increased by the presence of inflow turbulence. High inflow turbulence influences the boundary layer and wall-pressure fluctuations close to the trailing edge of airfoils. In this research, measurements of boundary layer and wall-pressure fluctuations near the trailing edge of an airfoil are conducted to investigate how the inflow turbulence affects the trailing-edge noise generation mechanism. Far-field noise measurements of additional three airfoils are shown to understand the role of the airfoil geometry in the dominant noise source for the cases of inflow turbulence and to generalize the observed increase in trailing-edge noise. Inflow turbulence leads to an increase in both the wall-pressure spectrum and spanwise correlation length. Trailing-edge noise increases due to the inflow turbulence in the entire frequency range at least 2 dB up to more than 15 dB for all the cases. The contribution of leading- and trailing-edge noise to the total noise varies with the airfoil geometry and inflow velocity, with the trailing-edge noise dominating in a larger frequency range for the thickest airfoil and for lower velocities.

Compressed Gate Characterization for Quantum Devices with Time-Correlated Noise

As quantum devices make steady progress towards intermediate scale and fault-tolerant quantum computing, it is essential to develop rigorous and efficient measurement protocols that account for known sources of noise. Most existing quantum characterization protocols such as gate-set tomography and randomized benchmarking assume the noise acting on the qubits is Markovian. However, this assumption is often not valid, as for the case of 1/f charge noise or hyperfine nuclear spin noise. Here, we present a general framework for quantum process tomography (QPT) in the presence of time-correlated noise. We further introduce fidelity benchmarks that quantify the relative strength of different sources of Markovian and non-Markovian noise. As an application of our method, we perform a comparative theoretical and experimental analysis of silicon spin qubits. We first develop a detailed noise model that accounts for the dominant sources of noise and validate the model against experimental data. Applying our framework for time-correlated QPT, we find that the number of independent parameters needed to characterize one- and two-qubit gates can be compressed by 10× and 100×, respectively, when compared to the fully generic case. These compressions reduce the amount of tomographic measurements needed in experiment, while also significantly speeding up numerical simulations of noisy quantum circuit dynamics compared to time-dependent Hamiltonian simulation. Using this compressed noise model, we find good agreement between our theoretically predicted process fidelities and two-qubit interleaved randomized benchmarking fidelities of 99.8% measured in recent experiments on silicon spin qubits. More broadly, our formalism can be directly extended to develop efficient and scalable tuning protocols for high-fidelity control of large arrays of quantum devices with non-Markovian noise. Published by the American Physical Society 2024

Modeling Symmetric Coherent Mode Interactions in a Supersonic Rectangular Jet

This work presents the use of a reduced-order model (ROM) to predict coherent structure modes and their interaction with one another in a supersonic rectangular jet. The ROM formulation is unique in that it utilizes an integral technique and models the energy exchange between harmonically related modes, which can give insight on how to excite the jet in an experiment or computation. This ROM is used in conjunction with a linearized Euler equation solver to obtain shape functions for various disturbance frequencies. Work is limited here to symmetric modes of the coherent structure, and hence the disturbance in the upper and lower shear layers is in phase. Nonlinear solutions are first obtained without mode–mode interactions, giving a most amplified Strouhal number of 0.15 based on the height of the jet, which is assumed to be the dominant noise source in the jet, referred to as the fundamental frequency. The fundamental’s interaction with either the subharmonic or harmonic is assessed based on their ability to reduce the fundamental. Adding the harmonic is found to be more effective at reducing the peak of the fundamental, and thus this is concluded to be possibly an effective mechanism for noise reduction.

Analysis of direct and indirect noise in a next-generation aviation gas turbine combustor

A large-eddy simulation (LES) of a next-generation combustor is performed to examine effects of this combustor concepts on direct and indirect combustion noise characteristics. Direct noise is computed considering the unsteady heat release predictions while entropy fluctuations in the downstream part of the combustor are used to estimate indirect noise through the transfer function of the outlet nozzle. A low-order acoustic reconstruction technique, which utilizes the Green’s function of the configuration, is developed to compute the acoustics inside the combustor. Comparisons to experimental results are reported, showing the reasonable accuracy of the LES and combustion noise computations. The direct noise spectrum peaks at frequencies around 3 kHz because of the fast timescales associated with the chemical reactions inside the combustor. In addition, the indirect noise is dominant at low frequencies, i.e., less than 400 Hz, because of the characteristics of the entropy spectrum at the outlet nozzle. Compared to a conventional rich-quench-lean (RQL) combustor configuration, significant differences in the acoustics are observed, and are explained by two specific technological novelties. Firstly, the direct noise spectrum peaks at significantly higher frequencies due to the combustor’s compactness. Secondly, the entropy inhomogeneities downstream of the combustion region are an order of magnitude smaller in amplitude due to the lack of dilution with cold air. This leads to a significant reduction in the indirect noise amplitude at low frequencies, where it is the dominant source of noise. These results suggest opportunities for advanced combustion technologies to achieve substantial reductions in combustion-related noise.

Effects of elevated-temperature deposition on the atomic structure of amorphous Ta2O5 films

Brownian thermal noise as a result of mechanical loss in optical coatings will become the dominant source of noise at the most sensitive frequencies of ground-based gravitational-wave detectors. Experiments found, however, that a candidate material, amorphous Ta2O5, is unable to form an ultrastable glass and, consequently, to yield a film with significantly reduced mechanical loss through elevated-temperature deposition alone. X-ray scattering PDF measurements are carried out on films deposited and subsequently annealed at various temperatures. Inverse atomic modeling is used to analyze the short and medium range features in the atomic structure of these films. Furthermore, in silico deposition simulations of Ta2O5 are carried out at various substrate temperatures and an atomic level analysis of the growth at high temperatures is presented. It is observed that upon elevated-temperature deposition, short range features remain identical, whereas medium range order increases. After annealing, however, both the short and medium range orders of films deposited at different substrate temperatures are nearly identical. A discussion on the surface diffusion and glass transition temperatures indicates that future pursuits of ultrastable low-mechanical-loss films through elevated temperature deposition should focus on materials with a high surface mobility, and/or lower glass transition temperatures in the range of achievable deposition temperatueres.

Dynamic analysis and design of novel distributed lump-parameters mounting system for marine power devices

Marine power devices (MPD) are one of the dominant vibration and noise sources on board marine vessel. Its vibration can be attenuated effectively through floating raft mounting system. But this becomes unsuitable to implement due to a more stringent light-weighting request. In this paper, a novel distributed lump-parameters mounting system (NDLMS) for MPD is proposed consisting of two-stage mounting subsystem, attitude monitoring and controlling subsystem, and emergency protection subsystem. A theoretical model under multiple excitations is presented to estimate the vibration isolation effectiveness (VIE) using equivalent mobility matrix methods. To improve the VIE of NDLMS, distributed dynamic vibration absorbers (DDVA) are introduced. Compared with the equally weighted rigid mass blocks, DDVA has a qualitative improvement in the attenuation ability of the characteristic spectrum. Replacing part of the mass of mounting system with finely tuned DDVA can greatly reduce the vibration transmitted from vibratory MPD to the foundation. DDVA are validated to compensate for the vibration transmission loss by light-weighting. A scaled and a practical NDLMS prototypes are manufactured and tested. Experimental results validate the effectiveness of theoretical models and show that the performance of NDLMS satisfies the operation requirements of MPD.

Experimental and numerical investigation of the blade tip-related aeroacoustic sound source mechanisms of a ducted low-speed axial flow fan

A combined aerodynamic and aeroacoustic study of a ducted low-speed axial flow fan at various operating points is presented herein, focusing on the blade tip-related noise sources. The investigation includes upstream and downstream phased array microphone measurements and computational fluid dynamic simulations. The downstream acoustic measurements are carried out by using an acoustically transparent duct. The resulting flow fields and noise source maps are evaluated simultaneously. The results show that at higher flow rates, the dominant noise source is the turbulent boundary layer – trailing edge noise. At lower flow rates, the dominating noise sources can be found at the blade tip’s leading edge. These noise sources are found to be tip leakage flow related. Also, downstream microphone array measurements indicate strong noise sources at the blade tip’s trailing edge. These are determined to be a combination of the turbulent boundary layer - trailing edge noise, tip leakage vortex impingement noise, and double-leakage noise.

Experimental Parameters Influencing the Cavitation Noise of an Oscillating NACA0015 Hydrofoil

The strong increase in anthropogenic underwater noise has caused a growing intention to design quieter ships given that ship propellers are one of the dominating noise sources along the worldwide shipping routes. This creates an imminent demand for deeper knowledge on the noise generation mechanisms of propeller cavitation. A cavitating, oscillating two-dimensional NACA0015 hydrofoil is analyzed with hydrophone and high-speed video recording as a simplified and manipulatable representative of a propeller blade in a ship’s wake field for the identification of major influencing parameters on the radiated noise. A pneumatic drive allows the application of asymmetrical temporal courses of the angle of attack, a novel amendment to the widely reported sinusoidal setups. Three different courses are tested with various cavitation numbers. The combination of a moderate angle increase and a rapid decrease is found to generate significantly higher pressure peaks compared to symmetrical angular courses. Considering that the rapid change of the angle of attack caused by the inhomogeneous wake field behind the hull is the core of the cavitation occurrence, the understanding of its influence may contribute to the design of quieter ships in the future while still allowing for the necessary high propeller efficiency.

Mitigating Worst-case Exozodiacal Dust Structure in High-contrast Images of Earth-like Exoplanets

Detecting Earth-like exoplanets in direct images of nearby Sun-like systems brings a unique set of challenges that must be addressed in the early phases of designing a space-based direct imaging mission. In particular, these systems may contain exozodiacal dust, which is expected to be the dominant source of astrophysical noise. Previous work has shown that it may be feasible to subtract smooth, symmetric dust from observations; however, we do not expect exozodiacal dust to be perfectly smooth. Exozodiacal dust can be trapped into mean-motion resonances with planetary bodies, producing large-scale structures that orbit in lock with the planet. This dust can obscure the planet, complicate noise estimation, or be mistaken for a planetary body. Our ability to subtract these structures from high-contrast images of Earth-like exoplanets is not well understood. In this work, we investigate exozodi mitigation for Earth–Sun-like systems with significant mean-motion resonant disk structures. We find that applying a simple high-pass filter allows us to remove structured exozodi to the Poisson noise limit for systems with inclinations <60° and up to 100 zodis. However, subtracting exozodiacal disk structures from edge-on systems may be challenging, except for cases with densities <5 zodis. For systems with three times the dust of the solar system, which is the median of the best fit to survey data in the habitable zones of nearby Sun-like stars, this method shows promising results for mitigating exozodiacal dust in future Habitable Worlds Observatory observations, even if the dust exhibits significant mean-motion resonance structure.

The Effect of Conduit Walls Roughness on Volcanic Jets and Their Seismo‐Acoustic Radiation: An Experimental Investigation

AbstractTo explore the effect of conduit roughness on volcanic jet dynamics and on the related seismo‐acoustic radiation we performed a series of shock‐tube experiments using pipes with variable inner surface fractal dimension D. Variable starting pressure produced subsonic to supersonic jets visualized using high‐speed shadowgraph and recorded with an array of accelerometers and microphones. At all starting pressures, increasing D increases the energy transfer from the gas to the conduit walls, decreasing the jet exit velocity (Mach number) and, for supersonic cases, the related shock‐cell spacing, and increasing the seismic to acoustic radiation amplitude ratio. The roughness‐induced changes in jet velocity and turbulence affect the dominant sources of the jet noise and modulates the spectral properties of the acoustic signals. From our study we show that conduit wall roughness is an important and yet largely neglected factor in the dynamics of explosive volcanic eruptions and their monitored geophysical signals.

Contribution of jet flow noise sources to the far-field sound power

Jet noise is the dominant source of noise during aircraft takeoff. This study uses direct numerical simulation (DNS) data of subsonic jet flow obtained from computational fluid dynamics (CFD) simulations to perform acoustic analyses. The non-negative contribution technique (NNC) is employed to identify aeroacoustic sources of jet noise with the greatest contribution to far-field sound power. The NNC technique uses the Lighthill source distribution with an acoustic impedance matrix constructed from radiation kernels of the free-field Green’s function. The fast multipole method (FMM) is integrated with the NNC technique to reduce computational cost arising from decomposition of the acoustic impedance matrix as well as from the high number of CFD grids associated with the DNS data. The results showed that the dominant aeroacoustic sources are associated with the first component of the Lighthill tensor (T11) and are concentrated along the jet centerline, downstream of the nozzle exit.

Toward a general model for the evolution of the auditory sensitivity under variable ambient noise conditionsa).

Ambient noise constrains the evolution of acoustic signals and hearing. An earlier fitness model showed that the trade-off between sound detection and recognition helps predict the best level of auditory sensitivity for acoustic communication in noise. Here, the early model is improved to investigate the effects of different noise masking conditions and signal-to-noise ratios (SNRs). It is revealed that low sensitivity is expected for acoustic communication over short distances in complex noisy environments provided missed sound recognition is costly. By contrast, high sensitivity is expected for acoustic communication over long distances in quieter habitats or when sounds are received with good SNRs under unfavorable noise conditions. High sensitivity is also expected in noisy environments characterized by one dominant source of noise with a fairly constant spectrum (running-water noise) or when sounds are processed using anti-masking strategies favoring the detection and recognition of sound embedded in noise. These predictions help explain unexpected findings that do not fit with the current view on the effects of environmental selection on signal and sensitivity. Model predictions are compared with those of models of signal detection in noisy conditions and results of empirical studies.

A review of sound radiated by breaking ocean waves

“Physical Mechanisms of Noise Generation by Breaking Waves—A Laboratory Study” was published over 35 years ago by Mike Banner and Doug Cato. This seminal work describes a laboratory experiment demonstrating that the dominant source of breaking wave noise above a few hundred Hz is associated with the formation of bubbles and coalescing or splitting bubbles. This observation opened the door to explaining the properties of ambient sound under wind-driven seas and remotely monitoring air entrainment by breaking waves. Progress on these topics since Banner and Catos’ experiment will be reviewed and outstanding issues discussed. [Work supported by the US Office of Naval Research Ocean Acoustics program (Grant No. N00014-21-1-2316).]

Differential phase-diversity electrooptic modulator for cancellation of fiber dispersion and laser noise

Bandwidth and noise are fundamental considerations in all communication and signal processing systems. The group-velocity dispersion of optical fibers creates nulls in their frequency response, limiting the bandwidth and hence the temporal response of communication and signal processing systems. Intensity noise is often the dominant optical noise source for semiconductor lasers in data communication. In this paper, we propose and demonstrate a class of electrooptic modulators that is capable of mitigating both of these problems. The modulator, fabricated in thin-film lithium niobate, simultaneously achieves phase diversity and differential operations. The former compensates for the fiber’s dispersion penalty, while the latter overcomes intensity noise and other common mode fluctuations. Applications of the so-called four-phase electrooptic modulator in time-stretch data acquisition and in optical communication are demonstrated.

Mechanism of noise reduction caused by thickening top plate for high-speed railway box-girder bridge

For the high-speed railway concrete box-girder bridge, thickening the top plate can effectively reduce the structural noise radiation caused by moving trains. However, the noise reduction mechanism for thickening top plate has not been investigated. This mechanism is systematically studied in this paper by employing a train-track-bridge spatially coupled dynamics model and an acoustics boundary element model of the box-girder bridge. The results demonstrate that the top plate is the dominant noise source for the concrete box-girder bridge. Thickening top plate can significantly reduce the noise radiation capacity of the box-girder bridge, mainly through three mechanisms: (1) reducing the local modal shapes and vibrations of top plate, (2) decreasing the acoustic radiation efficiency, and (3) redistributing the train-induced vibration in the bridge. Furthermore, these three aspects collectively determine the total amount and spatial distribution of the noise radiation from the box-girder bridge due to moving trains. It is crucial to comprehensively these three aspects for the low-noise design of box-girder bridge.

Experimental and predicted leading- and trailing-edge noise of symmetric airfoils under zero mean-loading

Incorporating the effect of airfoil geometry in airfoil noise prediction methods is paramount to designing silent wind turbines and achieving regulation limits. However, the airfoil geometry effect on the leading- and trailing-edge noise has not been fully understood. To address this, our research uses a phased microphone array to measure the leading- and trailing-edge noise of airfoils NACA 0012, 00018, 0008, and 63018, which have different chord lengths. The inflow turbulence is generated by a rod located upstream of the airfoils. The far-field noise is compared with Amiet's theory for both noise sources. The results show that the leading-edge noise reduces with the leading-edge radius and maximum thickness in the high- and mid-frequency ranges, respectively. Scaling laws based on these geometric parameters are proposed. The trailing-edge noise of the several airfoils was compared at several velocities and Reynolds numbers. Scaling laws using these quantities were proposed for each case. Furthermore, the competition of leading- and trailing-edge noise mechanisms are assessed when airfoils are subjected to inflow turbulence. The dominant noise source varies in function of the airfoil geometry and frequency. The inflow turbulence increases the trailing-edge noise of the different airfoils. Furthermore, it dominates in a larger frequency range for the thickest airfoil.

Identification and Analysis of Noise Sources of Permanent Magnet Synchronous Traction Motor with Interior Permanent Magnet

The rapid development of electromobility is placing ever higher demands on new electric motor designs. This results in a gradual reduction in weight with a simultaneous increase in maximum torque. As a result, unfavorable phenomena, such as vibration and noise, can become apparent in the drivetrain. Modeling and evaluation of the acoustic noise sources of a traction motor are particularly important when it is used, for example, as the traction drive of an electric bus, where too high noise levels can have a negative impact on passengers. This article describes methods for analyzing and evaluating the root causes of noise that occurs in permanent magnet traction motors with a rotor in which the magnets have been placed inside the rotor (PMSM IPM). This paper presents an analysis of acoustic noise and forces acting in the air gap of a 240 kW motor with 60 stator slots and 2p = 10 (s60p20) as the number of pole pairs designed for bus and truck drives. To determine the dominant noise sources and evaluate their value, the forces acting in the air gap and their effect on the deflection of the outer surface of the stator yoke were calculated. The natural frequencies of the machine, their frequencies for the entire rotor speed range, and the frequency of vibration of the motor stator were calculated. Based on these data, the sound power level (A-SWL) was calculated at varying motor speeds. MANATEE software (EOMYS, 9, avenue de la Créativité, 59650 Villeneuve d’Ascq—FRANCE) from EOMYS was used to perform vibroacoustic calculations. The analysis results were also subjected to verification on a laboratory bench.