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Author: Alison Zilstra
Publisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 79
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Book Description
Aeroacoustic noise from wind turbines is often an obstacle in the implementation of wind farms. Reduction of this noise is key to allowing the expansion of the wind energy sector which is crucial for decreasing the dependence on fossil fuel energy sources. The use of a fully analytical computational model for aeroacoustic noise will allow for acoustics to be incorporated into the design stage of new wind turbine technologies. This thesis investigates the use of a predictive model for the noise from two dimensional (2D) blade segments using computational fluid dynamics (CFD). The simulation uses Reynolds Averaged Navier-Stokes (RANS) to initialize the simulation, and then a combination of Large Eddy Simulation (LES) and the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy to predict the flow and acoustics, respectively. The SD 7037 and NACA 0012 airfoils were simulated and compared against experimental flow and acoustics data. The SD 7037 airfoil was tested using incompressible and compressible LES simulation for a Reynolds number of Re=4.25x104. The results show good prediction of both the flow and acoustics, and the source of the tonal noise generated by the airfoil at 0° angle of attack (AOA) was determined to be a result of 2D boundary layer behaviour, and also the transition from 2D to 3D behaviour. The 1° AOA results did not predict the tonal noise found in experiments, but it was determined that inaccuracies in some of the simulations caused the boundary layer behaviour to falsely change to that of the experimental 2° or 3° AOA. The NACA 0012 airfoil was tested using incompressible LES for a high Re case of Re=1.5x106. The flow simulation for this case was good, however the acoustic prediction was at a higher sound pressure level (SPL) than the experimental data. The second case of this simulation predicted tonal noise when experiments predicted broadband noise only. The simulation of this false tonal noise was attributed to instabilities in the simulation. The differences between the SD 7037 1° results, where instabilities caused no tones to be simulated, and the NACA 0012 results for the second case, where instabilities caused false tones to be predicted, shows that care must be taken in the setup of the simulation. Recommendations for future work are to perform a grid independence study and sensitivity analysis to determine the cause of these false predictions. That being said, overall, the predictive abilities of the computational aeroacoustic model result in good prediction of the airfoil self-noise for static AOAs.
Author: Alison Zilstra
Publisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 79
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Book Description
Aeroacoustic noise from wind turbines is often an obstacle in the implementation of wind farms. Reduction of this noise is key to allowing the expansion of the wind energy sector which is crucial for decreasing the dependence on fossil fuel energy sources. The use of a fully analytical computational model for aeroacoustic noise will allow for acoustics to be incorporated into the design stage of new wind turbine technologies. This thesis investigates the use of a predictive model for the noise from two dimensional (2D) blade segments using computational fluid dynamics (CFD). The simulation uses Reynolds Averaged Navier-Stokes (RANS) to initialize the simulation, and then a combination of Large Eddy Simulation (LES) and the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy to predict the flow and acoustics, respectively. The SD 7037 and NACA 0012 airfoils were simulated and compared against experimental flow and acoustics data. The SD 7037 airfoil was tested using incompressible and compressible LES simulation for a Reynolds number of Re=4.25x104. The results show good prediction of both the flow and acoustics, and the source of the tonal noise generated by the airfoil at 0° angle of attack (AOA) was determined to be a result of 2D boundary layer behaviour, and also the transition from 2D to 3D behaviour. The 1° AOA results did not predict the tonal noise found in experiments, but it was determined that inaccuracies in some of the simulations caused the boundary layer behaviour to falsely change to that of the experimental 2° or 3° AOA. The NACA 0012 airfoil was tested using incompressible LES for a high Re case of Re=1.5x106. The flow simulation for this case was good, however the acoustic prediction was at a higher sound pressure level (SPL) than the experimental data. The second case of this simulation predicted tonal noise when experiments predicted broadband noise only. The simulation of this false tonal noise was attributed to instabilities in the simulation. The differences between the SD 7037 1° results, where instabilities caused no tones to be simulated, and the NACA 0012 results for the second case, where instabilities caused false tones to be predicted, shows that care must be taken in the setup of the simulation. Recommendations for future work are to perform a grid independence study and sensitivity analysis to determine the cause of these false predictions. That being said, overall, the predictive abilities of the computational aeroacoustic model result in good prediction of the airfoil self-noise for static AOAs.
Author: Thomas F. Brooks
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 148
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Book Description
Author: William Roberto Wolf
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 238
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Book Description
The development of physics-based noise prediction tools for analysis of aerodynamic noise sources is of paramount importance since noise regulations have become more stringent. Direct simulation of aerodynamic noise remains prohibitively expensive for engineering problems because of the resolution requirements. Therefore, hybrid approaches that consist of predicting nearfield flow quantities by a suitable CFD simulation and farfield sound radiation by aeroacoustic integral methods are more attractive. In this work, we apply the fast multipole method (FMM) to accelerate the solution of boundary integral equation methods such as the boundary element method (BEM) and the Ffowcs Williams & Hawkings (FWH) acoustic analogy formulation. The FMM-BEM is implemented for the solution of acoustic scattering problems and the effects of non-uniform potential flows on acoustic scattering are investigated. The FMM-FWH is implemented for the solution of two and three-dimensional problems of sound propagation. The effects of flow convection and non-linear quadrupole sources are assessed through the study of sound generated by unsteady laminar flows. Finally, a hybrid methodology is applied for the investigation of airfoil noise. This study is important for the design of aerodynamic shapes such as wings and high-lift devices, as well as wind turbine blades, fans and propellers. The present investigation of airfoil self-noise generation and propagation concerns the broadband noise that arises from the interaction of turbulent boundary layers with the airfoil trailing edge and tonal noise that arises from vortex shedding generated by laminar boundary layers. Nearfield acoustic sources are computed using compressible large eddy simulation (LES) and acoustic predictions are performed by the FMM-FWH. Numerical simulations are conducted for a NACA0012 airfoil with tripped boundary layers and blunt rounded trailing edge at different Mach numbers and angles of incidence. The effects of non-linear quadrupole sources and convection are assessed. In order to validate the numerical solutions, flow simulation and acoustic prediction results are compared to experimental data available in the literature and excellent agreement is observed.
Author: Nicholas Tam
Publisher:
ISBN:
Category : Aeroacoustics
Languages : en
Pages : 165
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Book Description
The current study addresses the issue of noise relating to both large and small scale wind turbines. In utility scale applications, larger size rotors in new generations of wind turbines bring an increasing challenge to manage noise emissions. A better understanding of wind turbine noise characteristics, behaviour and generation mechanics can facilitate the development of noise reduction strategies. This can greatly aid in their adoption. The issue of noise, however, is not exclusive to large scale wind turbines. Small scale wind turbines, operating in laminar or transitional regimes, has the potential to emit tonal noise which can be more audible and of a greater nuisance. Small scale wind turbines can be installed in higher traffic areas closer to human receptors. As such, the understanding of their noise characteristics, behaviour and generation mechanics is important as well. In Reynolds number regime where small scale wind turbine operates, tonal noise is primarily caused by laminar boundary layer-vortex shedding (LBL-VS) noise generation mechanism. In the controlled environment of a closed circuit wind tunnel, the SD-7037 airfoil profile is examined at Re = 4.0 x 10^4. Acoustic measurements are collected when the airfoil is under dynamic oscillation and under various static angles of attack. Results found evidence to suggest LBL-VS noise originated from the suction side of the airfoil in this study; suggesting noise reduction efforts should be focused on suction side phenomenon in similar low Reynold number flow (Re
Author: E. Manoha
Publisher:
ISBN:
Category :
Languages : en
Pages : 15
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Book Description
The numerical prediction of the aerodynamic noise radiated by an isolated airfoil is performed using a Computational AeroAcoustics (CAA) method. This hybrid method combines (i) a simulation of the near field unsteady flow and (ii) an acoustic method to estimate the noise radiated in the far field. This process is applied to a symmetrical NACA0012 airfoil with a constant section and a blunted trailing edge (TE), at a Mach number of 0.205 and an angle-of-attack of 5%. The Reynolds number based on the airfoil chord is 2%86 millions. The computational domain has a spanwise extent representing 3.3 % of the chord.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722933173
Category :
Languages : en
Pages : 146
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Book Description
A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given. Brooks, Thomas F. and Pope, D. Stuart and Marcolini, Michael A. Langley Research Center AEROACOUSTICS; AERODYNAMIC NOISE; AIRFOIL PROFILES; AIRFOILS; BLADE-VORTEX INTERACTION; BOUNDARY LAYER SEPARATION; BOUNDARY LAYERS; NOISE PREDICTION (AIRCRAFT); VORTEX SHEDDING; AERODYNAMIC STALLING; APPLICATIONS PROGRAMS (COMPUTERS); NOISE MEASUREMENT; NOISE SPECTRA; ROTARY WINGS; STROUHAL NUMBER; TRAILING EDGES; VORTICES; WIND TUNNEL TESTS...
Author: Sheryl M. Grace
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: David P. Lockard
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Harvey H. Hubbard
Publisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 620
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721529681
Category :
Languages : en
Pages : 26
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Book Description
Accurate prediction of jet fan and exhaust plume flow and noise generation and propagation is very important in developing advanced aircraft engines that will pass current and future noise regulations. In jet fan flows as well as exhaust plumes, two major sources of noise are present: large-scale, coherent instabilities and small-scale turbulent eddies. In previous work for the NASA Glenn Research Center, three strategies have been explored in an effort to computationally predict the noise radiation from supersonic jet exhaust plumes. In order from the least expensive computationally to the most expensive computationally, these are: 1) Linearized Euler equations (LEE). 2) Very Large Eddy Simulations (VLES). 3) Large Eddy Simulations (LES). The first method solves the linearized Euler equations (LEE). These equations are obtained by linearizing about a given mean flow and the neglecting viscous effects. In this way, the noise from large-scale instabilities can be found for a given mean flow. The linearized Euler equations are computationally inexpensive, and have produced good noise results for supersonic jets where the large-scale instability noise dominates, as well as for the tone noise from a jet engine blade row. However, these linear equations do not predict the absolute magnitude of the noise; instead, only the relative magnitude is predicted. Also, the predicted disturbances do not modify the mean flow, removing a physical mechanism by which the amplitude of the disturbance may be controlled. Recent research for isolated airfoils' indicates that this may not affect the solution greatly at low frequencies. The second method addresses some of the concerns raised by the LEE method. In this approach, called Very Large Eddy Simulation (VLES), the unsteady Reynolds averaged Navier-Stokes equations are solved directly using a high-accuracy computational aeroacoustics numerical scheme. With the addition of a two-equation turbulence model and the use of a relatively c
