 Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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- Simulations of multi-rotor interaction noise at hovering & forward
flight conditions-
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Authors: Samuel O Afari, Reda R Mankbadi
Abstract: International Journal of Aeroacoustics, Ahead of Print.
A high-fidelity simulation of two in-line counter-rotating propellers in hover, and in forward flight conditions are performed. Near field flow and acoustic properties were resolved using Hybrid LES-Unsteady RANS. Far-field sound predictions were performed using Ffowcs-Williams-Hawkings formulation. The two-propeller results in hovering are compared with that of the single propeller. This enabled us to identify the aerodynamic changes resulting from the proximity of the two propellers to each other and to understand the mechanisms causing the changes in the radiated sound. We then considered the forward flight case and compared it with the corresponding hovering case. This enabled us to identify the aerodynamic changes resulting from the incoming stream. By examining the near acoustic field, the far-field spectra, the Spectral Proper Orthogonal Decomposition, and by conducting periodic averaging, we were able to identify the sources of the changes to the observed tonal and broadband noise.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-20T09:55:23Z
DOI: 10.1177/1475472X231152608
- Investigations of thickness effects on the acoustic characteristics of
symmetric and asymmetric airfoils-
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Authors: Sujit Kumar, Priyanshu Mishra, S Narayanan
Abstract: International Journal of Aeroacoustics, Ahead of Print.
The present paper provides a detailed acoustic characterization of symmetric and asymmetric NACA airfoils for various thickness ratios to determine the best thickness ratio and geometry which provide lower acoustic radiations with respect to the standard NACA0010 airfoil. The studies are conducted for various t/c values of 0.12, 0.15 and 0.21, where t is the airfoil thickness and c is the airfoil chord. The far-field acoustic emissions are observed to decrease with increase in t/c ratios for both the symmetric and asymmetric airfoils. For all the t/c values and jet velocities studied, the asymmetric airfoils show higher noise reductions from mid to high frequencies as compared to the symmetric ones, which might be due to the reduced transverse velocity fluctuations as a result of the large distortions imparted to oncoming turbulent gust by the formation of the larger stagnation pressure zone. The symmetric airfoils show a maximum reduction up to 3 dB from mid to high frequencies while asymmetric ones show a reduction up to about 5 dB. An empirical expression is developed for the ΔOAPWL as a function of t/c only for both the symmetric and asymmetric airfoils, where ΔOAPWL is the overall sound power reduction level in dB. It reveals that the ΔOAPWL follow a second order polynomial for both the symmetric and asymmetric airfoils at all jet velocities studied. It is observed that thicker (i.e., t/c = 0.21) symmetric and asymmetric airfoils show lower acoustic radiations as compared to the thinner ones for all the emission angles. In general, it is observed that the thinner airfoils show higher directivity as compared thicker ones, albeit they show a common trait of downstream directivity. Further the highest directivity is seen at an emission angle of 67.5° for both the symmetric and asymmetric airfoils. Thus, the present study clearly demonstrates that the airfoils with higher t/c ratios could be considered as the best passive means for achieving substantial reductions of airfoil broadband noise over a wide range of frequencies.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-17T06:13:10Z
DOI: 10.1177/1475472X231152607
- Playing flute without lips' Tones of music lost in time:An
investigation of the indigenous Bastar flutes of India-
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Authors: Ashish Karn, Ritvik Anand, Aditya Kataria, Ramesh Kumar Donga, Naman Agarwal, Varun Pratap Singh
Abstract: International Journal of Aeroacoustics, Ahead of Print.
The physics of music has been well studied and has provided the basis on which musical instruments are made, studied and characterized. Significant research has been conducted on the different kinds of musical instruments, which range from traditional instruments like the mridangas of India to the bagpipes of Scotland. In fact, a lot of research has been carried on the acoustics of different kinds of flutes as well, such as the Finnish kantele and the Indonesian Kompangs. The Indian subcontinent, the birthplace of transverse flutes and a host of other instruments, itself has a plethora of unique musical instruments that have been scientifically examined. Yet, the Bastar flutes of India have evaded the due scientific attention that they deserve owing to their unique sound generation mechanism. Quite strangely and surprisingly, these Bastar flutes are a unique genre of flutes that don’t require lips to be played, and are quite intriguing. The current research explores the aeroacoustics of a Bastar flute via experimental measurements, computational simulations and analytical formulations. The results demonstrate that the amplitude produced is directly proportional to the number of rims present. This are also responsible for producing a low-frequency, high-amplitude melodious sound. It also suggests that the underlying mechanism behind sound generation in a Bastar flute is a unique blend of edge tone and a jet tone, demonstrating a rare phenomenon not seen in traditional musical instruments. This uncommon phenomenon has the potential to unlock several new applications in the field of acoustics.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-11T08:30:10Z
DOI: 10.1177/1475472X221150176
- Angle-of-attack and mach number effects on the aeroacoustics of an SD7003
airfoil at Reynolds number 60,000-
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Authors: Dhanush Vittal-Shenoy, Romain Gojon, Thierry Jardin, Marc C. Jacob
Abstract: International Journal of Aeroacoustics, Ahead of Print.
The aeroacoustics of an SD7003 airfoil at Reynolds number 60,000 is investigated using Large Eddy Simulation. Five simulations are performed to study the effects of angle-of-attack and Mach number at fixed Reynolds number. For the three cases with angle-of-attack equal to 0° (M = 0.1, 0.3 and 0.6), a pure tonal noise associated with a 2D organisation of the flow is obtained. This flow topology is due to the establishment of a well known aeroacoustic feedback loop between the separation point on the suction side of the airfoil and the trailing edge. The occurrence of this loop is corroborated by the presence of a standing wave pattern with characteristic mode number in accordance with Panda’s model. The main effect of the Mach number is to promote flow separation and hence increase separation length and mode number. In addition, the first harmonic and the sub-harmonic of the tone, observed in the far field acoustic spectrum, are found to be generated in the wake, presumably due to non-linear vortex interactions. For the two other angles-of-attack 4° and 8° at M = 0.1, the feedback loop does not establish and a Laminar Separation Bubble (LSB) is observed. When increasing the angle-of-attack, the LSB shrinks with earlier reattachment. For those two cases, far-field spectra are characterized by a low frequency associated with the breathing motion of the LSB and the reattachment point fluctuating in space. The frequency of this fluctuation depends on the curvature of the bubble. Far-field spectra are also characterized by a broadband trailing edge noise whose frequency range decreases with the angle-of-attack. Again, this evolution is found to depend on the curvature of the bubble which may promote a centrifugal instability in the separated shear layer.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-10T02:07:52Z
DOI: 10.1177/1475472X221150173
- Numerical and experimental analysis of the influence of solidity on rotor
aeroacoustics at low Reynolds numbers-
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Authors: Thierry Jardin, Romain Gojon, Nicolas Doué, Hélène Parisot-Dupuis
Abstract: International Journal of Aeroacoustics, Ahead of Print.
We compare medium and high fidelity numerical simulations to experiments conducted on low Reynolds number rotors typical of small scale Unmanned Aircraft Systems (UAS). We first show that these numerical approaches provide reasonable estimates of the aerodynamic performance and farfield tonal noise and hence apply them for the investigation of the influence of solidity ratio on the aerodynamics and acoustics of small scale rotors operating under hovering, iso-thrust conditions. We show that while solidity ratio has a weak impact on aerodynamic performance, it may help drastically reduce farfield tonal noise. This reduction is however found to depend on the interplay between thickness and loading noise such that increasing the solidity by increasing the number of blades at constant blades’ aspect ratio or by decreasing the blades’ aspect ratio keeping the number of blades constant may yield very different, sometimes opposite, trends.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-09T05:11:44Z
DOI: 10.1177/1475472X221150181
- Aeroacoustic characteristics of supersonic offset jets
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Authors: Harinath Reddy Nakkala, K Srinivasan
Abstract: International Journal of Aeroacoustics, Ahead of Print.
The offset jet configuration is one where the jet is discharged at some distance from a solid surface. Although the geometric configuration may look simple, the flow may involve several complexities. In propulsion systems, the high-speed jet generated from the rear engine of an aircraft, flowing nearby the fuselage, can be treated as an offset jet. In this work, an experimental investigation of the interaction noise due to circular high-speed offset jets is performed in an anechoic environment at different nozzle pressure ratios and offset ratios (height of the jet centerline above the plate per nozzle width). A large horizontal plate placed over a height-adjustable stand is used as the offset plate. Acoustic characteristics such as overall sound pressure level and the directivity pattern of free and offset jets are compared for different nozzle pressure ratios. The effect of offset ratio on noise characteristics is also investigated. Flow visualization is also carried out to understand the shock structure and its noise generation mechanism. Acoustic characteristics reveal that noise levels are higher for an offset jet compared to a free jet. Sound pressure levels for offset ratio 0.5 are lower than those for other offset ratios. The noise levels are higher for offset ratio 1.0 due to the presence of feedback tone. Schlieren visualization studies also corroborate the above characteristics.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-03T03:22:09Z
DOI: 10.1177/1475472X221150170
- Acoustic optimization design of porous materials on sandwich panel under
flow-induced vibration-
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Authors: Ye Li, Xinbiao Xiao, Yumei Zhang, Zhao Tang, Aipeng Pan
Abstract: International Journal of Aeroacoustics, Ahead of Print.
In this study, porous sound-absorbing materials used as a lining in double-panel structure applications (such as high-speed train body structures) to limit flow-induced vibration interior noise were studied, and acoustic optimization design was performed. First, in the wavenumber domain, the cross-spectrum Corcos model was used to characterize the dynamic hydrodynamic pressure of turbulence. Biot’s theory is used to model the porous materials. The transmission loss (TL) of the sandwich panel were also determined based on the model superposition method. Three types of sandwich panel structures were considered: air–air (A–A), bonded-bonded (B–B), and bonded-air (B–A). The TL of the three structure types under hydrodynamic pressure was used to evaluate the suppression of flow-induced vibration interior noise in porous materials. The effects of flow velocity, thickness and density of the porous material, and three types of polyimide foam on the TL characteristics of the sandwich panel were investigated. The results show that the flow velocity has a significant influence on the TL of the sandwich panel. The TL of the sandwich panel decreases by 3–4 dB when the flow velocity increases by 100 km/h The B–A configuration has satisfactory sound insulation performance at most frequencies. With an increase in material thickness, the TL of the sandwich panel structure first increases and then decreases, and the material density mainly affects the TL of the structure at intermediate and high frequencies. Based on the objectives of maximizing the average transmission loss (TLavg) and minimizing the structural weight, the acoustic optimization design of the B–A structure was performed, and the balance between the two objective functions was achieved by a nondominated sorting genetic algorithm (NSGA-Ⅱ). The TLavg s of the sandwich panel structure increased by 5.2 dB when the total mass of the structure was decreased by 0.2 kg.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-03T03:12:50Z
DOI: 10.1177/1475472X221150180
- The acoustic performance of a dual Helmholtz resonators system in the
presence of a grazing flow-
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Authors: Rong Xue, Cheuk Ming Mak, Dizi Wu, Kuen Wai Ma
Abstract: International Journal of Aeroacoustics, Ahead of Print.
Helmholtz resonators (HR) are widely used in aero-engine systems for noise reduction. By connecting a pair of HRs in series (neck-cavity-neck-cavity), a dual HRs system is formed. This study investigated the influence of neck length, cavity volume and flow Mach number on the noise attenuation performance of a dual HRs system. A three-dimensional numerical simulation was performed to calculate the transmission loss results. The transmission loss (TL) results indicated that the second neck length can influence the second resonance frequency and TLmax. Changing the cavity volume significantly influences the noise attenuation ability under lower flow rate conditions compared to higher flow rate conditions. The flow Mach number had a more significant impact on the first TL peak than on the second TL peak. This study shows the relationship between the geometric parameters, grazing flow and noise attenuation performance of a dual HRs system and could provide guidance in designing suitable dual HRs for aero-engine systems.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-02T03:57:28Z
DOI: 10.1177/1475472X221150175
- Hydrodynamic sources of the vortex sound in a two-dimensional shear layer
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Authors: Yongle Du, Hangwen Yu, Yanchen Liu, Dangguo Yang
Abstract: International Journal of Aeroacoustics, Ahead of Print.
Development of advanced noise reduction devices requires an in-depth understanding of two fundamental questions: what are the true noise sources and how are the acoustic radiations generated. An accurate separation of the hydrodynamic and acoustic fluctuations helps to reveal the answers, but no consensus exists on its feasibility in the near-field source region of compressible flows. This study proposes a methodology to examine the dynamics of vortex sound generation in a two-dimensional artificially excited subsonic mixing layer. The parabolized stability equation (PSE) is applied to resolve the hydrodynamic fluctuations and the vortex sound theory is used to predict the acoustic pressures. Numerical simulations show that the PSE solutions capture the vortex pairing reasonably accurately and damp the acoustic modes to a negligible level, and that the vortex sound theory recovers the acoustic pressures. Good agreement of both solutions with the direct simulations indicates that a physically reasonable separation of hydrodynamic sources is achieved and can be used to further examine the vortex dynamics and noise source mechanisms.
Citation: International Journal of Aeroacoustics
PubDate: 2023-01-02T03:45:39Z
DOI: 10.1177/1475472X221150177
- Guest editor biography
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Pages: 657 - 657
Abstract: International Journal of Aeroacoustics, Volume 21, Issue 8, Page 657-657, November 2022.
Citation: International Journal of Aeroacoustics
PubDate: 2022-12-07T02:39:39Z
DOI: 10.1177/1475472X221141788
Issue No: Vol. 21, No. 8 (2022)
- Experimental investigation of the laminar boundary layer vortex-shedding
noise by an airfoil within a closed-vein wind tunnel-
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Authors: Stéphane Redonnet, Thomas G Schmidt
Pages: 658 - 683
Abstract: International Journal of Aeroacoustics, Volume 21, Issue 8, Page 658-683, November 2022.
This study concerns the experimental characterization of trailing edge noise, the understanding of which is crucial for mitigating acoustic pollution across major industries. An aeroacoustic experiment is carried out using a closed-vein wind tunnel to investigate the laminar boundary layer vortex-shedding (LBL-VS) noise of a symmetric NACA0021 airfoil in low Reynolds number flows (Re ≤ 163,500). Steady aerodynamic and acoustic measurements are performed, with numerous conditions covered (flow velocity from 10 m/s to 24.5 m/s, airfoil incidence from −10° to 10°). The aerodynamic results reveal that, in the pre-stall regime, the airfoil’ suction side exhibits both a laminar separation bubble (LSB) and a trailing edge detached flow – which both make LBL-VS noise likely to occur. The acoustic results reveal that, when at low speed and moderate incidence, the airfoil emits one to two tones, which can be both attributed to LBL-VS noise. In particular, their respective frequency is seen to scale as the 0.8th power of the flow velocity, whereas varying linearly with the incidence. At higher speeds, these two tones vanish to the profit of other, more intense tonal emissions, whose frequency does not scale with the velocity nor the incidence. These tones are attributed to resonance effects coming from a retroaction of the reverberant environment onto the LBL-VS noise emission, which then locks-on to some of the duct resonant frequencies via an acoustic feedback loop. Revealing indirectly the presence of the pre-existing LBL-VS noise, these resonant tones emerge only when the flow velocity and incidence obey specific conditions, namely a roughly linear relationship.
Citation: International Journal of Aeroacoustics
PubDate: 2022-12-07T02:39:38Z
DOI: 10.1177/1475472X221136882
Issue No: Vol. 21, No. 8 (2022)
- Jet noise sources for chevron nozzles in under-expanded condition
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Authors: Hasan Kamliya Jawahar, Stefano Meloni, Roberto Camussi
Abstract: International Journal of Aeroacoustics, Ahead of Print.
Imperfectly expanded jet flows are known to have additional noise sources known as Screech and broadband shock-associated noise. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock cell structures. In this study, thorough experimental investigations were carried out on chevron nozzles to assess the importance of chevron parameters such as the chevron count and chevron penetration angle on the pressure field emitted by the jet. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as pressure spectra, directivity and overall sound pressure levels along with near-field measurements were acquired for jet Mach numbers ranging from M = 1.1–1.4. Fourier-based and Wavelet-based analyses were used to highlight the different features of the various tested nozzles. Wavelet decomposition results highlight that the presence of the chevrons reduce the acoustic noise especially at a higher axial distance with increased levels of noise reduction achieved by chevron nozzle with deep penetration angle.
Citation: International Journal of Aeroacoustics
PubDate: 2022-06-21T06:18:18Z
DOI: 10.1177/1475472X221101766
- Corrigendum to The effect of the convective momentum transfer on the
acoustic boundary condition of perforated liners with grazing mean flow-
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Abstract: International Journal of Aeroacoustics, Ahead of Print.
Citation: International Journal of Aeroacoustics
PubDate: 2022-04-12T03:00:03Z
DOI: 10.1177/1475472X221096743
- Data-driven neural networks for source localization and reconstruction
using a planar array-
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Authors: Sai Manikanta Kaja, Srinath Srinivasan, S. K. Chaitanya, K. Srinivasan
First page: 684
Abstract: International Journal of Aeroacoustics, Ahead of Print.
This study uses specialized deep neural networks comprising dense and convolutional neural networks to localize noise sources and reconstruct acoustic data on a reconstruction plane. The networks are trained on simulated acoustic data free from any form of noise in the signal. It is observed that neural networks can effectively localize monopole and dipole sources and reconstruct the acoustic data in reconstruction planes with higher accuracy than conventional methods. Performance of the networks is consistent over changes in some parameters like the source strength, noise in the input signal, and frequency range. Various tests are performed to assess the individual network performance. Results indicate that neural networks trained on a subset of the data are effective over the entire data set without significant bias or variance. Errors as low as 1% are observed, and the maximum error observed is below 5%. While reconstruction error decreased with an increase in the frequency of monopole sources, it increased with an increase in frequency for dipole sources.
Citation: International Journal of Aeroacoustics
PubDate: 2022-11-11T12:29:22Z
DOI: 10.1177/1475472X221136884
- Reduction of noise generated by cylinder-airfoil interaction using grooved
structures on the upstream cylinder-
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Authors: Chengchun Zhang, Xiaowei Sun, Tianyu Du, Chun Shen, Zhengwu Chen, Dong Liang, Jiale Zhao, Yingchao Zhang
First page: 708
Abstract: International Journal of Aeroacoustics, Ahead of Print.
The cylinder-airfoil interaction noise can be reduced by changing the shape of the leading edge of the downstream airfoil. Generally, this way not only can reduce the interaction noise at middle and high frequency, but also can change the peak noise at the low frequency. This study attempts to affect the cylinder-airfoil interaction noise from the perspective of reducing the intensity of the upstream wake shedding vortex. In order to achieve this target, the equally spaced grooves were cut into the upstream cylinder, and the acoustic wind tunnel tests at various incoming velocities (20–60m·s−1) were conducted to compare the interaction noise of cylinder-airfoil (NACA0012) models. It is found that the grooved structure can effectively reduce the peak noise at characteristic frequencies bellow 1000 Hz and the broadband noise in the mid-frequency ranging from 1000 Hz to 3000 Hz, especially for the higher incoming velocity. Thereinto, the peak noise and overall sound pressure level (OASPL) with the grooved cylinder are reduced by 13 dB and 7.2 dB, respectively at the incoming velocity of 60 m·s−1. The numerical simulations based on the large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) acoustic analogy were performed to further reveal the mechanisms of noise reduction when the velocity is 60 m·s−1. The results show that the vortex shedding from cylinder wake is suppressed by the grooved cylinder and the vortex structure at the leading edge of the airfoil is also cut into the small-scale vortex structures by the grooved structure. The pressure fluctuation amplitude and the peak value turbulent kinetic energy in the wake of the grooved cylinder are significantly reduced. In addition, the further spectrum analysis reveals that the weak correlation of the vortex shedding on the grooved cylinder could lead to the suppression of the pressure fluctuation in the cylinder wake, and thereby the interaction noise is significantly reduced.
Citation: International Journal of Aeroacoustics
PubDate: 2022-10-29T02:15:16Z
DOI: 10.1177/1475472X221136885
- Numerical study on the noise propagation characteristics of rotor in
non-uniform downwash flowfield Based on Linearized Euler Equations-
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Authors: Tao Yang, Xi Chen, Qijun Zhao, Guoqing Zhao
First page: 731
Abstract: International Journal of Aeroacoustics, Ahead of Print.
To study the influence of non-uniform flowfield on the propagation characteristics of helicopter rotor noise, a Hybrid Computational Aeroacoustics (HCAA) method is developed. The acoustic source region is simulated by Computational Fluid Dynamics (CFD) technique with the Unsteady Reynolds Averaged Navier-Stokes equations (URANS) as the governing equations. Acoustic near-field is simulated by Computational Aeroacoustics (CAA) technique with the Linearized Euler Equations (LEE) as the governing equations, and the numerical discretization of the LEE is accomplished by Runge-Kutta Discontinuous Galerkin (RKDG) method. A novel acoustic source extraction method based on pressure and pressure gradient is proposed to accomplish the one-way CFD-CAA weak coupling. The HCAA method is validated through comparisons with noise experimental data of the UH-1H model rotor and the BO-105 model rotor. Based on the proposed HCAA method, the convection and refraction effects of rotor noise under different collective pitch angles are analyzed. The results show that the distortion effect of the rotor noise is most affected by the non-uniformly distributed downwash velocity field, resulting in an increment of acoustic energy below the rotor plane. The effect of non-uniformly distributed downwash velocity on noise propagation increases with the increase of the collective pitch angle. For the UH-1H model rotor, the maximum change of the sound pressure level is 0.8 dB (about 10% change of the effective sound pressure).
Citation: International Journal of Aeroacoustics
PubDate: 2022-11-09T09:46:59Z
DOI: 10.1177/1475472X221136883
- Aerodynamic noise characteristics of non-circular cylinders in subcritical
flow regime-
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Authors: Arun MG, Sarvoththama Jothi TJ
First page: 766
Abstract: International Journal of Aeroacoustics, Ahead of Print.
The present study experimentally investigates the aerodynamic noise from the flow around cylinders of square and equilateral triangle cross-sections at different angles of incidence (α). The cylinder models have a side dimension of 10 mm and a span of 300 mm. The free stream velocity (U0) is in the range of 12–36 m/s, and the corresponding Reynolds numbers are 7.8 × 103 to 2.3 × 104, which is in the subcritical flow regime. The characteristic acoustic tones are generated at α = 30° and 45° for square and triangular cylinders. The frequency of acoustic tones linearly increases with the free stream velocity, and the corresponding Strouhal numbers are found to be in the range of 0.13–0.16. Depending on the angle of incidence, the overall sound pressure level is higher than the background noise by 4–24 dB for the square cylinder and 3–15 dB for the triangular cylinder at U0 = 36 m/s. The highest noise level of the square cylinder is 90 dB at α = 45° and 79 dB at α = 30° for the triangular cylinder. The spectral scaling with the sixth power of the free stream velocity indicates the dipole behaviour of the acoustic tones. The mean and root-mean-square velocity profiles in the wake region characterise the noise emissions at different angles of incidence. The comparative acoustic study of the non-circular cylinders with a circular counterpart showed that the highest noise level is from the square cylinder at α = 45°. The directivity study shows that the noise level of the square cylinder at α = 45° at 90° angular location (θ) is higher by 6.5 dB than that at θ = 30°.
Citation: International Journal of Aeroacoustics
PubDate: 2022-11-15T05:35:57Z
DOI: 10.1177/1475472X221140869
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Hybrid journal (It can contain Open Access articles)
