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1
Testa, C., S. Ianniello, F. Salvatore, and M. Gennaretti. "Numerical Approaches for Hydroacoustic Analysis of Marine Propellers." Journal of Ship Research 52, no. 01 (March 1, 2008): 57–70. http://dx.doi.org/10.5957/jsr.2008.52.1.57.
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This paper is devoted to a theoretical and numerical hydroacoustic analysis of marine propellers. The use of the Ffowcs Williams-Hawkings equation is addressed and compared with a Bernoulli-based methodology, typically used in the naval context. A computational tool based on a boundary element formulation for the velocity potential is used to determine the hydrodynamic loads on the propeller blades. Then, both the Bernoulli and the Ffowcs Williams-Hawkings equations are used to evaluate the pressure far field. The role played by the incompressibility assumption is treated from theoretical and computational points of view; thus, some other numerical issues, concerning the wake modeling effects and the alternative methodologies, are discussed in order to assess the superiority of the acoustic analogy approach and to support its use for naval applications.
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Casalino, Damiano, Marc Jacob, and Michel Roger. "Prediction of Rod-Airfoil Interaction Noise Using the Ffowcs-Williams-Hawkings Analogy." AIAA Journal 41, no. 2 (February 2003): 182–91. http://dx.doi.org/10.2514/2.1959.
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Dunn, Mark H. "The acoustic analogy in four dimensions." International Journal of Aeroacoustics 18, no. 8 (November 2019): 711–51. http://dx.doi.org/10.1177/1475472x19890259.
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The classical acoustic analogy theory is incomplete in the sense that the original research on the subject focused only on the prediction of acoustic pressure. There were no provisions for predicting the three components of acoustic velocity which are needed as input for aeroacoustic scattering applications. This is because the scalar wave equations of Lighthill and Ffowcs Williams and Hawkings were derived from the fluid conservation equations by eliminating three of the four governing differential equations from which the acoustic velocity could have been obtained. Recently developed acoustic analogy methods for predicting the acoustic velocity lead to complex formulations whose numerical evaluation can be problematic when providing input for large-scale scattering problems. Their calculation can overwhelm the numerical scattering process when the incident sound has high-frequency content, such as that produced by the rotating blades of various propulsion devices. To obtain improved acoustic analogy formulations for scattering and other applications, the three discarded differential equations are returned to the analysis in this paper and the historical acoustic analogy equations are derived anew using four-dimensional tensor methods. The 4-D formulation is an application of the electromagnetic analogy (EMA), a concept based on the equivalence of Maxwell’s equations and the fluid conservation equations of mass and momentum. The scalar equations of Lighthill, Ffowcs Williams and Hawkings, Farassat, and Kirchhoff are extended to four equations – one equation for the acoustic pressure (or acoustic density) and three equations for the acoustic velocity. The 4-D tensor representation provides significant theoretical and computational simplification relative to the classical approach. For each of the original acoustic analogy results, a single, concise formulation in 4D is derived that enables the simultaneous prediction of acoustic pressure and the three components of acoustic velocity.
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Lidtke, Artur K., Stephen R. Turnock, and Victor F. Humphrey. "Characterisation of sheet cavity noise of a hydrofoil using the Ffowcs Williams–Hawkings acoustic analogy." Computers & Fluids 130 (May 2016): 8–23. http://dx.doi.org/10.1016/j.compfluid.2016.02.014.
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Schoder, Stefan, Clemens Junger, and Manfred Kaltenbacher. "Computational aeroacoustics of the EAA benchmark case of an axial fan." Acta Acustica 4, no. 5 (2020): 22. http://dx.doi.org/10.1051/aacus/2020021.
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This contribution benchmarks the aeroacoustic workflow of the perturbed convective wave equation and the Ffowcs Williams and Hawkings analogy in Farassat’s 1A version for a low-pressure axial fan. Thereby, we focus on the turbulence modeling of the flow simulation and mesh convergence concerning the complete aeroacoustic workflow. During the validation, good agreement has been found with the efficiency, the wall pressure sensor signals, and the mean velocity profiles in the duct. The analysis of the source term structures shows a strong correlation to the sound pressure spectrum. Finally, both acoustic sound propagation models are compared to the measured sound field data.
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Epikhin, Andrey, Matvey Kraposhin, and Kirill Vatutin. "The numerical simulation of compressible jet at low Reynolds number using OpenFOAM." E3S Web of Conferences 128 (2019): 10008. http://dx.doi.org/10.1051/e3sconf/201912810008.
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The paper presents an analysis of various approaches for calculation gas-dynamic parameters and acoustic perturbations generated by a compressible jet at low Reynolds number (M = 0.9, Re = 3600). The jet flow parameters at selected conditions are well studied and can be used for validation of the numerical methods and schemes. The OpenFOAM software package with various approaches (solvers) such as pimpleCentralFoam, dbnsTurbFoam and new QGDFoam solver based on QGD-algorithms are considered. The results of time-averaged flow parameters and acoustic properties are compared with the experimental data. To determine the acoustic perturbation the Ffowcs Williams and Hawkings analogy implemented in our OpenFOAM library (libAcoustic) has been used.
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Najafi-Yazdi, Alireza, Guillaume A. Brès, and Luc Mongeau. "An acoustic analogy formulation for moving sources in uniformly moving media." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, no. 2125 (June 30, 2010): 144–65. http://dx.doi.org/10.1098/rspa.2010.0172.
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Acoustic analogy methods are used as post-processing tools to predict aerodynamically generated sound from numerical solutions of unsteady flow. The Ffowcs Williams–Hawkings (FW–H) equation and related formulations, such as Farassat’s Formulations 1 and 1A, are among the commonly used analogies because of their relative low computation cost and their robustness. These formulations assume the propagation of sound waves in a medium at rest. The present paper describes a surface integral formulation based on the convective wave equation, which takes into account the presence of a mean flow. The formulation was derived to be easy to implement as a numerical post-processing tool for computational fluid dynamics codes. The new formulation constitutes one possible extension of Farassat’s Formulation 1 and 1A based on the convective form of the FW–H equation.
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Schoder, Stefan, and Manfred Kaltenbacher. "Hybrid Aeroacoustic Computations: State of Art and New Achievements." Journal of Theoretical and Computational Acoustics 27, no. 04 (December 2019): 1950020. http://dx.doi.org/10.1142/s2591728519500208.
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This paper collects the state of the art and the tremendous progress that has been made in hybrid modeling of aeroacoustic sound. Hybrid modeling is defined such that flow and acoustics are modeled separate and connected by an aeroacoustic model. The contributions will be classified with respect to the aeroacoustic models being developed, covering Lighthill’s analogy, Ffowcs Williams and Hawkings, vortex sound, linearized Euler equations (LEE), and different perturbation equations modeling flow induced sound. Within each topic, specific applications, such as jet noise, aircraft noise, ground mobility, noise, fan noise and human phonation, are covered. We focus on the accomplishments and provide the authors’ contribution to aeroacoustic research. Eventually, a concise summary of the different methods and their capabilities is included.
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Morfey, C. L., and M. C. M. Wright. "Extensions of Lighthill's acoustic analogy with application to computational aeroacoustics." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2085 (June 19, 2007): 2101–27. http://dx.doi.org/10.1098/rspa.2007.1864.
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Lighthill's aeroacoustic analogy is formulated for bounded domains in a general way that allows pressure-based alternatives to the fluid density as wave variable. The advantage relative to the standard version (Ffowcs Williams & Hawkings 1969 Phil. Trans. R. Soc. A 264 , 321–342) is that the equivalent surface source terms needed for boundary value problems do not involve the local density. Difficulties encountered in computational aeroacoustics with standard wave extrapolation procedures, due to advection of density inhomogeneities across the control surface, are thereby avoided. Likewise, in initial-value problems, the equivalent volume source terms that represent initial conditions do not involve the density either. The paper ends with an extension to parallel shear flows, in which a modified aeroacoustic analogy due to Goldstein (Goldstein 2001 J. Fluid Mech . 443 , 231–236) is formulated for bounded domains using a similar windowed-variable approach. The results provide a basis for acoustic wave extrapolation from jets and boundary layers, where the control surface cuts through a sheared mean flow.
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Lallier-Daniels, Dominic, Mélanie Piellard, Bruno Coutty, and Stéphane Moreau. "Aeroacoustic study of an axial engine cooling module using lattice-Boltzmann simulations and the Ffowcs Williams and Hawkings’ analogy." European Journal of Mechanics - B/Fluids 61 (January 2017): 244–54. http://dx.doi.org/10.1016/j.euromechflu.2016.10.008.
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Kholodov, Pavel, and Stéphane Moreau. "Identification of Noise Sources in a Realistic Turbofan Rotor Using Large Eddy Simulation." Acoustics 2, no. 3 (September 22, 2020): 691–706. http://dx.doi.org/10.3390/acoustics2030037.
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Large Eddy Simulation is performed using the NASA Source Diagnostic Test turbofan at approach conditions (62% of the design speed). The simulation is performed in a periodic domain containing one fan blade (rotor-alone configuration). The aerodynamic and acoustic results are compared with experimental data. The dilatation field and the dynamic mode decomposition (DMD) are employed to reveal the noise sources around the rotor. The trailing-edge radiation is effective starting from 50% of span. The strongest DMD modes come from the tip region. Two major noise contributors are shown, the first being the tip noise and the second being the trailing-edge noise. The Ffowcs Williams and Hawkings’ (FWH) analogy is used to compute the far-field noise from the solid surface of the blade. The analogy is computed for the full blade, for its tip region (outer 20% of span) and for lower 80% of span to see the contribution of the latter. The acoustics spectrum below 6 kHz is dominated by the tip part (tip noise), whereas the rest of the blade (trailing-edge noise) contributes more beyond that frequency.
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Zhu, Chunli, Hassan Hemida, Dominic Flynn, Chris Baker, Xifeng Liang, and Dan Zhou. "Numerical simulation of the slipstream and aeroacoustic field around a high-speed train." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 231, no. 6 (April 4, 2016): 740–56. http://dx.doi.org/10.1177/0954409716641150.
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The flow field and sound propagation around a three-coach 1/8th scale high-speed passenger train were obtained using a detached-eddy simulation and the Ffowcs-Williams and Hawkings acoustic analogy. The Reynolds number of flow based on the train height and speed was 2,000,000. The numerical results of the flow and aeroacoustic fields were validated using wind tunnel experiments and full-scale data, respectively. Features of overall sound pressure level, sound pressure level and A-weighted sound pressure level of typical measuring points are discussed. The sound propagated by a high-speed train is shown as a broadband noise spectrum including tonal component, where high sound pressure levels are concentrated on the low-frequency range from 10 Hz to 300 Hz. The inter-carriage gap is found to cause distinct tonal noise in contrast to the other parts of the train that cause a broadband noise. The negative log law has been used to study the influence of distance from the centre of track on the sound pressure level, where a good fit is shown at low-frequency ranges. The peak values of A-weighted sound pressure level from both full-scale experiment and simulation results occur at approximately 1 kHz, where simulation results show almost the same range as the experiment. The surface of each component of the train as well as the whole train are chosen as the integral surface for the Ffowcs-Williams and Hawkings computation of the far-field noise characteristics. It was found that the sound source generated by a high-speed train is mainly dipole, and the largest noise was obtained from the leading bogie. The results of this paper provide, for the first time, a better understanding of the aeroacoustic field around a three-coach train model, and the paper has the potential to assist engineers to design high-speed trains with aeroacoustic noise reduction in a better manner.
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Hamiga, Władysław Marek, and Wojciech Bronisław Ciesielka. "Aeroaocustic Numerical Analysis of the Vehicle Model." Applied Sciences 10, no. 24 (December 18, 2020): 9066. http://dx.doi.org/10.3390/app10249066.
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Understanding local phenomena connected with airflow around road vehicles allows to reduce the negative impact of transportation on the environment. This paper presents using numerical tools for Computational Fluid Dynamics (CFD) and Computational AeroAcoustic (CAA) calculation. As a model for simulation, simplified car geometry is used, which is known in the research community as an Ahmed body. The study is divided into two main parts: a validation process and a CAA analysis using the Ffowcs Williams–Hawkings (FW-H) analogy. Research is performed using k−ω Shear Stress Transport (SST) and the Large Eddy Simulation (LES) turbulence model. To compare results with other authors’ studies, three different comparison criteria are introduced: a drag coefficient for different velocities, characteristic flow structure, and velocity profiles. The CAA analysis is presented using colormaps and Fast Fourier Transformation (FFT). The methods used in this work allow visualizing the acoustic field around reference geometry and determining the frequency range for which the A-weighted sound pressure level is the highest.
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Morfey, C. L., S. V. Sorokin, and G. Gabard. "The effects of viscosity on sound radiation near solid surfaces." Journal of Fluid Mechanics 690 (December 1, 2011): 441–60. http://dx.doi.org/10.1017/jfm.2011.449.
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AbstractAlthough the acoustic analogy developed by Lighthill, Curle, and Ffowcs Williams and Hawkings for sound generation by unsteady flow past solid surfaces is formally exact, it has become accepted practice in aeroacoustics to use an approximate version in which viscous quadrupoles are neglected. Here we show that, when sound is radiated by non-rigid surfaces, and the smallest dimension is comparable to or less than the viscous penetration depth, neglect of the viscous-quadrupole term can cause large errors in the sound field. In addition, the interpretation of the viscous quadrupoles as contributing only to sound absorption is shown to be inaccurate. Comparisons are made with the scalar wave equation for linear waves in a viscous fluid, which is extended using generalized functions to describe the effects of solid surfaces. Results are also presented for two model problems, one in a half-space and one with simple cylindrical geometry, for which analytical solutions are available.
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Semiletov, Vasily A., and Sergey A. Karabasov. "A volume integral implementation of the Goldstein generalised acoustic analogy for unsteady flow simulations." Journal of Fluid Mechanics 853 (August 23, 2018): 461–87. http://dx.doi.org/10.1017/jfm.2018.572.
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A new volume integral method based on the Goldstein generalised acoustic analogy is developed and directly applied with large-eddy simulation (LES). In comparison with the existing Goldstein generalised acoustic analogy implementations, the current method does not require the computation and recording of the expensive fluctuating stress autocovariance function in the seven-dimensional space–time. Until now, the multidimensional complexity of the generalised acoustic analogy source term has been the main barrier to using it in routine engineering calculations. The new method only requires local pointwise stresses as an input that can be routinely computed during the flow simulation. On the other hand, the new method is mathematically equivalent to the original Goldstein acoustic analogy formulation, and, thus, allows for a direct correspondence between different effective noise sources in the jet and the far-field noise spectra. The implementation is performed for conditions of a high-speed subsonic isothermal jet corresponding to the Rolls-Royce SILOET experiment and uses the LES solution based on the CABARET solver. The flow and noise solutions are validated by comparison with experiment. The accuracy and robustness of the integral volume implementation of the generalised acoustic analogy are compared with those based on the standard Ffowcs Williams–Hawkings surface integral method and the conventional Lighthill acoustic analogy. As a demonstration of its capabilities to investigate jet noise mechanisms, the new integral volume method is applied to analyse the relative importance of various noise generation and propagation components within the Goldstein generalised acoustic analogy model.
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Zhang, X., X. X. Chen, and C. L. Morfey. "Acoustic Radiation from a Semi-Infinite Duct With a Subsonic Jet." International Journal of Aeroacoustics 4, no. 1-2 (January 2005): 169–84. http://dx.doi.org/10.1260/1475472053730075.
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The radiation of high-order spinning modes from a semi-infinite exhaust duct is studied numerically. The issues involved have applications to noise radiation from the exhaust duct of an aircraft engine. The numerical method is based on solutions of linearised Euler equations (LEE) for propagation in the duct and near field, and the acoustic analogy for far field radiation. A 2.5D formulation of a linearised Euler equation model is employed to accommodate a single spinning mode propagating over an axisymmetric mean flow field. In the solution process, acoustic waves are admitted into the propagation area surrounding the exit of an axisymmetric duct and its immediate downstream area. The wave admission is realised through an absorbing non-reflecting boundary treatment, which admits incoming waves and damps spurious waves generated by the numerical solutions. The wave propagation is calculated through solutions of linearised Euler equations, using an optimised prefactored compact scheme for spatial discretisation. Far field directivity is estimated by solving the Ffowcs Williams-Hawkings equations. The far field prediction is compared with analytic solutions with good agreement.
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Su, Zhongya, Enbin Liu, Yawen Xu, Ping Xie, Chen Shang, and Qiyong Zhu. "Flow field and noise characteristics of manifold in natural gas transportation station." Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 74 (2019): 70. http://dx.doi.org/10.2516/ogst/2019038.
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Manifolds play a role of pressure balance, buffering and rectification for different branch pipelines, the flow noise of manifolds has been a serious problem all this time in natural gas transmission station. By changing the number of outlet pipes of manifolds and the different positions of intake pipes, the distribution of the Sound Pressure Level (SPL) of the manifold flow noise is analyzed based on the Ffowcs Williams-Hawkings (FW-H) acoustic analogy theory and Large Eddy Simulations (LESs). The three-dimensional simulation analysis of the flow field shows that pressure pulsation is the mainly source of manifold noise, as the number of outlet pipe increases, the SPLs of fluid dynamic noise at the end of inlet pipes are significantly reduced by about 10 dB on average, when the inlet and outlet piping are oppositely connected, the SPL is 2 dB~3 dB lower than that in staggered connections. An expansion-chamber muffler is designed with the analysis of its noise reduction effect, the results show that after the muffler is installed, the noise reduction in the low-frequency ranges reaches up to 37.5 dB, which controls the maximum noise to around 82 dB.
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Boudet, Jérôme, Nathalie Grosjean, and Marc C. Jacob. "Wake-Airfoil Interaction as Broadband Noise Source: A Large-Eddy Simulation Study." International Journal of Aeroacoustics 4, no. 1-2 (January 2005): 93–115. http://dx.doi.org/10.1260/1475472053730093.
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A large-eddy simulation is carried out on a rod-airfoil configuration and compared to an accompanying experiment as well as to a RANS computation. A NACA0012 airfoil (chord c = 0.1 m) is located one chord downstream of a circular rod (diameter d = c/10, Red = 48 000). The computed interaction of the resulting sub-critical vortex street with the airfoil is assessed using averaged quantities, aerodynamic spectra and proper orthogonal decomposition (POD) of the instantaneous flow fields. Snapshots of the flow field are compared to particle image velocimetry (PIV) data. The acoustic far field is predicted using the Ffowcs Williams & Hawkings acoustic analogy, and compared to the experimental far field spectra. The large-eddy simulation is shown to accurately represent the deterministic pattern of the vortex shedding that is described by POD modes 1 & 2 and the resulting tonal noise also compares favourably to measurements. Furthermore higher order POD modes that are found in the PIV data are well predicted by the computation. The broadband content of the aerodynamic and the acoustic fields is consequently well predicted over a large range of frequencies ([0 kHz; 10 kHz]).
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MÖHRING, H. Christian, Thomas STEHLE, Kamil GÜZEL, and Christoph ZIZELMANN. "NUMERICAL FLOW SIMULATION OF ROTATING CIRCULAR SAW BLADES FOR THE INVESTIGATION OF SOUND GENERATION MECHANISMS." Journal of Machine Engineering Vol.18, No.1 (February 22, 2018): 62–72. http://dx.doi.org/10.5604/01.3001.0010.8823.
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Emission of airborne sound in the production industry is endangering the employees’ health and is lowering productivity. Circular saw blades in particular cause high sound pressure levels. Therefore, the tool geometry of saw blades should be improved in the sense that the emission of airborne sound is lowered. In this work, the basics for the tool optimization regarding the emission of airborne sound are elaborated. To avoid high costs for various prototypes and experimental investigations, a computational fluid dynamics (CFD) simulation is used. By this, the effects of the adjustments of the geometry on the fluid mechanics can be researched efficiently. Using the acoustic analogy of Ffowcs-Williams/Hawkings, the results of the numerical flow simulation are converted into the sound pressure level. To validate the calculated results, previously conducted experiments are used for comparison. The calculated results correspond well to the values from the experimental measurements. Hence, it is possible to use the developed method to predict the influence of geometry adjustments on the acoustic behaviour, making the optimization process possible. In an outlook, the concept for an optimization loop is explained, which couples the CFD simulation with a parameterized geometry model and an evaluation algorithm.
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Moreau, Stéphane, and Michel Roger. "Advanced noise modeling for future propulsion systems." International Journal of Aeroacoustics 17, no. 6-8 (July 28, 2018): 576–99. http://dx.doi.org/10.1177/1475472x18789005.
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In order to meet noise specifications for future foreseen aircraft propulsion systems, such as for ultrahigh bypass ratio turbofans and contra-rotating open rotors, the dominant turbomachinery noise mechanisms need to be modeled accurately at an early design stage. Two novel methods are presented here, which could significantly improve the existing analytical noise models. For the high-solidity ultrahigh bypass ratio, a mode-matching technique based on a modal expansion of acoustic and vortical variables in each subdomain of a blade row is shown to accurately reproduce sound generation and propagation in two-dimensional bifurcated channels and in three-dimensional annular unstaggered flat-plate cascades. For the low solidity contra-rotating open rotors, several extensions to Amiet’s compressible isolated airfoil theory are coupled with Curle’s and Ffowcs Williams and Hawkings’ acoustic analogy in the frequency domain within a strip theory framework, to yield both far-field tonal and broadband noise. Including sweep in both tonal and broadband noise models is shown to significantly improve the comparison with experiments on a stationary swept airfoil in a uniform turbulent stream and on a realistic contra-rotating open rotor geometry at approach conditions.
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Luo, Bo, Wuli Chu, Song Yan, Zhengjing Shen, and Haoguang Zhang. "Assessment of improved delayed detached eddy simulation in predicting unsteady flows and sound around a circular cylinder." Modern Physics Letters B 35, no. 23 (July 8, 2021): 2150384. http://dx.doi.org/10.1142/s021798492150384x.
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Unsteady flows in the field of engineering are usually calculated by the Unsteady Reynolds-Averaged Navier–Stokes (URANS) owing to the low requirements for computational efforts. However, the numerical resolution of URANS, especially in predicting the unsteady wake flows and sound, is still questionable. In this work, unsteady flow and sound calculations of a circular cylinder are carried out using Improved Delayed Detached Eddy Simulation (IDDES) and the Ffowcs Williams–Hawkings (FW-H) analogy. The predicted results of this calculation are compared with those from the previous studies in the literature in terms of the mean and RMS of the velocity components as well as the sound pressure. The results show that IDDES retains much of the numerical accuracy of the Large Eddy Simulation (LES) approach in predicting unsteady flows and noise while requiring a reduced computational resources in comparison to LES. It is believed that the IDDES can be applied to calculate the complex unsteady flows and flow generated sound with reasonable accuracy in engineering field, which can be used as a promising method for scale-resolving simulations to avoid the expensive computational requirements of LES.
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Guo, H., YS Wang, F. Zhu, NN Liu, and C. Yang. "Multi-field coupling prediction for improving aeroacoustic performance of muffler based on LES and FW-H acoustic analogy methods." International Journal of Aeroacoustics 20, no. 3-4 (March 24, 2021): 414–36. http://dx.doi.org/10.1177/1475472x211005409.
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Based on the large eddy simulation (LES) and Ffowcs Williams and Hawkings (FW-H) equation, a multi-field coupling method is presented for aeroacoustic prediction of a muffler with high-speed and high-temperature exhaust gasflow. A three-dimensional finite-volume model of the muffler is established by using the LES and FW-H acoustic analogy (FW-H-AA) methods. Experimental validations of the simulated results suggest a good accuracy of the combined LES and FW-H-AA approach. Some factors influencing on noise attenuation, such as the gasflow velocity, temperature and the structural parameters of the muffler are analyzed. The results show that the aerodynamic noise and turbulent kinetic energy (TKE) are mainly attributed to the structural mutations in the muffler. The outlet sound pressure level (SPL) increases with the inlet gasflow velocity and decreases with temperature. According to the factor analysis results, the target muffler is modified by adding a fillet transition to the end of inserted tube and redesigning the structures where the TKE concentrated for improving the aerodynamic performance. In terms of the outlet SPL, the inner TKE and the backpressure of the muffler, the modified muffler is significantly improved by the maximum reductions of 3-5dB in SPL, 10–20% in TKE and 0.5–2.5 kPa in backpressure. The presented method might be extended to other kinds of muffler for aeroacoustic calculation and improvement design.
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Dang, Zhigao, Zhaoyong Mao, Baowei Song, and Wenlong Tian. "Noise Characteristics Analysis of the Horizontal Axis Hydrokinetic Turbine Designed for Unmanned Underwater Mooring Platforms." Journal of Marine Science and Engineering 7, no. 12 (December 17, 2019): 465. http://dx.doi.org/10.3390/jmse7120465.
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Operating horizontal axis hydrokinetic turbine (HAHT) generates noise affecting the ocean environment adversely. Therefore, it is essential to determine the noise characteristics of such types of HAHT, as large-scale turbine sets would release more noise pollution to the ocean. Like other rotating machinery, the hydrodynamic noise generated by the rotating turbine has been known to be the most important noise source. In the present work, the transient turbulent flow field of the HAHT is obtained by incompressible large eddy simulation, thereafter, the Ffowcs Williams and Hawkings acoustic analogy formulation is carried out to predict the noise generated from the pressure fluctuations of the blade surface. The coefficient of power is compared with the experimental results, with a good agreement being achieved. It is seen from the pressure contours that the 80% span of the blade has the most severe pressure fluctuations, which concentrate on the region of leading the edge of the airfoil and the suction surface of the airfoil. Then, the noise characteristics around a single turbine are systematically studied, in accordance with the results of the flow field. The noise characteristics around the whole turbine are also investigated to determine the directionality of the noise emission of HAHT.
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Liu, Hanru, Yangang Wang, Jinjia Wei, and Zhiguo Qu. "The importance of controlling the upstream body wake in tandem cylinders system for noise reduction." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 232, no. 3 (December 9, 2016): 517–31. http://dx.doi.org/10.1177/0954410016682271.
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This work numerically investigates the importance of controlling the wake of upstream body in the tandem cylinders aiming at aerodynamics noise reduction. The two-dimensional unsteady Reynolds-averaged Navier–Stokes approach with the k–ω turbulence model and Ffowcs Williams–Hawkings method are employed to simulate the flow field and the aerodynamics noise, respectively. The flow in the porous media is calculated by a volume-averaged model. Analogy to the mass-spring-damper system, one preliminary model is proposed to reveal the key role of stabilizing the upstream body wake. The simulations of different porous materials coating designs are implemented to corroborate the model and provide more details of flow modification by porous materials coating. Results indicate that the porous materials coating designed on the upstream cylinder can decrease the wake impingement on the downstream cylinder via suppressing the vortex shedding. Subsequently, not only the tonal noise but also the broadband noise level of tandem system can be reduced. It is also clarified that the effects of downstream cylinder absorption and downstream cylinder wake control by porous materials coating is not comparable with the upstream cylinder wake control. The present study gives a new idea to flow control and noise reduction of the multibody systems considering efficiency and economy.
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Souri, Mohammad, Farshad Moradi Kashkooli, Madjid Soltani, and Kaamran Raahemifar. "Effect of Upstream Side Flow of Wind Turbine on Aerodynamic Noise: Simulation Using Open-Loop Vibration in the Rod in Rod-Airfoil Configuration." Energies 14, no. 4 (February 22, 2021): 1170. http://dx.doi.org/10.3390/en14041170.
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Adaptive and flexible control techniques have recently been examined as methods of controlling flow and reducing the potential noise in vertical axis wind turbines. Two-Dimensional (2D) fluid flow simulation around rod-airfoil is addressed in this study as a simple component of the wind turbine by using Unsteady Reynolds Averaged Navier–Stokes (URANS) equations for prediction of noise using Ffowcs Williams-Hawkings (FW-H) analogy. To control the flow and reduce noise, the active controlling vibration rod method is utilized with a maximum displacement ranging from 0.01 C to 1 C (C: airfoil chord). Acoustic assessment indicates that the leading edge of the blade produces noise, that by applying vibration in cylinder, blade noise in 0.1 C and 1 C decreases by 22 dB and 35 dB, respectively. Applying vibration is aerodynamically helpful since it reduces the fluctuations in the airfoil lift force by approximately 48% and those in the rod by about 46%. Strouhal assessment (frequency) shows that application of control is accompanied by 20% increase. Applying vibration in the rod reduces the flow fluctuations around the blade, thus reduces the wind turbine blade noise. This idea, as a simple example, can be used to study the incoming flow to turbines and their blades that are affected by the upstream flow.
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Posson, H., and N. Peake. "The acoustic analogy in an annular duct with swirling mean flow." Journal of Fluid Mechanics 726 (June 10, 2013): 439–75. http://dx.doi.org/10.1017/jfm.2013.210.
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AbstractThis paper is concerned with modelling the effects of swirling flow on turbomachinery noise. We develop an acoustic analogy to predict sound generation in a swirling and sheared base flow in an annular duct, including the presence of moving solid surfaces to account for blade rows. In so doing we have extended a number of classical earlier results, including Ffowcs Williams & Hawkings’ equation in a medium at rest with moving surfaces, and Lilley’s equation for a sheared but non-swirling jet. By rearranging the Navier–Stokes equations we find a single equation, in the form of a sixth-order differential operator acting on the fluctuating pressure field on the left-hand side and a series of volume and surface source terms on the right-hand side; the form of these source terms depends strongly on the presence of swirl and radial shear. The integral form of this equation is then derived, using the Green’s function tailored to the base flow in the (rigid) duct. As is often the case in duct acoustics, it is then convenient to move into temporal, axial and azimuthal Fourier space, where the Green’s function is computed numerically. This formulation can then be applied to a number of turbomachinery noise sources. For definiteness here we consider the noise produced downstream when a steady distortion flow is incident on the fan from upstream, and compare our results with those obtained using a simplistic but commonly used Doppler correction method. We show that in all but the simplest case the full inclusion of swirl within an acoustic analogy, as described in this paper, is required.
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Lyrintzis, Anastasios S. "Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field." International Journal of Aeroacoustics 2, no. 2 (April 2003): 95–128. http://dx.doi.org/10.1260/147547203322775498.
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A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface Ffowcs-Williams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field CFD data. Both methods can be extended in order to include refraction effects outside the control surface. The methods have been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A simple set of portable Kirchhoff/FW-H subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field CFD code.
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Díaz, Argüelles K. M., Oro J. M. Fernández, E. Blanco Marigorta, and C. Santolaria Morros. "Numerical prediction of tonal noise generation in an inlet vaned low-speed axial fan using a hybrid aeroacoustic approach." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 223, no. 9 (June 2, 2009): 2081–98. http://dx.doi.org/10.1243/09544062jmes1426.
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This work presents a numerical prediction of the tonal noise generation in a single-stage, axial flow fan, using a hybrid approach that first calculates the noise sources (generation) using conventional computational fluid dynamics (CFD) techniques, and then estimates the noise level in the blower far-field region (propagation) by means of an aeroacoustic analogy. As a starting point, an unsteady three-dimensional full-annulus simulation of the internal flow is carried out, using a wall-modelled large eddy simulation (WMLES) scheme for the turbulence closure to identify the acoustic sources. A well-tested commercial CFD package, FLUENT, was employed for that purpose, so a complete set of unsteady forces exerted over the blades was calculated. Following, a generalization of Lighthill's aeroacoustic analogy, the so-called Ffowcs Williams and Hawkings (FFWH) aeroacoustic analogy, was numerically implemented using a C++algorithm to resolve an integral formulation of the free-field FFWH wave equation, where CFD data are included in the source terms. The major contribution was expected to be found in the estimation of the tonal noise levels, directly linked to the intensity of the stator—rotor interaction phenomena. Additionally, intensive experimental measurements in the noise propagation region of the fan were conducted, in order to validate the numerical study. A reasonable agreement was found in the tonal noise spectra, although important discrepancies appeared due to the attenuation produced by the fan casing, not considered in the numerical model. Although limitations in the current computational resources led to the use of a relatively coarse mesh in the CFD modelling, the numerical study provided valuable information about the particular influence of the tonal noise sources, estimating accordingly overall experimental trends, and showing the potentiality of numerical tools to deal with noise control for designers and researchers.
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Alqash, Sultan, Sharvari Dhote, and Kamran Behdinan. "Predicting Far-Field Noise Generated by a Landing Gear Using Multiple Two-Dimensional Simulations." Applied Sciences 9, no. 21 (October 23, 2019): 4485. http://dx.doi.org/10.3390/app9214485.
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In this paper, a new approach is proposed to predict the far-field noise of a landing gear (LG) based on near-field flow data obtained from multiple two-dimensional (2D) simulations. The LG consists of many bluff bodies with various shapes and sizes. The analysis begins with dividing the LG structure into multiple 2D cross-sections (C-Ss) representing different configurations. The C-Ss locations are selected based on the number of components, sizes, and geometric complexities. The 2D Computational Fluid Dynamics (CFD) analysis for each C-S is carried out first to obtain the acoustic source data. The Ffowcs Williams and Hawkings acoustic analogy (FW-H) is then used to predict the far-field noise. To compensate for the third dimension, a source correlation length (SCL) is assumed based on a perfectly correlated flow. The overall noise of the LG is calculated as the incoherent sum of the predicted noise from all C-Ss. Flow over a circular cylinder is then studied to examine the effect of the 2D CFD results on the predicted noise. The results are in good agreement with reported experimental and numerical data. However, the Strouhal number (St) is over-predicted. The proposed approach provides a reasonable estimation of the LG far-field noise at a low computational cost. Thus, it has the potential to be used as a quick tool to predict the far-field noise from an LG during the design stage.
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Zhang, Yadong, Jiye Zhang, Tian Li, Liang Zhang, and Weihua Zhang. "Research on Aerodynamic Noise Reduction for High-Speed Trains." Shock and Vibration 2016 (2016): 1–21. http://dx.doi.org/10.1155/2016/6031893.
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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.
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Rasekh, Sepehr, and Saeed Karimian. "Effect of solidity on aeroacoustic performance of a vertical axis wind turbine using improved delayed detached eddy simulation." International Journal of Aeroacoustics 20, no. 3-4 (March 25, 2021): 390–413. http://dx.doi.org/10.1177/1475472x211003299.
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Vertical axis wind turbines (VAWTs) can be suitably installed in urban regions. Although the power performance is essential, the noise generated by a VAWT may influence the living environment. An accurate prediction of power and noise performance is therefore necessary. In the present study, a precise aerodynamic and aeroacoustic performance assessment of a Darrieus VAWT is accomplished with the aim of exploring the effect of solidity parameter using a high-fidelity method. The improved delayed detached eddy simulation (IDDES) and the Ffowcs Williams and Hawkings (FW-H) acoustic analogy approaches have been utilized for predicting flow field and noise level. The simulations were performed in three different solidities at a specific tip speed ratio (TSR). It is shown that changing the solidity parameter affects both power and noise level remarkably. Change in the aerodynamic performance mostly occurs due to variation in instantaneous effective angle of attack which comprises many detailed discussions. The lower the solidity the higher the value of effective angle of attack. The noise level also affects by changing solidity as consequence of flow field variation. It is discussed here how the noise level would alter in terms of solidity, TSR, distance and azimuth angle. As the solidity increases, the sound pressure level (SPL) at blade pass frequency increases. Since design of quieter VAWT with application in urban regions recently is of the most interest and importance therefore such deep studies could appropriately address hybrid criteria and be helpful in future investigations.
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Wolf, William R., João Luiz F. Azevedo, and Sanjiva K. Lele. "Convective effects and the role of quadrupole sources for aerofoil aeroacoustics." Journal of Fluid Mechanics 708 (August 10, 2012): 502–38. http://dx.doi.org/10.1017/jfm.2012.327.
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AbstractThe present investigation of aerofoil self-noise generation and propagation concerns the effects of mean flow and quadrupole sources on the broadband noise that arises from the interaction of turbulent boundary layers with the aerofoil trailing edge and the tonal noise that arises from vortex shedding generated by laminar boundary layers and trailing-edge bluntness. Compressible large-eddy simulations (LES) are conducted for a NACA0012 aerofoil with rounded trailing edge for four flow configurations with different angles of incidence, boundary layer tripping configurations and free-stream Mach numbers. The Reynolds number based on the aerofoil chord is fixed at ${\mathit{Re}}_{c} = 408\hspace{0.167em} 000$. The acoustic predictions are performed by the Ffowcs Williams & Hawkings (FWH) acoustic analogy formulation and incorporate convective effects. Surface and volume integrations of dipole and quadrupole source terms appearing in the FWH equation are performed using a three-dimensional wideband multi-level adaptive fast multipole method (FMM) in order to accelerate the calculations of aeroacoustic integrals. In order to validate the numerical solutions, flow simulation and acoustic prediction results are compared to experimental data available in the literature and good agreement is observed in terms of both aerodynamic and aeroacoustic results. For low-Mach-number flows, quadrupole sources can be neglected in the FWH equation and mean flow effects appear only for high frequencies. However, for higher speeds, convection effects are relevant for all frequencies and quadrupole sources have a more pronounced effect for medium and high frequencies. The convective effects are most readily observed in the upstream direction.
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Zhong, Siyang, and Xin Zhang. "A generalized sound extrapolation method for turbulent flows." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2210 (February 2018): 20170614. http://dx.doi.org/10.1098/rspa.2017.0614.
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Sound extrapolation methods are often used to compute acoustic far-field directivities using near-field flow data in aeroacoustics applications. The results may be erroneous if the volume integrals are neglected (to save computational cost), while non-acoustic fluctuations are collected on the integration surfaces. In this work, we develop a new sound extrapolation method based on an acoustic analogy using Taylor’s hypothesis (Taylor 1938 Proc. R. Soc. Lon. A 164 , 476–490. ( doi:10.1098/rspa.1938.0032 )). Typically, a convection operator is used to filter out the acoustically inefficient components in the turbulent flows, and an acoustics dominant indirect variable D c p ′ is solved. The sound pressure p ′ at the far field is computed from D c p ′ based on the asymptotic properties of the Green’s function. Validations results for benchmark problems with well-defined sources match well with the exact solutions. For aeroacoustics applications: the sound predictions by the aerofoil–gust interaction are close to those by an earlier method specially developed to remove the effect of vortical fluctuations (Zhong & Zhang 2017 J. Fluid Mech. 820 , 424–450. ( doi:10.1017/jfm.2017.219 )); for the case of vortex shedding noise from a cylinder, the off-body predictions by the proposed method match well with the on-body Ffowcs-Williams and Hawkings result; different integration surfaces yield close predictions (of both spectra and far-field directivities) for a co-flowing jet case using an established direct numerical simulation database. The results suggest that the method may be a potential candidate for sound projection in aeroacoustics applications.
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Markesteijn, A. P., and S. A. Karabasov. "Simulations of co-axial jet flows on graphics processing units: the flow and noise analysis." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2159 (October 14, 2019): 20190083. http://dx.doi.org/10.1098/rsta.2019.0083.
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Large-eddy simulations (LES) are performed for a range of perfectly expanded co-axial jet cases corresponding to conditions of the computation of coaxial jet noise (CoJeN) experiment by QinetiQ. In all simulations, the high-resolution Compact Accurately Boundary-Adjusting high-REsolution Technique (CABARET) is used for solving the Navier–Stokes equations on unstructured meshes. The Ffowcs Williams–Hawkings method based on the penetrable integral surfaces is applied for far-field noise predictions. To correctly model the turbulent flow downstream of the complex nozzle that includes a central body, a wall modelled LES approach is implemented together with a turbulent inflow condition based on synthetic turbulence. All models are run on graphics processing units to enable a considerable reduction of the flow solution time in comparison with the conventional LES. The flow and noise solutions are validated against the experimental data available with 1–2 dB accuracy being reported for noise spectra predictions on the fine grid. To analyse the structure of effective noise sources of the jets, the covariance of turbulent fluctuating Reynolds stresses is computed and their characteristic scales are analysed in the context of the generalized acoustic analogy jet noise models. Motivated by self-similarity of single-stream axi-symmetric jet flows, a suitable non-dimensionalization of the effective jet noise sources of the CoJeN jets is tested, and its implications for low-order jet noise models are discussed. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.
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Liu, Enbin, Shanbi Peng, and Tiaowei Yang. "Noise-silencing technology for upright venting pipe jet noise." Advances in Mechanical Engineering 10, no. 8 (August 2018): 168781401879481. http://dx.doi.org/10.1177/1687814018794819.
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When a natural gas transmission and distribution station performs a planned or emergency venting operation, the jet noise produced by the natural gas venting pipe can have an intensity as high as 110 dB, thereby severely affecting the production and living environment. Jet noise produced by venting pipes is a type of aerodynamic noise. This study investigates the mechanism that produces the jet noise and the radiative characteristics of jet noise using a computational fluid dynamics method that combines large eddy simulation with the Ffowcs Williams–Hawkings acoustic analogy theory. The analysis results show that the sound pressure level of jet noise is relatively high, with a maximum level of 115 dB in the low-frequency range (0–1000 Hz), and the sound pressure level is approximately the average level in the frequency range of 1000–4000 Hz. In addition, the maximum and average sound pressure levels of the noise at the same monitoring point both slightly decrease, and the frequency of the occurrence of a maximum sound pressure level decreases as the Mach number at the outlet of the venting pipe increases. An increase in the flow rate can result in a shift from low-frequency to high-frequency noise. Subsequently, this study includes a design of an expansion-chamber muffler that reduces the jet noise produced by venting pipes and an analysis of its effectiveness in reducing noise. The results show that the expansion-chamber muffler designed in this study can effectively reduce jet noise by 10–40 dB and, thus, achieve effective noise prevention and control.
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Stark, Callum, and Weichao Shi. "Hydroacoustic and hydrodynamic investigation of bio-inspired leading-edge tubercles on marine-ducted thrusters." Royal Society Open Science 8, no. 9 (September 2021): 210402. http://dx.doi.org/10.1098/rsos.210402.
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Underwater radiated noise (URN) has a negative impact on the marine acoustic environment where it can disrupt marine creature's basic living functions such as navigation and communication. To control the ambient ocean noise levels due to human activities, international governing bodies such as the International Maritime Organization (IMO) have issued non-mandatory guidelines to address this issue. Under such framework, the hydroacoustic performance of marine vehicles has become a critical factor to be evaluated and controlled throughout the vehicles' service life in order to mitigate the URN level and the role humankind plays in the ocean. This study aims to apply leading-edge (LE) tubercles of the humpback whales’ pectoral fins to a benchmark ducted propeller to investigate its potential in noise mitigation. This was conducted using CFD, where the high-fidelity improved delayed detached eddy simulations (IDDES) in combination with the porous Ffowcs-Williams Hawkings (FW-H) acoustic analogy was used to solve the hydrodynamic flow field and propagate the generated noise to the far-field. It has been found that the LE tubercles have shown promising noise mitigation capabilities in the far-field, where the OASPL at J = 0.1 was reduced to a maximum of 3.4 dB with a maximum of 11 dB reduction in certain frequency ranges at other operating conditions. Based on detailed flow analysis researching the fundamental vortex dynamics, this noise reduction is shown to be due to the disruption of the coherent turbulent wake structure in the propeller slipstream causing the acceleration in the dissipation of turbulence and vorticity-induced noise.
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Hattori, Yuji, and Ryu Komatsu. "Mechanism of aeroacoustic sound generation and reduction in a flow past oscillating and fixed cylinders." Journal of Fluid Mechanics 832 (October 26, 2017): 241–68. http://dx.doi.org/10.1017/jfm.2017.668.
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The aeroacoustic sound generated in a flow past two cylinders, one of which is oscillating and the other is fixed, is studied by direct numerical simulation. This problem involves key ingredients of the aeroacoustic noise generated from wind turbines, helicopters, axial flow fans and other turbomachinery: flow, a moving body and a fixed body. The corrected volume penalization method is successfully applied to resolve the sound pressure of aeroacoustic waves as a solution of the compressible Navier–Stokes equations. The sound pressure was shown to be in good agreement with the prediction by the Ffowcs Williams–Hawkings aeroacoustic analogy, which takes account of the cylinder motion, confirming the accuracy of the corrected volume penalization method. Prior to the case of two cylinders, sound generation in flow past a single oscillating cylinder is considered. The fluid motion can be either periodic or non-periodic depending on the frequency and the amplitude of cylinder oscillation. The acoustic power is significantly reduced when the fluid motion locks in to a frequency lower than the natural frequency of vortex shedding from a fixed cylinder. When a fixed cylinder is added, the acoustic power depends strongly on the distance between the cylinders, since that determines whether synchronization occurs and the phase difference between the three forces: the lift forces exerted on the two cylinders and the inertial force due to volume displacement effect of the oscillating cylinder. In particular, significant sound reduction is observed when the fixed cylinder is placed upstream and the frequency of the cylinder oscillation is set to the frequency for which the acoustic power is minimized in the single-cylinder case.
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Delbari, Seyed Hamid, Amir Nejat, Mohammad H. Ahmadi, Ali Khaleghi, and Marjan Goodarzi. "Numerical modeling of aeroacoustic characteristics of different savonius blade profiles." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 6 (June 19, 2019): 3349–69. http://dx.doi.org/10.1108/hff-12-2018-0764.
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Purpose This study aims to carry out numerical modeling to predict aerodynamic noise radiation from four different Savonius rotor blade profile. Design/methodology/approach Incompressible unsteady reynolds-averaged navier-stokes (URANS) approach using gamma–theta turbulence model is conducted to obtain the time accurate turbulent flow field. The Ffowcs Williams and Hawkings (FW-H) acoustic analogy formulation is used for noise predictions at optimal tip speed ratio (TSR). Findings The mean torque and power coefficients are compared with the experimental data and acceptable agreement is observed. The total and Mono+Dipole noise graphs are presented. A discrete tonal component at low frequencies in all graphs is attributed to the blade passing frequency at the given TSR. According to the noise prediction results, Bach type rotor has the lowest level of noise emission. The effect of TSR on the noise level from the Bach rotor is investigated. A direct relation between angular velocity and the noise emission is found. Practical implications The savonius rotor is a type of vertical axis wind turbines suited for mounting in the vicinity of residential areas. Also, wind turbines wherein operation are efficient sources of tonal and broadband noises and affect the inhabitable environment adversely. Therefore, the acoustic pollution assessment is essential for the installation of wind turbines in residential areas. Originality/value This study aims to investigate the radiated noise level of four common Savonius rotor blade profiles, namely, Bach type, Benesh type, semi-elliptic and conventional. As stated above, numbers of studies exploit the URANS method coupled with the FW-H analogy to predict the aeroacoustics behavior of wind turbines. Therefore, this approach is chosen in this research to deal with the aeroacoustics and aerodynamic calculation of the flow field around the aforementioned Savonius blade profiles. The effect of optimal TSR on the emitted noise and the contribution of thickness, loading and quadrupole sources are of interest in this study.
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Zhu, JY, ZW Hu, and DJ Thompson. "The flow and flow-induced noise behaviour of a simplified high-speed train bogie in the cavity with and without a fairing." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 232, no. 3 (February 22, 2017): 759–73. http://dx.doi.org/10.1177/0954409717691619.
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Aerodynamic noise is a significant source for high-speed trains but its prediction in an industrial context is difficult to achieve. In this article, the flow and aerodynamic noise behaviour of a simplified high-speed train bogie at scale 1:10 are studied through numerical simulations. The bogie is situated in a cavity beneath the train and the influence of a bogie fairing on the flow and flow-induced noise that developed around the bogie area is investigated. A two-stage hybrid method is used, which combines the computational fluid dynamics and an acoustic analogy. The near-field unsteady flow is obtained by solving the unsteady three-dimensional Navier–Stokes equations numerically using delayed detached-eddy simulation, and the data are utilised to predict the far-field noise based on the Ffowcs Williams–Hawkings acoustic analogy. Results show that when the bogie is located inside the bogie cavity, the shear layer developed from the leading edges of the cavity interacts strongly with the flow separated from the upstream components of the bogie and the cavity walls. Therefore, a highly turbulent flow is generated within the bogie cavity due to the strong flow impingements and flow recirculations occurring there. For the case without the fairing, the surface shape discontinuity in the bogie cavity along the carbody sidewalls generates strong flow unsteadiness around these regions. When the fairing is mounted in front of the bogie cavity, the flow interactions between the bogie cavity and the outer region are reduced and the development of turbulence outside the fairing is greatly weakened. Based on the predictions of the noise radiated to the trackside using a permeable data surface parallel to the carbody sidewall, it has been found that the bogie fairing is effective in reducing the noise generated in most of the frequency range, and a noise reduction of around 5 dB is achieved in the farfield for the current model case.
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Abdessemed, Chawki, Abdessalem Bouferrouk, and Yufeng Yao. "Aerodynamic and Aeroacoustic Analysis of a Harmonically Morphing Airfoil Using Dynamic Meshing." Acoustics 3, no. 1 (March 6, 2021): 177–99. http://dx.doi.org/10.3390/acoustics3010013.
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This work explores the aerodynamic and aeroacoustic responses of an airfoil fitted with a harmonically morphing Trailing Edge Flap (TEF). An unsteady parametrization method adapted for harmonic morphing is introduced, and then coupled with dynamic meshing to drive the morphing process. The turbulence characteristics are calculated using the hybrid Stress Blended Eddy Simulation (SBES) RANS-LES model. The far-field tonal noise is predicted using the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy method with corrections to account for spanwise effects using a correlation length of half the airfoil chord. At various morphing frequencies and amplitudes, the 2D aeroacoustic tonal noise spectra are obtained for a NACA 0012 airfoil at a low angle of attack (AoA = 4°), a Reynolds number of 0.62 × 106, and a Mach number of 0.115, respectively, and the dominant tonal frequencies are predicted correctly. The aerodynamic coefficients of the un-morphed configuration show good agreement with published experimental and 3D LES data. For the harmonically morphing TEF case, results show that it is possible to achieve up to a 3% increase in aerodynamic efficiency (L/D). Furthermore, the morphing slightly shifts the predominant tonal peak to higher frequencies, possibly due to the morphing TEF causing a breakup of large-scale shed vortices into smaller, higher frequency turbulent eddies. It appears that larger morphing amplitudes induce higher sound pressure levels (SPLs), and that all the morphing cases induce the shift in the main tonal peak to a higher frequency, with a maximum 1.5 dB reduction in predicted SPL. The proposed dynamic meshing approach incorporating an SBES model provides a reasonable estimation of the NACA 0012 far-field tonal noise at an affordable computational cost. Thus, it can be used as an efficient numerical tool to predict the emitted far-field tonal noise from a morphing wing at the design stage.
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De Gennaro, Michele, Helmut Kühnelt, and Alessandro Zanon. "Numerical Prediction of the Tonal Airborne Noise for a NACA 0012 Aerofoil at Moderate Reynolds Number Using a Transitional URANS Approach." Archives of Acoustics 42, no. 4 (December 20, 2017): 653–75. http://dx.doi.org/10.1515/aoa-2017-0069.
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Abstract Tonal airborne noise of aerofoils appears in a limited range of moderate Reynolds numbers and angles of attack. In these specific conditions, the aerofoil is characterised by a large region of laminar flow over the aerodynamic surface, typically resulting in two-dimensional laminar instabilities in the boundary layer, generating one or more acoustic tones. The numerical simulation of such phenomenon requires, beside an accurate prediction of the unsteady flow field, a proper modelling of the laminar to turbulent transition of the boundary layer, which generally imposes the use of highly CPU demanding approaches such as large eddy simulation (LES) or direct numerical simulation (DNS). This paper aims at presenting the results of numerical experiments for evaluating the capability of capturing the tonal airborne noise by using an advanced, yet low computationally demanding, unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence model augmented with a transitional model to account for the laminar to turbulent transition. This approach, coupled with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy, is adopted for predicting the far-field acoustic sound pressure of a NACA 0012 aerofoil with Reynolds number ranging from 0.39 · 106 to 1.09 · 106. The results show a main tone located approximately at 1.6-1.8 kHz for a Reynolds number equal to 0.62 · 106, increasing to 2.4 kHz at Reynolds number equal to 0.85 · 106 and 3.4 kHz at 1.09 · 106, while no main tones are observed at 0.39 · 106. The computed spectra confirm that the acoustic emission of the aerofoil is dominated by tonal structures and that the frequency of the main tone depends on the Reynolds number consistently with the ladder-like tonal structure suggested by Paterson et al. Moreover, in specific conditions, the acoustic spectra exhibit a multi-tonal structure visible in narrowband spectra, in line with the findings of Arbey and Bataille. The presented results demonstrate the capability of the numerical model of predicting the physics of the tonal airborne noise generation.
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Avallone, F., W. C. P. van der Velden, D. Ragni, and D. Casalino. "Noise reduction mechanisms of sawtooth and combed-sawtooth trailing-edge serrations." Journal of Fluid Mechanics 848 (June 8, 2018): 560–91. http://dx.doi.org/10.1017/jfm.2018.377.
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Trailing-edge serrations are add ons retrofitted to wind-turbine blades to mitigate turbulent boundary-layer trailing-edge noise. This manuscript studies the physical mechanisms behind the noise reduction by investigating the far-field noise and the hydrodynamic flow field. A conventional sawtooth and a combed-sawtooth trailing-edge serration are studied. Combed-sawtooth serrations are obtained by filling the empty space between the teeth with combs (i.e. solid filaments). Both serration geometries are retrofitted to a NACA 0018 aerofoil at zero degree angle of attack. Computations are carried out by solving the explicit, transient, compressible lattice Boltzmann equation, while the acoustic far field is obtained by means of the Ffowcs Williams and Hawkings analogy. The numerical results are validated against experiments. It is confirmed that the combed-sawtooth serrations reduce noise more than the conventional sawtooth ones for the low- and mid-frequency range. It is found that the presence of combs affects the intensity of the scattered noise but not the frequency range of noise reduction. For both configurations, the intensity of the surface pressure fluctuations decreases from the root to the tip, and noise sources are mainly located at the serrations root for the low- and mid-frequency range. The presence of the filaments generates a more uniform distribution of the noise sources along the edges with respect to the conventional serration. The installation of combs mitigates the interaction between the two sides of the aerofoil at the trailing edge and the generation of a turbulent wake in the empty space between teeth. As a result, the inward (i.e. from the serration edge to the centreline) and outward (i.e. from the serration centreline to the edge) flow motions, due to the presence of the teeth, are mitigated. It is found that the installation of serrations affects the surface pressure fluctuations integral parameters. Both the spanwise correlation length and convective velocity of the surface pressure fluctuations increase with respect to the baseline straight configuration. When both quantities are similar to the one obtained for the straight trailing edge, the effect of the slanted edge is negligible, thus corresponding to no noise reduction. It is concluded that the changes in sound radiation are mainly caused by destructive interference of the radiated sound waves for which a larger spanwise correlation length is beneficial. Finally, the difference between measurements and the literature is caused by an incorrect modelling of the spanwise correlation length, which shows a different decay rate with respect to the one obtained for a straight trailing edge.
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Mao, Yijun, and Zhiwei Hu. "Acoustic Analogy for Multiphase or Multicomponent Flow." Journal of Vibration and Acoustics 140, no. 2 (October 4, 2017). http://dx.doi.org/10.1115/1.4037702.
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The Ffowcs Williams and Hawkings (FW-H) equation is widely used to predict sound generated from flow and its interaction with impermeable or permeable surfaces. Owing to the Heaviside function used, this equation assumes that sound only propagates outside the surface. In this paper, we develop a generalized acoustic analogy to account for sound generation and propagation both inside and outside the surface. The developed wave equation provides an efficient mathematical approach to predict sound generated from multiphase or multicomponent flow (MMF) and its interaction with solid boundaries. The developed wave equation also clearly interprets the physical mechanisms of sound generation, emphasizing that the monopole and dipole sources are dependent on the jump in physical quantities across the interface of MMF rather than the physical quantities on one-side surface expressed in the FW-H equation. The sound generated from gas bubbles in water is analyzed by the newly developed wave equation to investigate parameters affecting the acoustic power output, showing that the acoustic power feature concluded from the Crighton and Ffowcs Williams (C-FW) equation is only valid in a specific case of all bubbles oscillating in phase.
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Marsan, Aurélien, and Stéphane Moreau. "Aeroacoustic Analysis of the Tonal Noise of a Large-Scale Radial Blower." Journal of Fluids Engineering 140, no. 2 (October 19, 2017). http://dx.doi.org/10.1115/1.4037976.
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Large-scale radial blowers are widely used in factories and are one of the main sources of noise. The present study aims at identifying the noise generation mechanisms in such a radial blower in order to suggest simple modifications that could be made in order to reduce the noise. The flow in a representative large-scale radial blower is investigated thanks to unsteady Reynolds-averaged Navier–Stokes (URANS) numerical simulations. The radiated noise is calculated, thanks to an in-house propagation code based on the Ffowcs Williams Hawkings' (FWH) analogy, SherFWH. The results highlight the main noise generation mechanisms, in particular the interaction between the rotating blades and the tongue, and the interaction between the rotating blades and the trapdoors located on the volute sidewall. Some modifications of the geometry are suggested.
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Orselli, R. Marcondes, B. Souza Carmo, and R. Lauterjung Queiroz. "Noise predictions of the advanced noise control fan model using lattice Boltzmann method and Ffowcs Williams–Hawkings analogy." Journal of the Brazilian Society of Mechanical Sciences and Engineering 40, no. 1 (January 2018). http://dx.doi.org/10.1007/s40430-018-0982-2.
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Joong Kim, Seung, and Hyung Jin Sung. "Design of the Solenoid Valve of an Antilock Braking System With Reduced Flow Noise." Journal of Fluids Engineering 140, no. 3 (October 27, 2017). http://dx.doi.org/10.1115/1.4038088.
Full textAbstract:
Large eddy simulations are carried out to predict the flow noise produced in the solenoid valve of an antilock braking system (ABS) using Lighthill’s acoustic analogy and the Ffowcs Williams and Hawkings (FW–H) surface integral method. The fluid inside the valve is assumed to be incompressible at a fixed temperature. The solenoid valve operation is realized by applying an overset grid methodology to the moving plunger, and the plunger has a linear motion in the axial direction. Several types of solenoid valves are numerically designed to maximally reduce the flow noise. The upstream flow is detached through a small opening between the plunger and the seat, which generates pressure fluctuation around the narrow gap, which is subject to high wall pressure fluctuations and shear stresses. Large eddy simulations are performed by varying the position of the flow separation. An optimal design of the valve is obtained, featuring a small radius of surface curvature, a smooth surface, and a large plunger tip area angle. Measurements are obtained from the optimal design to validate the design in a real vehicle performance test, and the predicted pressure frequency in the solenoid valve agreed well with the experimental results.
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Ballesteros-Tajadura, Rafael, Sandra Velarde-Suárez, and Juan Pablo Hurtado-Cruz. "Noise Prediction of a Centrifugal Fan: Numerical Results and Experimental Validation." Journal of Fluids Engineering 130, no. 9 (August 12, 2008). http://dx.doi.org/10.1115/1.2953229.
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Centrifugal fans are widely used in several applications, and in some cases, the noise generated by these machines has become a serious problem. The centrifugal fan noise is frequently dominated by tones at the blade passing frequency as a consequence of the strong interaction between the flow discharged from the impeller and the volute tongue. In this study, a previously published aeroacoustic prediction methodology (Cho, Y., and Moon, Y.J., 2003, “Discrete Noise Prediction of Variable Pitch Cross-Flow Fans by Unsteady Navier-Stokes Computations,” ASME J. Fluids Eng., 125, pp. 543–550) has been extended to three-dimensional turbulent flow in order to predict the noise generated by a centrifugal fan. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been carried out using the computational fluid dynamics code FLUENT®. The unsteady forces applied by the fan blades to the fluid are obtained from the data provided by the simulation. The Ffowcs Williams and Hawkings model extension of Lighthill’s analogy has been used to predict the aerodynamic noise generated by the centrifugal fan from these unsteady forces. Also, the noise generated by the fan has been measured experimentally, and the experimental results have been compared to the numerical results in order to validate the aerodynamic noise prediction methodology. Reasonable agreement has been found between the numerical and the experimental results.
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Kim, Hogun, Zhiwei Hu, and David Thompson. "Effect of different typical high speed train pantograph recess configurations on aerodynamic noise." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, August 10, 2020, 095440972094751. http://dx.doi.org/10.1177/0954409720947516.
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For high-speed trains, the aerodynamic noise becomes an essential consideration in the train design. The pantograph and pantograph recess are recognised as important sources of aerodynamic noise. This paper studies the flow characteristics and noise contributions of three typical high-speed train roof configurations, namely a cavity, a ramped cavity and a flat roof with side insulation plates. The Improved Delayed Detached-Eddy Simulation approach is used for the flow calculations and the Ffowcs Williams & Hawkings aeroacoustic analogy is used for far-field acoustic predictions. Simulations are presented for a simplified train body at 1/10 scale and 300 km/h with these three roof configurations. In each case, two simplified pantographs (one retracted and one raised) are located on the roof. Analysis of the flow fields obtained from numerical simulations clearly shows the influence of the train roof configuration on the flow behaviour, including flow separations, reattachment and vortex shedding, which are potential noise sources. A highly unsteady flow occurs downstream when the train roof has a cavity or ramped cavity due to flow separation at the cavity trailing edge, while vortical flow is generated by the side insulation plates. For the ramped cavity configuration, moderately large pressure fluctuations appear on the cavity outside walls in the upstream region due to unsteady flow from the upstream edge of the plate. The raised pantograph, roof cavity, and ramped cavity are identified as the dominant noise sources. When the retracted pantograph is located in the ramped roof cavity, its noise contribution is less important. Furthermore, the insulation plates also generate tonal components in the noise spectra. Of the three configurations considered, the roof cavity configuration radiates the least noise at the side receiver in terms of A-weighted level.
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Buchwald, Patrick, Damian M. Vogt, Julien Grilliat, Wolfgang Laufer, Michael B. Schmitz, Andreas Lucius, and Marc Schneider. "Aeroacoustic Analysis of Low-Speed Axial Fans With Different Rotational Speeds in the Design Point." Journal of Engineering for Gas Turbines and Power 140, no. 5 (November 14, 2017). http://dx.doi.org/10.1115/1.4038122.
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One of the main design decisions in the development of low-speed axial fans is the right choice of the blade loading versus rotational speed, since a target pressure rise could either be achieved with a slow spinning fan and high blade loading or a fast spinning fan with less flow turning in the blade passages. Both the blade loading and the fan speed have an influence on the fan performance and the fan acoustics, and there is a need to find the optimum choice in order to maximize efficiency while minimizing noise emissions. This paper addresses this problem by investigating five different fans with the same pressure rise but different rotational speeds in the design point (DP). In the first part of the numerical study, the fan design is described and steady-state Reynolds-averaged Navier–Stokes (RANS) simulations are conducted in order to identify the performance of the fans in the DP and in off-design conditions. The investigations show the existence of an optimum in rotational speed regarding fan efficiency and identify a flow separation on the hub causing a deflection of the outflow in radial direction as the main loss source for slow spinning fans with high blade loadings. Subsequently, large eddy simulations (LES) along with the acoustic analogy of Ffowcs Williams and Hawkings (FW–H) are performed in the DP to identify the main noise sources and to determine the far-field acoustics. The identification of the noise sources within the fans in the near-field is performed with the help of the power spectral density (PSD) of the pressure. In the far-field, the sound power level (SWL) is computed using different parts of the fan surface as FW–H sources. Both methods show the same trends regarding noise emissions and allow for a localization of the noise sources. The flow separation on the hub is one of the main noise sources along with the tip vortex with an increase in its strength toward lower rotational speeds and higher loading. Furthermore, a horseshoe vortex detaching from the rotor leading edge and impinging on the pressure side as well as the turbulent boundary layer on the suction side represent significant noise sources. In the present investigation, the maximum in efficiency coincides with the minimum in noise emissions.