Radiation modes of propeller tonal noise

2021 ◽  
pp. 1-25
Author(s):  
Hanbo Jiang ◽  
Siyang Zhong ◽  
Han Wu ◽  
Xin Zhang ◽  
Xun Huang ◽  
...  
Keyword(s):  
Spherical Harmonics ◽  
Sound Field ◽  
Low Noise ◽  
Noise Model ◽  
Sound Waves ◽  
Tonal Noise ◽  
Noise Sources ◽  
Separate Source ◽  
Radial Forces ◽  
Flow Variables

Abstract This paper focuses on the radiation modes and efficiency of propeller tonal noise. The thickness noise and loading noise model of propellers has been formulated in spherical coordinates, thereby simplifying numerical evaluation of the integral noise source. More importantly, the radiation field can be decomposed and projected to spherical harmonics, which can separate source-observer positions and enable an analysis of sound field structures. Thanks to the parity of spherical harmonics, the proposed model can mathematically explain the fact that thrusts only produce antisymmetric sound waves with respect to the rotating plane. In addition, the symmetric components of the noise field can be attributed to the thickness, as well as drags and radial forces acting on the propeller surface. The radiation efficiency of each mode decays rapidly as noise sources approach the rotating centre, suggesting the radial distribution of aerodynamic loadings should be carefully designed for low-noise propellers. The noise prediction model has been successfully applied to a drone propeller and achieved a reliable agreement with experimental measurements. The flow variables employed as an input of the noise computation were obtained with computational fluid dynamics (CFD), and the experimental data were measured in an anechoic chamber.

scholarly journals Research on Aerodynamic Noise Reduction for High-Speed Trains

2016 ◽  
Vol 2016 ◽  
pp. 1-21 ◽  
Author(s):  
Yadong Zhang ◽  
Jiye Zhang ◽  
Tian Li ◽  
Liang Zhang ◽  
Weihua Zhang
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Low Noise ◽  
Broadband Noise ◽  
Full Scale ◽  
Noise Model ◽  
Aerodynamic Noise ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Noise Sources

A broadband noise source model based on Lighthill’s acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES) using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H) acoustic analogy. An analysis of noise reduction methods based on the main noise sources was performed. An aerodynamic noise model for a full-scale high-speed train, including three coaches with six bogies, two inter-coach spacings, two windscreen wipers, and two pantographs, was established. Several low-noise design improvements for the high-speed train were identified, based primarily on the main noise sources; these improvements included the choice of the knuckle-downstream or knuckle-upstream pantograph orientation as well as different pantograph fairing structures, pantograph fairing installation positions, pantograph lifting configurations, inter-coach spacings, and bogie skirt boards. Based on the analysis, we designed a low-noise structure for a full-scale high-speed train with an average sound pressure level (SPL) 3.2 dB(A) lower than that of the original train. Thus, the noise reduction design goal was achieved. In addition, the accuracy of the aerodynamic noise calculation method was demonstrated via experimental wind tunnel tests.

Dual surface beamforming and acoustical holography for sound field visualization in reverberant environments

2009 ◽  
Vol 224 (1) ◽  
pp. 55-70 ◽  
Author(s):  
Yong Thung Cho ◽  
M J Roan ◽  
J Stuart Bolton
Keyword(s):  
Near Field ◽  
Sound Field ◽  
Field Measurements ◽  
Sound Waves ◽  
Noise Sources ◽  
Reflected Waves ◽  
Reverberant Environments ◽  
Reverberant Environment ◽  
Reflecting Surface ◽  
Acoustical Holography

Near-field acoustical holography is a technique that has been widely used to visualize noise sources from pressure measurements in spaces that can be assumed to be anechoic or semi-anechoic. Previously, a dual surface acoustical holography procedure based on making measurements on two surfaces between the source and a reflecting surface was introduced to remove the effects of reverberation. Little work has been performed in which beamforming has been used to visualize sources based on dual surface, near-field measurements in a reverberant environment: such a procedure is described here. Because many practical measurement environments are not completely anechoic, the source resolution accuracy of dual surface acoustical holography and beamforming procedures in reverberant environments is compared here by using numerical simulations. It has been found that dual surface acoustical holography provides the clearest representation of the source location when sound waves radiating from the source and the reflected waves are propagating in the opposite directions and when the measurement surfaces are conformal with the source geometry. However, it has also been found that dual surface beamforming provides more consistent source resolution performance regardless of the relative direction of wave propagation of the source and reflected waves.

scholarly journals Turbomachinery Noise Predictions: Present and Future

Acoustics ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 92-116 ◽  
Author(s):  
Stéphane Moreau
Keyword(s):  
Hybrid Methods ◽  
Free Field ◽  
Broadband Noise ◽  
Large Eddy Simulations ◽  
Analytical Models ◽  
Flat Plates ◽  
Tonal Noise ◽  
Noise Sources ◽  
Large Eddy ◽  
Rans Simulations

In future Ultra-High By-Pass Ratio turboengines, the turbomachinery noise (fan and turbine stages mainly) is expected to increase significantly. A review of analytical models and numerical methods to yield both tonal and broadband contributions of such noise sources is presented. The former rely on hybrid methods coupling gust response over very thin flat plates of finite chord length, either isolated or in cascade, and acoustic analogies in free-field and in a duct. The latter yields tonal noise with unsteady Reynolds-Averaged Navier–Stokes (u-RANS) simulations, and broadband noise with Large Eddy Simulations (LES). The analytical models are shown to provide good and fast first sound estimates at pre-design stages, and to easily separate the different noise sources. The u-RANS simulations are now able to give accurate estimates of tonal noise of the most complex asymmetric, heterogeneous fan-Outlet Guiding Vane (OGV) configurations. Wall-modeled LES on rescaled stage configurations have now been achieved on all components: a low-pressure compressor stage, a transonic high-pressure turbine stage and a fan-OGV configuration with good overall sound power level predictions for the latter. In this case, hybrid Lattice–Boltzmann/very large-eddy simulations also appear to be an excellent alternative to yield both contributions accurately at once.

Interaction between Strong Sound Waves and Cloud Droplets: Theoretical Analysis

2021 ◽  
Author(s):  
Ying-Hui Jia ◽  
Fang-Fang Li ◽  
Kun Fang ◽  
Guang-Qian Wang ◽  
Jun Qiu
Keyword(s):  
Sound Wave ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sound Field ◽  
Pressure Level ◽  
Velocity Variation ◽  
Time Range ◽  
Sound Waves ◽  
Cloud Droplets ◽  
Acoustic Frequency

AbstractRecently strong sound wave was proposed to enhance precipitation. The theoretical basis of this proposal has not been effectively studied either experimentally or theoretically. Based on the microscopic parameters of atmospheric cloud physics, this paper solved the complex nonlinear differential equation to show the movement characteristics of cloud droplets under the action of sound waves. The motion process of individual cloud droplet in a cloud layer in the acoustic field is discussed as well as the relative motion between two cloud droplets. The effects of different particle sizes and sound field characteristics on particle motion and collision are studied to analyze the dynamic effects of thunder-level sound waves on cloud droplets. The amplitude of velocity variation has positive correlation with Sound Pressure Level (SPL) and negative correlation with the frequency of the surrounding sound field. Under the action of low-frequency sound waves with sufficient intensity, individual cloud droplets could be forced to oscillate significantly. The droplet smaller than 40μm can be easily driven by sound waves of 50 Hz and 123.4 dB. The calculation of the collision process of two droplets reveals that the disorder of motion for polydisperse droplets is intensified, resulting in the broadening of the collision time range and spatial range. When the acoustic frequency is less than 100Hz (@ 123.4dB) or the Sound Pressure Level (SPL) is greater than 117.4dB (@ 50Hz), the sound wave can affect the collision of cloud droplets significantly. This study provides theoretical perspective of acoustic effect to the microphysics of atmospheric clouds.

scholarly journals Spiral Sound Wave Transducer Based on the Longitudinal Vibration

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3674 ◽  
Author(s):  
Wei Lu ◽  
Yu Lan ◽  
Rongzhen Guo ◽  
Qicheng Zhang ◽  
Shichang Li ◽  
...  
Keyword(s):  
Sound Wave ◽  
Longitudinal Vibration ◽  
Three Dimensional ◽  
Low Frequency ◽  
Sound Field ◽  
Field Measurements ◽  
Sound Waves ◽  
Underwater Sound ◽  
Three Dimensional Finite Element ◽  
Wave Transducer

A spiral sound wave transducer comprised of longitudinal vibrating elements has been proposed. This transducer was made from eight uniform radial distributed longitudinal vibrating elements, which could effectively generate low frequency underwater acoustic spiral waves. We discuss the production theory of spiral sound waves, which could be synthesized by two orthogonal acoustic dipoles with a phase difference of 90 degrees. The excitation voltage distribution of the transducer for emitting a spiral sound wave and the measurement method for the transducer is given. Three-dimensional finite element modeling (FEM)of the transducer was established for simulating the vibration modes and the acoustic characteristics of the transducers. Further, we fabricated a spiral sound wave transducer based on our design and simulations. It was found that the resonance frequency of the transducer was 10.8 kHz and that the transmitting voltage resonance was 140.5 dB. The underwater sound field measurements demonstrate that our designed transducer based on the longitudinal elements could successfully generate spiral sound waves.

scholarly journals Dredge-up by Sound Wave Emission from a Convective Core

1988 ◽  
Vol 108 ◽  
pp. 99-100
Author(s):  
Masa-aki Kondo
Keyword(s):  
Spherical Harmonics ◽  
Sound Wave ◽  
Sound Waves ◽  
Bottom Boundary ◽  
Ob Stars ◽  
Nonradial Oscillation ◽  
Convective Core ◽  
Propagation Zone ◽  
Wave Emission ◽  
Upper Boundary

Concerning the scattering of OB stars in the HR diagram (Humphry 1980), the effects of overshooting of convective core (Maeder 1984), mass loss (cf. chiosi and Maeder 1986), and generous stability criterion of semi-convection (Stothers and Chin 1976) have been discussed. Here, we will note the dredge up effect is caused by the sound waves emitted from a convective core.The sound mode of nonradial oscillation, with the spherical harmonics Ylm(θ, ϕ) and the frequency ω, can exist in the propagation zone, where the bottom boundary locates at the position of , and the upper boundary does near the photosphere. Here, Ll is called as the Lamb frequency, and cs is the sound velocity.

An Investigation on Numerical Simulation Method for Aero-Acoustics Based on Acoustics Analogy

2013 ◽  
Vol 444-445 ◽  
pp. 462-467
Author(s):  
Dang Guo Yang ◽  
Yong Hang Wu ◽  
Jin Min Liang ◽  
Jun Liu
Keyword(s):  
Numerical Simulation ◽  
Near Field ◽  
Time Lag ◽  
Sound Field ◽  
Leading Edge ◽  
Simulation Method ◽  
Three Dimension ◽  
Sound Waves ◽  
Acoustic Analogy ◽  
Numerical Simulation Method

A numerical simulation method on noise prediction, which incorporates aerodynamics and sound wave equations based on acoustic analogy, is presented in the paper. Near-field unsteady aerodynamic characteristic can be obtain by large eddy simulation (LES), and far-field propagation of sound waves and spatial sound-field can be obtain by solving the time-domain integral equations of Ffowcs Williams and Hawings (FW-H). Based on the method, a numerical simulation was done on a two-dimension cylinder and a three-dimension flat plate with blunt leading edge. The agreement of numerical results with experiment data validated the Feasibility of the method. The results also indicate that LES can describe vortex generation and shedding in the flow-fields, and FW-H formulation, which has taken time-lag between sound emission and reception times into account, can simulate time-effect of sound propagation toward far-fields.

A conjugate gradient least square based method for sound field control

2021 ◽  
Vol 263 (5) ◽  
pp. 1029-1040
Author(s):  
Pierangelo Libianchi ◽  
Finn T. Agerkvist ◽  
Elena Shabalina
Keyword(s):  
Conjugate Gradient ◽  
Regularization Parameter ◽  
Sound Field ◽  
Least Square ◽  
Active Set ◽  
Noise Sources ◽  
Field Control ◽  
Ill Posed ◽  
The Right ◽  
Number Of Iterations

In sound field control, a set of control sources is used to match the pressure field generated by noise sources but with opposite phase to reduce the total sound pressure level in a defined area commonly referred to as dark zone. This is usually an ill-posed problem. The approach presented here employs a subspace iterative method where the number of iterations acts as the regularization parameter and controls unwanted side radiation, i.e. side lobes. More iterations lead to less regularization and more side lobes. The number of iterations is controlled by problem-specific stopping criteria. Simulations show the increase of lobing with increased number of iterations. The solutions are analysed through projections on the basis provided by the source strength modes corresponding to the right singular vector of the transfer function matrix. These projections show how higher order pressure modes (left singular vectors) become dominant with larger number of iterations. Furthermore, an active-set type method provides the constraints on the amplitude of the solution which is not possible with the conjugate gradient least square algorithm alone.

scholarly journals Innovative passive multifrequency propeller device for noise and vibration reduction in turboprop fuselage

2018 ◽  
Vol 233 ◽  
pp. 00030 ◽  
Author(s):  
Angelo De Fenza ◽  
Maurizio Arena ◽  
Leonardo Lecce
Keyword(s):  
Noise Reduction ◽  
Tonal Noise ◽  
Research Activity ◽  
Noise Sources ◽  
Noise And Vibration ◽  
Aircraft Fuselage ◽  
Research Sector ◽  
Aeronautical Industry ◽  
Flight Regimes ◽  
Passive Noise

One of the main comfort issue affecting the passenger comfort into a turboprop aircraft fuselage is the propeller tonal noise and the related vibrations. It is well known that propeller rotation during flight generates the main noise sources, depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust and blades geometry. Thanks to the progress behind the control systems of the blades rotations, an innovative highly selective DVA has been conceived. The purpose of the research activity has been improving the performances of the standard passive tonal noise control system used for the BPF tuned noise and vibration attenuation in turboprop aircraft. Due to specific commercial need, the use of bi-tuned frequency can lead at a passive noise reduction at two RPM regimes. Generally, the turboprop aircrafts use only two RPM regimes: 100% at take-off, climb and approach, 86% during cruise, climb and descent. An innovative passive bi-tonal device capable to be tuned at two different frequencies in order to optimize the fuselage noise reduction at two different flight regimes (100% and 86%), has been designed and numerically verified. The functional effectiveness of the bi-frequential tuned device has been analysed by finite elements simulations on a linear beam, representative of the turboprop fuselage frame. The outcomes achieved within this activity encourage the advancement of this research sector, as a support to the needs of the turboprop aeronautical industry. According to the long experience gained by the research group, the proposed multifunctional concept can be a valid technology solution ready to be manufactured as well as validated in flight.

scholarly journals Jet-Surface Interaction Test: Phased Array Noise Source Localization Results

2012 ◽  
Author(s):  
Gary G. Podboy
Keyword(s):  
Source Localization ◽  
Phased Array ◽  
Noise Source ◽  
Jet Noise ◽  
Companion Paper ◽  
Far Field ◽  
Sound Waves ◽  
Axial Distribution ◽  
Noise Sources ◽  
Interaction Test

An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source localization measurements were obtained. This paper discusses phased array results, while a companion paper discusses far-field results. The phased array data show that the axial distribution of noise sources in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet noise to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet noise sources may satisfy this requirement.

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