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This paper extends previously published TNO-Blake methods to predict airfoil broadband self-noise due to interaction of a turbulent boundary-layer with a sharp trailing edge. The method presented herein combines Blake's model to p...
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This paper extends previously published TNO-Blake methods to predict airfoil broadband self-noise due to interaction of a turbulent boundary-layer with a sharp trailing edge. The method presented herein combines Blake's model to predict surface pressure fluctuations and Amiet model to predict trailing edge noise emission. The Blake method is based on the solution of the Poisson equation as an integral of the mean-shear turbulent source interaction, over the entire boundary layer thickness. A recent advances in description of streamwise turbulent intensity are employed to avoid tuning parameters. Surface pressure spectra are measured with remote microphones and compared to the prediction. In the next step, the wavenumber-frequency spectrum as predicted by the TNO model was utilized as an input to the Amiet model to evaluate the far-field trailing edge noise. Agreement between measurements and both predictions are generally within 2 dB.
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Wind turbine noise is one of the main factors that limit the widespread exploitation of wind energy. The periodic 'swishing' character of wind turbine noise is often reported as an important factor in explaining its relatively hig...
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Wind turbine noise is one of the main factors that limit the widespread exploitation of wind energy. The periodic 'swishing' character of wind turbine noise is often reported as an important factor in explaining its relatively high annoyance compared to other sound sources of roughly the same level [1, 2]. Swishing is the result of an amplitude modulation of the broadband aerodynamic noise, which occurs at the blade passing frequency, and is typically about 1 Hz for modern large horizontal-axis wind turbines. This paper has three objectives: The first is to present a new tool for the analysis of wind turbine noise data and swishing noise in particular. It is based on cyclostationary analysis, which is ideally suited to the analysis of data whose statistics vary periodically in time. The second is to present a prediction method based on Amiet's model of rotor noise. It is based on the concept of instantaneous spectrum from which the time variation of the noise spectrum may be deduced. Noise predictions from this model will be compared against the cyclostationary measurements from a modern wind turbine. The third is to develop an index to assess the swishing noise of wind turbine. A relative simple algebraic formulation is proposed to formulate this index, which is of use in the understanding of wind turbine swishing character.
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Global interest in urban air mobility and small multi-rotor unmanned aerial systems is rapidly growing. Multi-rotors can fly in every direction, horizontally and vertically, and hover. However, the acoustic signature of these vehi...
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Global interest in urban air mobility and small multi-rotor unmanned aerial systems is rapidly growing. Multi-rotors can fly in every direction, horizontally and vertically, and hover. However, the acoustic signature of these vehicles is of great concern. In the present study, the modelling of tonal noise components is implemented in a three-step approach. In the first and the second steps, the method requires modelling the steady and the unsteady components of aerodynamic loads, respectively. Steady aerodynamic loads are estimated with Blade Element Momentum Theory and XFOIL panel code, whereas the unsteady deterministic components are modelled with either Sears or Loewy functions. In the third step, the harmonic noise components are predicted. Aerodynamic loads and tonal noise components are modelled and compared with experiments conducted in the newly established anechoic chamber at the Faculty of Aerospace Engineering at the Technion - Israel Institute of Technology. The second and the third sound harmonics are predicted with high accuracy. The satisfactory agreement of thrust, torque and tonal noise results concerning the experimental measurements validated the proposed approach for predicting performances and noise radiation associated with low-Reynolds number propellers at the engineering level. The work can be seen as the infrastructure for rotor design.
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This paper investigates the TNO type models for predicting the surface pressure spectrum underneath the turbulent boundary layer, which is considered the acoustic source for trailing edge noise. Two airfoil test cases, namely, NAC...
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This paper investigates the TNO type models for predicting the surface pressure spectrum underneath the turbulent boundary layer, which is considered the acoustic source for trailing edge noise. Two airfoil test cases, namely, NACA0015 and NACA0012, have been investigated using the flow solutions obtained from RANS and XFOIL at various Reynolds number and attack angles. Airfoil boundary layer flows are strongly influenced by the pressure gradient's existence, the influence of which has been accounted for in this paper by improving the previously published anisotropic stretching coefficient definition. Additionally, we introduce the influence of pressure gradient in the velocity spectrum by scaling the integral correlation length with the kinematic shape factor. We apply this new approach and present a new model which fully accounts for pressure gradient and frequency dependency in the velocity spectrum. The predictions of the new model are in good agreement with the published experimental results.
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Acoustic measurements, for example modal decomposition of sound waves in a duct, often require the use of multiple number of microphones. These microphones are flush mounted on the wall of a duct to form a circumferential array at...
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Acoustic measurements, for example modal decomposition of sound waves in a duct, often require the use of multiple number of microphones. These microphones are flush mounted on the wall of a duct to form a circumferential array at different axial locations along the duct. In the conventional calibration method each microphone is calibrated against a reference microphone or with a piston phone. Both the reference microphone and the test microphone are exposed to a known sound pressure level, typically 94 dB (ref. 20μPa). This task of calibrating each microphone individually is very laborious, particularly for many microphones. As a result, it is necessary to use an effective and less time-consuming calibration technique to ensure proper calibration of these microphones, especially with respect to phase. In this paper, a procedure to calibrate simultaneously an array of test microphones, based on cross-spectral matrix, is proposed and evaluated experimentally.
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摘要 :
Acoustic measurements, for example modal decomposition of sound waves in a duct, often require the use of multiple number of microphones. These microphones are flush mounted on the wall of a duct to form a circumferential array at...
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Acoustic measurements, for example modal decomposition of sound waves in a duct, often require the use of multiple number of microphones. These microphones are flush mounted on the wall of a duct to form a circumferential array at different axial locations along the duct. In the conventional calibration method each microphone is calibrated against a reference microphone or with a piston phone. Both the reference microphone and the test microphone are exposed to a known sound pressure level, typically 94 dB (ref. 20μPa). This task of calibrating each microphone individually is very laborious, particularly for many microphones. As a result, it is necessary to use an effective and less time-consuming calibration technique to ensure proper calibration of these microphones, especially with respect to phase. In this paper, a procedure to calibrate simultaneously an array of test microphones, based on cross-spectral matrix, is proposed and evaluated experimentally.
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This paper presents a MATLAB suite of codes entitled getPROP for designing, analyzing, and optimizing low-noise signature propellers. The getPROP package has been developed to perform end-to-end analysis, from an initial propeller...
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This paper presents a MATLAB suite of codes entitled getPROP for designing, analyzing, and optimizing low-noise signature propellers. The getPROP package has been developed to perform end-to-end analysis, from an initial propeller design to a low-signature optimized configuration that meets the operational requirements. The presented getPROP code framework covers various modules: propeller design, aerodynamic database, performance, noise prediction, atmospheric attenuation, psychoacoustic, and optimization. A complete analysis with the getPROP suite is presented through the optimization of a commercial off-the-shelf APC 14" x 5.5" propeller into a low-noise signature design, thus demonstrating the software applicability for improving multi-copters propellers.
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Active Flow Control in the form of steady blowing is used with the aim of reducing the noise generated by high Reynolds number flow over bluff bodies. A Computational Fluid Dynamics solver is used to compute the flow field and pro...
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Active Flow Control in the form of steady blowing is used with the aim of reducing the noise generated by high Reynolds number flow over bluff bodies. A Computational Fluid Dynamics solver is used to compute the flow field and provide surface pressure samples to a Ffowcs Williams-Hawkings solver to obtain far-field acoustic pressure signals. Two geometries are considered, a circular cylinder and a main strut and drag-stay configuration with the upstream drag-stay inclined by 25° towards the upstream direction. The latter is representative of interaction flow occurring in a landing gear. The steady blowing is applied on the cylinder and drag-stay configurations from a slot located on both sides of the body at ±30°, measured from the stagnation line. For the drag-stay configuration, blowing at 180° is also investigated. In the isolated cylinder configuration, the noise reduction obtained by blowing at ±30° is found to be related to a modification of the flow field directly downstream of the cylinder. An increase in the recirculation region length and a reduction of the velocity fluctuations are observed. However, applying the same flow control on the drag-stay configuration results in an increase in the overall noise. Blowing at 180° on the drag-stay component results in a maximum reduction of 8.5 dB at the shedding peak frequency for an observer aligned with the lift dipole to the side of the drag-stay configuration. The self-noise of both components and the interaction noise are reduced.
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摘要 :
Active Flow Control in the form of steady blowing is used with the aim of reducing the noise generated by high Reynolds number flow over bluff bodies. A Computational Fluid Dynamics solver is used to compute the flow field and pro...
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Active Flow Control in the form of steady blowing is used with the aim of reducing the noise generated by high Reynolds number flow over bluff bodies. A Computational Fluid Dynamics solver is used to compute the flow field and provide surface pressure samples to a Ffowcs Williams-Hawkings solver to obtain far-field acoustic pressure signals. Two geometries are considered, a circular cylinder and a main strut and drag-stay configuration with the upstream drag-stay inclined by 25° towards the upstream direction. The latter is representative of interaction flow occurring in a landing gear. The steady blowing is applied on the cylinder and drag-stay configurations from a slot located on both sides of the body at ±30°, measured from the stagnation line. For the drag-stay configuration, blowing at 180° is also investigated. In the isolated cylinder configuration, the noise reduction obtained by blowing at ±30° is found to be related to a modification of the flow field directly downstream of the cylinder. An increase in the recirculation region length and a reduction of the velocity fluctuations are observed. However, applying the same flow control on the drag-stay configuration results in an increase in the overall noise. Blowing at 180° on the drag-stay component results in a maximum reduction of 8.5 dB at the shedding peak frequency for an observer aligned with the lift dipole to the side of the drag-stay configuration. The self-noise of both components and the interaction noise are reduced.
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The differing methodologies employed by Canadian and United Kingdom universities in similar student capstone projects is presented. Polytechnique Montreal, from Canada, employs the Conceive, Design, Implement, Operate approach in ...
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The differing methodologies employed by Canadian and United Kingdom universities in similar student capstone projects is presented. Polytechnique Montreal, from Canada, employs the Conceive, Design, Implement, Operate approach in its teachings. Its aerospace engineering undergraduate students are tasked with an integrative project every year, culminating to a capstone project. The presented project's goal was the design and prototyping of a dynamic test bench of a free motion, three degrees of freedom, 2D airfoil with a full-span flap/aileron for wind tunnel testing in Toulouse, France. The project was conducted in a multidisciplinary environment, under the supervision of local and international collaborators and received industry in-kind support. Similar to Polytechnique, the students at the University of Southampton were tasked with designing and testing a transferable wind tunnel test rig. The experimental test rig was designed to provide a flexible finite-span wing free motion in either a vertical translation or a rotation of the root point. Different numerical modelling approaches were undertaken for comparison with experimental results. The project was developed by consecutive Integrated Masters students with the help of industry specialists and international faculty advisors.
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