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Pages: 97 - 97 Abstract: International Journal of Aeroacoustics, Volume 21, Issue 3-4, Page 97-97, June 2022.
Citation: International Journal of Aeroacoustics PubDate: 2022-05-30T07:24:50Z DOI: 10.1177/1475472X211061783 Issue No:Vol. 21, No. 3-4 (2022)
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Authors:Chitrarth Prasad, Scott Hromisin, Philip J Morris Abstract: International Journal of Aeroacoustics, Ahead of Print. Noise source imaging based on phased array measurements is an essential tool in the aeroacoustic analysis of new nozzle designs, especially at full-scale. This investigation aims to assess the capability of a deconvolution-based beamforming technique to accurately estimate the changes in noise sources for model-scale heated military jets when fluid inserts are used for noise control. This goal is achieved by performing well-validated Large Eddy Simulations (LES) to complement the experimental measurements. The LES data is segregated into its hydrodynamic, acoustic and thermal components using Doak’s Momentum Potential Theory (MPT). The near-field MPT-derived components are subjected to Spectral Proper Orthogonal Decomposition (SPOD) to compare with the frequency-dependent noise source maps obtained directly from experiments. It is shown that fluid inserts alter the naturally occurring Kelvin-Helmholtz (K-H) instability in the jet shear layer, which leads to a change in the directivity of the noise radiated in the near-field. The upstream shift in the noise source distribution resulting from the modified K-H instability is accurately captured by the deconvolution-based source imaging technique using just the far-field measurements. These changes in source locations as a function of frequency are documented. Citation: International Journal of Aeroacoustics PubDate: 2022-06-23T07:10:05Z DOI: 10.1177/1475472X221107359
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Authors:Dong Yang, Juan Guzmán-Iñigo, Aimee S. Morgans Abstract: International Journal of Aeroacoustics, Ahead of Print. For a single-component perfect gas, entropy perturbations are associated with the difference between the overall density fluctuation and that coming from the acoustic perturbation. Entropy perturbations can generate sound when accelerated/decelerated by a non-uniform flow and this is highly relevant to thermoacoustic instabilities for gas turbines and rocket engines, and to noise emission for aero-engines. Widely used theories to model this entropy-generated sound rely on quasi-1D assumptions for which questions of validity were raised recently from both numerical and experimental studies. In the present work, we build upon an acoustic analogy theory for this problem. This theory was initiated by Morfey (J. Sound Vib. 1973) and Ffowcs Williams and Howe (J. Fluid Mech. 1975) about 50 years ago and extended recently by Yang, Guzmán-Iñigo and Morgans (J. Fluid Mech. 2020) to study the effect of non-plane entropy waves at the inlet of a flow contraction on its sound generation. Comparisons against both numerical simulations and previous theory are performed to validate the results. Citation: International Journal of Aeroacoustics PubDate: 2022-06-23T01:34:09Z DOI: 10.1177/1475472X221107368
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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
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Authors:Aharon Z Karon, Krishan K Ahuja Abstract: International Journal of Aeroacoustics, Ahead of Print. Often the measurements from different jet noise studies, which are thought to have been acquired at or corrected to identical jet conditions, do not match when compared to each other. This study looks at the nozzle-exit boundary layer as a possible factor for these differences. The nozzle-exit boundary layer state can easily be changed depending on the design of the jet-facility or the nozzle. To this end, jet noise measurements and nozzle-exit velocity profile measurements were acquired for nozzles where the nozzle-exit boundary state was changed either by using different types of nozzles, ASME nozzles versus conical nozzles, or extensions were added to the nozzles straight section. It is shown that as the laminar boundary layer transitions to turbulent, the high-frequency jet noise is reduced. In addition, development of a novel empirical correction for these effects was attempted. Citation: International Journal of Aeroacoustics PubDate: 2022-06-15T01:45:43Z DOI: 10.1177/1475472X221107375
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Authors:Ann P Dowling Abstract: International Journal of Aeroacoustics, Ahead of Print. I first met Shôn in October 1973. I had just started Part III of the Cambridge Mathematical Tripos – a post-graduate course that was retrospectively awarded a Masters’ Degree in Mathematics. After a summer job working with Ted Broadbent on aircraft noise at the Royal Aircraft Establishment in Farnborough, I had decided do a PhD in Aeroacoustics. I asked Sir James Lighthill for advice and he told me that he was now focused on biomechanics but a new professor had recently arrived in the Cambridge Department of Engineering and that I should ask him. I made contact with Shôn, saw him in his office that afternoon, and he agreed to supervise me for a PhD. As quickly and simply as that, I was on a path that for me was transformational, not only an exciting research future, but the start of my transition from mathematics into engineering. Throughout my career, Shôn continued to be a major influence on me as he has for many others. Citation: International Journal of Aeroacoustics PubDate: 2022-06-13T05:12:24Z DOI: 10.1177/1475472X221107356
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Authors:Alexander Karakulev, Tatiana Kozubskaya, Gleb Plaksin, Ivan Sofronov Abstract: International Journal of Aeroacoustics, Ahead of Print. The paper expands the scope of applying the Ffowcs Williams – Hawkings integration method. We propose using the acoustic field generated from time-dependent data stored on the FW-H control surface as the same common field for computational acoustic beamforming and dynamic mode decomposition methods to analyze the aerodynamic noise sources. We exemplify that it leads to obtaining mutually consistent and complementary information for reliable prediction of acoustic sources characteristics in the process of inverting data produced by a CFD simulation. Moreover, as the results of applying computational acoustic beamforming and dynamic mode decomposition methods depend on many geometric and algorithmic inputs, the proposed approach makes it possible to use various sets of the latter for a comprehensive analysis of obtained inversions and to form the final answer by an averaging procedure. We illustrate this by taking advantage of fast generating the examined acoustic field snapshots in any required region by the FW-H integration method for the recently developed new inverse computational acoustic beamforming algorithm and the standard dynamic mode decomposition method when carrying out a sensitivity study of the predicted acoustic source. The capabilities of the developed approach are demonstrated on the data of CFD scale-resolving simulation of turbulent flow over the 30P30N high-lift configuration. Citation: International Journal of Aeroacoustics PubDate: 2022-06-12T07:46:43Z DOI: 10.1177/1475472X221107367
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Authors:Anjaneyulu Krothapalli Abstract: International Journal of Aeroacoustics, Ahead of Print.
Citation: International Journal of Aeroacoustics PubDate: 2022-06-12T06:42:44Z DOI: 10.1177/1475472X221107373
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Authors:Christopher R Fuller Abstract: International Journal of Aeroacoustics, Ahead of Print. IReduction of fan noise is an important problem in the successful deployment of drones and UAV's. This paper considers a new approach to reducing fan and propeller noise based upon micro vibrations of the propeller blades around their axis of support. Experimental testing was carried out on a five bladed fan arrangement. The micro fan blade vibrations are induced with a pitch link actuator arrangement driven by an electromagnetic actuator. When used in conjunction with a digital feedforward active noise controller, the micro blade vibrations were found to provide global attenuations of fan radiated sound the order of 5 to 10dB of the first few fan tones. The level of required vibrations and the associated electrical power required for the cancelling micro vibrations was shown to be very small compared to the fan motor power requirements. The results demonstrate that the innovative approach, termed “self active cancellation of fan noise”, has good potential for global reduction of fan and propeller noise. Citation: International Journal of Aeroacoustics PubDate: 2022-06-10T11:20:38Z DOI: 10.1177/1475472X221107543
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Authors:Russell H Thomas, Yueping Guo Abstract: International Journal of Aeroacoustics, Ahead of Print. Based on classical diffraction theories with modifications and extensions in analytical formulations and numerical implementations, a new code has been developed at NASA for the prediction of aircraft noise shielding, named as Propulsion Airframe Aeroacoustic Shielding Attenuation (PAAShA). The code is developed primarily for aircraft system noise predictions, although it may also be useable in other applications with acoustic shielding. The requirements for this code are driven by the need for a robust, capable code to use with NASA’s Aircraft Noise Prediction Program (ANOPP) for aircraft integration and system noise research. The requirements are met and include capabilities to use a wide range of aircraft geometries, rapid calculation times consistent with aircraft system noise problems, and the flexibility to model realistic noise source characteristics and distributions. The accuracy and robustness of the method are demonstrated in this paper with a set of problems, including a cylinder, a finite plate, a symmetrical two-dimensional airfoil, and a full three-dimensional hybrid wing body aircraft model tested in a wind tunnel. This range of problems demonstrates both smooth and sharp edge diffraction capabilities for a wide range of frequencies and low Mach number flow effects at low angles of attack. Predictions are shown to be accurate to within 1–4 dB over a wide range of the most significant frequencies and directivity angles. This is determined by comparing with data, which have experimental uncertainties, particularly at high frequencies, high angles, and source characteristics. The accuracy diminishes for geometries that include a significant reflection component, which is not calculated by the code. Accuracy can also be somewhat diminished for high azimuthal angles. Accurate modeling of the noise source, particularly its frequency and directivity characteristics, is essential to obtaining accurate results. Citation: International Journal of Aeroacoustics PubDate: 2022-06-10T02:03:01Z DOI: 10.1177/1475472X221107369
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Authors:Nick P Breen, Krish K Ahuja Abstract: International Journal of Aeroacoustics, Ahead of Print. Over the years, there have been numerous studies on determining subsonic jet noise source locations, typically plotted as Strouhal number as a function of distance from the nozzle exit. A comparison of the results of various studies yields a spread of about two nozzle diameters in measured source location. This work examines how boundary layer thickness, which can vary from nozzle to nozzle, could be the cause of observed differences in different studies in subsonic jet noise source location. Source location measurements of unheated jets from ASME nozzles, which have comparably thinner nozzle exit boundary layers, and conical nozzles, which have comparably thicker nozzle exit boundary layers, are compared. These results are substantiated with the use of schlieren flow visualization and velocity profile measurements. It is found that the nozzles with thinner nozzle exit boundary layers have noise source distributions that are 0.25–2 diameters upstream of those with thicker nozzle exit boundary layers. Thinner nozzle exit boundary layers result in higher growth rates of instability waves, increasing mixing and thereby moving noise sources upstream. Citation: International Journal of Aeroacoustics PubDate: 2022-06-08T01:01:32Z DOI: 10.1177/1475472X221107370
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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
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Authors:C Yang, LL Sun, H Guo, YS Wang, Y Shao First page: 98 Abstract: International Journal of Aeroacoustics, Ahead of Print. To improve the computation and real-time performances of the multiple signal classification (MUSIC) algorithm in 3D space, a fast sound source localization method based on the bat algorithm (BA) and the 3D-MUSIC, called BA-based 3D-MUSIC algorithm (3D-BMUSIC), is presented in this paper. 3D-BMUSIC greatly reduces the computation load by replacing the regular grid search with the BA. First, the near-field spherical wave model is established to obtain the spectral function of the 3D-MUSIC. Then, the spectral function is defined as the fitness function, which calculates the fitness value corresponding to each bat position. Finally, the global optimal bat position with the largest fitness value, as sound source localization, is obtained by successive iteration and sorting. The simulation and experiment show that 3D-BMUSIC accurately estimates the DOA and distance of near-field sources, and the root-mean-square error (RMSE) of 3D-BMUSIC is less than that of 3D-MUSIC. In addition, 3D-BMUSIC effectively reduces the computation time by approximately 96–98%. With shorter computation time and higher efficiency, 3D-BMUSIC promotes hardware implementation and is more suitable for high-precision localization of near-field sound sources. Citation: International Journal of Aeroacoustics PubDate: 2022-04-22T01:04:38Z DOI: 10.1177/1475472X221093711
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Authors:Hyunshik Joo, Taeyoung Park, Seung-Hoon Kang, Sangjoon Shin, Won-Suk Ohm First page: 115 Abstract: International Journal of Aeroacoustics, Ahead of Print. The goal of this paper is to examine the computational approaches for predicting both of the overall sound pressure level (OASPL) at a few locations and acceleration power spectral density (APSD) of surrounding thin plates due to the aero-acoustic pressure generated by a cold jet with M = 1.8. First, computational fluid dynamics (CFD), particularly delayed detached eddy simulation, are applied to predict the OASPL at the near-field and compute the acoustic properties. Second, the linearized boundary element method (BEM), that is, the Helmholtz-Kirchhoff method is utilized to propagate the pressure and obtain the OASPL at the far-field. Finally, the finite element method is implemented to predict the APSD for a clamped thin plate based on the optimal triangle membrane element, discrete Kirchhoff triangle plate bending element, and Newmark-β time integration scheme. Using the present CFD and BEM, the OASPLs are compared with the experimental results measured by microphones at both the near- and far-fields, respectively. Moreover, APSDs are compared with the experimental results obtained by an accelerometer at a few different locations. Although OASPLs are overestimated because of the coarse meshes in the higher-angle area and low order scheme of the present CFD analysis, the present integrated aero-vibro-acoustic analysis is capable of predicting the OASPL and APSD generated by a cold jet with M = 1.8. Citation: International Journal of Aeroacoustics PubDate: 2022-05-12T12:46:23Z DOI: 10.1177/1475472X221093702
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Authors:Joemon Jacob, Subrata Kumar Bhattacharya First page: 142 Abstract: International Journal of Aeroacoustics, Ahead of Print. Flow-induced aerodynamic noise from four cylindrical shapes of infinite length at a low subcritical flow regime is studied using Large Eddy Simulation (LES) and acoustic analogy. Numerical simulations are performed for short-span (length to diameter ratio of 3) cylinders, and a sound correction method based on equivalent/spatial coherence length has been applied to estimate noise from long-span cylinders. An attempt is made to compare spatial coherence lengths of four cross-sections at the same Reynolds number (Re). The sound correction method that is well established for circular cylinders proved effective for non-circular cross-sections also. Owing to the limitation in computational capacity, a well-resolved LES is still unachievable for higher Re flows and long-span cylinders without adopting a sound correction methodology. A grid resolution based on the characteristic length and velocity scale was adopted in simulation and proved effective for computing aerodynamic and aeroacoustic characteristics. An ‘effective frequency band’ of sound pressure level-frequency curve is proposed that predicts over 99.5% of the overall sound pressure level, and features of this band for four cross-sections are presented. Citation: International Journal of Aeroacoustics PubDate: 2022-04-23T08:54:51Z DOI: 10.1177/1475472X221093713
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Authors:Penglin Zhang, Cheng Yang, Yu Huang First page: 168 Abstract: International Journal of Aeroacoustics, Ahead of Print. The impedance eduction technique is widely used by the aeroacoustics community to obtain liner property in a flow duct. However, the obtained impedance is often found to be discontinuous in the frequency domain which violates theoretical liner models. The low signal-to-noise ratio (SNR, in dB) is one factor leading to this unexpected result. To overcome this, a weighting coefficient, represented by an SNR dependent sigmoid function with two control parameters, is introduced to the cost function in the iteration process. The proposed algorithm is employed to measure the impedances of two liners and results show an improvement in the smoothness of the resultant impedance curves over those obtained from conventional cost function. Citation: International Journal of Aeroacoustics PubDate: 2022-04-21T04:05:06Z DOI: 10.1177/1475472X221093710
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Authors:Sang Hyun Kim, Tae Seon Park First page: 190 Abstract: International Journal of Aeroacoustics, Ahead of Print. To correct the balance of the rotating assembly of a turbocharger, some parts of the compressor wheel are removed by cutting. A numerical investigation of the turbulent flows and flow noises produced by compressor wheels modified with such cutting parts was performed by a turbulence model and detached-eddy simulations. For the 6-cutting case, 0, 2, 4, and 6 circular cuttings and two additional—rectangular and triangular—shapes were used.To investigate the effects of the balance cuttings in a compressor wheel, the evaluation process using computational fluid dynamics was tried. It was found that the fluid forces due to the various wheel shapes have the potential to restore the eccentricity by approximately 50%. Severe variations of velocity, pressure, and turbulent kinetic energy in the interspace between the wheel and volute were observed. In particular, the wavelike patterns of pressure and turbulent kinetic energy were intensified for the modified wheels. The turbulent kinetic energy of the 6-cutting case had a dominant frequency at approximately 3000 Hz. The spectrum of the sound-pressure level of the modified compressor wheels exhibited the features of buzz-saw noise. The flow fields suggested that this feature of the sound pressure is related to the tip-clearance flow affected by the balance cuttings. In addition, the acoustic pressure and flow characteristics of the different types of modified compressor wheels were discussed and the resulting acoustic power was evaluated. Citation: International Journal of Aeroacoustics PubDate: 2022-04-22T11:00:21Z DOI: 10.1177/1475472X221093707
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Authors:Chaowei Li, Jianyue Zhu, Zhiwei Hu, Zhenyu Lei, Yingmou Zhu First page: 218 Abstract: International Journal of Aeroacoustics, Ahead of Print. The aerodynamic noise behavior of flow passing the simplified leading car and nose car scale models of a high-speed train is investigated through the vortex sound theory and acoustic analogy approach. The unsteady flow developed around the geometries is solved numerically and the data are applied to study the near-field quadrupole sound source and calculate the far-field noise radiated. It is found that the turbulent flow developed around the leading car is characterized by multi-scale vortices separated from the geometries. The intensity of volume dipole source is much larger than that of volume quadrupole source and the volume dipole source becomes the predominate source of the near-field quadrupole noise. The flow is separated noticeably in the regions of the nose, bogies, bogie cavities, and train tail of the leading car where the pressure fluctuations are generated largely upon the solid surfaces and correspondingly a dipole noise of high level is produced. By comparison, the noise contribution from the leading bogie and bogie cavity is larger than that from the other components. Moreover, the numerical and experimental results of train nose car model demonstrate that the flow around the bogie region is the dominant aerodynamic sound source. Therefore, the flow-induced noise generated from the leading cars may be reduced efficiently within a certain frequency range and specific direction by mitigating the flow interactions around the areas of leading bogie and bogie cavity. Citation: International Journal of Aeroacoustics PubDate: 2022-05-18T06:17:36Z DOI: 10.1177/1475472X221093701
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Authors:Lukas Klähn, Antoine Moreau, Luciano Caldas, Robert Jaron, Ulf Tapken First page: 239 Abstract: International Journal of Aeroacoustics, Ahead of Print. With the objective to improve the understanding of the dominant fan noise source mechanisms, a comprehensive experimental study was conducted at a low speed fan test rig. The aerodynamic fan map as well as the acoustic characteristics of the fan was measured for a new blade integrated disk (Blisk) rotor with systematic variation of the shaft speed and throttling. The interpretation of the results is supported by simulations of the experiment with a physics-based analytical in-house tool for fan noise prediction. For the acoustic measurements, an array of wall-flushed microphones was used in the inlet section. By means of radial mode analysis techniques, the broadband and tonal sound powers are calculated for each operating point. In the obtained comprehensive database, systematic variations of the tonal and broadband sound power with the flow rate are found. These patterns can only partly be correlated to the varying incidence angle of the rotor blades. Comparing the mode distributions of the measured noise and the analytical models then allows conclusions on the predominant noise sources of rotor–stator interaction and inflow-rotor interaction. Citation: International Journal of Aeroacoustics PubDate: 2022-04-26T01:17:00Z DOI: 10.1177/1475472X221093703
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Authors:Hyunjune Gill, Seongkyu Lee First page: 260 Abstract: International Journal of Aeroacoustics, Ahead of Print. Trailing-edge noise is known to be sensitive to airfoil shapes, and ice accretion is one cause of an airfoil shape deformation. This paper investigates how trailing-edge noise is affected by the airfoil shape deformation due to ice accretion. The formation of ice-induced flow separation and the development of a turbulent boundary layer are analyzed to understand the correlation between the altered flow physics due to ice accretion inside the boundary layer and trailing-edge noise. The near-wall flow behind the leading-edge ice accretion is analyzed by using Reynolds-Averaged Navier Stokes CFD in OpenFOAM, and trailing-edge noise is investigated using an empirical wall pressure spectrum model in conjunction with Amiet’s trailing-edge noise theory. Validations of tools against measurement data are presented. Liquid water content, freestream velocity, and ambient temperature are varied to investigate the impact of flow conditions on the ice accretion shape and the resulting boundary layer flow characteristics at the trailing edge. It is found that a more significant leading edge deformation due to ice accretion generates larger ice-induced flow separation bubbles, which increases the trailing-edge boundary layer thickness. As a result, an increase in low- and mid-frequency noise is observed. The purpose of this paper is not only to understand the effect of ice accretion on trailing-edge noise but also to comprehensively analyze how flow physics inside the turbulent boundary layer is altered by the presence of various ice accretion shapes. Citation: International Journal of Aeroacoustics PubDate: 2022-05-14T12:39:25Z DOI: 10.1177/1475472X221099497
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