Download or read book Airfoil Self Noise and Prediction written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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...
Download or read book Airfoil Self noise and Prediction written by Thomas F. Brooks and published by . This book was released on 1989 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Airfoil Self noise and Prediction written by Thomas F. Brooks and published by . This book was released on 1989 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Prediction of Broadband Self noise of an Airfoil written by Carlos L. Gomez and published by . This book was released on 2006 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Computational Aeroacoustic Prediction of Airfoil Self noise at Static Angles of Attack written by Alison Zilstra and published by . This book was released on 2019 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Large Eddy Simulation of Airfoil Self noise written by Joseph George Kocheemoolayil and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Sustaining the continued growth of aviation is critically dependent on managing its noise emission. Developing tools to predict airframe noise from first principles is a pacing item in this regard. Within this context, noise generated by flow past airfoils constitutes an important canonical problem that is also relevant to a wide variety of other applications such as wind turbine noise, cooling fan noise, turbofan noise, propeller noise and helicopter blade noise. The noise generated by a turbulent flow that encounters the trailing edge of an airfoil is the fundamental component of all these problems. Over the past 15 years, significant strides have been made towards using large eddy simulations (LES) for predicting airfoil noise from first-principles. However, they have largely been restricted to canonical configurations at low Reynolds numbers. Perhaps the restriction to low Reynolds numbers is the most serious limitation since majority of the experiments target full-scale Reynolds numbers making one-to-one comparisons impossible. This thesis focuses on extending the scope of LES based predictions to full-scale Reynolds numbers and non-canonical configurations such as the near-stall and post-stall regimes which have received very limited attention owing to their complexity. Wall-modeled large eddy simulations (WMLES) that combine LES with a model for unresolved near-wall turbulence are used to predict airfoil noise at high Reynolds numbers. The Benchmark Problems for Airframe Noise Computations (BANC) workshop is held every year as part of the AIAA/CEAS Aeroacoustics conference. Category 1 of the workshop targets airfoil trailing edge noise prediction at high Reynolds numbers relevant to engineering applications. No first-principles based approach free of empiricism and tunable coefficients has had success in this category to date. Independently validated far-field noise measurements are available for four configurations in the category. Our simulations predict trailing edge noise accurately for all four configurations. Detailed comparisons are made with dedicated experiments. Insensitivity of the simulation results to important aleatory and epistemic uncertainties is established. Resolution requirements for making accurate noise predictions using WMLES are identified through a systematic grid-refinement study. Developing the capability to predict airfoil noise for near-stall and post-stall configurations is necessary to investigate their suspected responsibility for a phenomenon known as Other Amplitude Modulation (OAM) of wind turbine noise. Predicting the flow past a wind turbine airfoil in the post-stall regime is a formidable challenge in itself. In particular, there is a school of thought that large scale three-dimensionality and extreme sensitivity to the experimental facility are inevitable and preclude the possibility of a fair comparison between simulations and measurements in this regime. However, in agreement with a recent theoretical study our simulation results indicate that the lower lift due to large scale three-dimensionality can be reproduced even in span-periodic simulations if the domain size is sufficiently large. The large span simulation predicts the pressure distribution around the airfoil with unprecedented accuracy. Successful prediction of pressure fluctuations on the airfoil surface beneath the suction side boundary layer is demonstrated in the near-stall and post-stall regimes. Previously unavailable two-point statistics of surface pressure fluctuations are documented.
Download or read book Airfoil Aeroacoustics LES and Acoustic Analogy Predictions written by William Roberto Wolf and published by Stanford University. This book was released on 2011 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book NASA Reference Publication written by and published by . This book was released on 1977 with total page 800 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Airfoil Aeroacoustics LES and Acoustic Analogy Predictions written by William Roberto Wolf and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book NASA Scientific and Technical Publications written by and published by . This book was released on 1990 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Trailing Edge Noise Prediction Using the Non Linear Disturbance Equations written by Abhishek Jain and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: AIRFOIL self-noise consists of five major sources. One of these identified sources is turbulent boundary layer -- trailing edge (TBL-TE) noise, which is an important source of rotor and wind turbine broadband noise, and the focus of this thesis. Trailing edge noise is the result of unsteady flow interacting with the trailing edge of an airfoil or other sharp edged flow surface. The presence of the sharp trailing edge scatters the sound generated by the turbulent eddies very efficiently, especially for sources in the immediate vicinity of the edge. There is a need for accurate and computationally efficient methods to calculate the turbulent boundary layer trailing-edge (TBL-TE) noise that are not reliant on empirical data. The majority of the current semi-empirical techniques are based on measurements from symmetric NACA airfoil sections (i.e. NACA 0012). These techniques are generally not coupled with CFD solvers to obtain turbulent boundary layer data that provides pertinent parameters used in the acoustic calculations. Some methods exist that incorporate CFD solutions like Large Eddy simulations (LES) into their noise prediction algorithms. But these are prohibitively expensive and impractical for routine use. The method described in this paper is a first principles approach that aims to predict the TBL-TE noise using computational aeroacoustic (CAA) techniques without resorting to empiricism.The prediction of trailing edge noise requires an accurate calculation of the boundary layer fluctuations in the vicinity of the trailing edge. Scales in the computational domain ranging from the small turbulent boundary layer scales to those of the long-range noise propagation need to be resolved. These data can be obtained using simulation techniques like Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES). However such simulations for complete helicopters or wind turbine rotors are impractical given today's computational resources. Also, DNS becomes unrealistic for the propagation of the acoustic signal to distant observers. The method described here overcomes these limitations by using a hybrid CAA approach coupled with a flow solver based on the non-linear disturbance equations (NLDE). The overall problem is separated into component problems with the NLDE equations applied over a relatively small noise generating region i.e. approximately the last 10% of the chord or less. This makes the solution more computationally efficient than LES for the full airfoil or rotor and enables the use of the most computationally efficient methods in the required regions. The proposed method is advantageous to helicopter and wind turbine manufacturers as it provides a tool for the prediction of rotor broadband noise at the design stage. This can also be used as a tool to reduce noise through the analysis of appropriate noise reduction devices.
Download or read book Flow Noise written by Con Doolan and published by Springer Nature. This book was released on 2022-05-10 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights the importance of sound produced by fluid flow or flow-induced noise. Noise created by unsteady flow creates high levels of environmental noise pollution, a known public health problem, and can compromise the acoustic qualities of marine vessels. There is a seemingly ever-growing list of modern technology that created flow-induced noise which includes aircraft, wind turbines, submarines, drones, high-speed rail, and cooling fans. More scientists and engineers are required to incorporate the effects of flow-induced noise in their work. This book also provides a comprehensive introduction to the theory underpinning the understanding of flow-induced noise.
Download or read book New Results in Numerical and Experimental Fluid Mechanics VI written by Cameron Tropea and published by Springer Science & Business Media. This book was released on 2007-10-26 with total page 973 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume features the contributions to the 15th Symposium of the STAB (German Aerospace Aerodynamics Association). Papers provide a broad overview of ongoing work in Germany, including high aspect ratio wings, low aspect ratio wings, bluff bodies, laminar flow control and transition, active flow control, hypersonic flows, aeroelasticity, aeroacoustics, mathematical fundamentals, numerical simulations, physical fundamentals, and facilities.
Download or read book Predicting Outdoor Sound written by Keith Attenborough and published by CRC Press. This book was released on 2021-03-07 with total page 690 pages. Available in PDF, EPUB and Kindle. Book excerpt: The second edition of Predicting Outdoor Sound is an up-to-date reference on the propagation of sound close to the ground and its prediction. New content includes comparisons between predictions and data for road traffic, railway and wind turbine noise; descriptions of source characteristics in the HARMONOISE model; propagation over rough seas, parallel low walls, and lattices; outlines of numerical methods; gabion (caged stones) and sonic crystal noise barriers; meteorological effects on noise barrier performance; and the prediction requirements for auralization. The book brings together relevant theories, prediction schemes, and data, thereby providing a basis for determining what model or scheme might be applicable for any situation. It also offers a background on useful analytical approximations and the restrictions, as well as difficulties and limitations associated with engineering prediction schemes. The text should be of considerable interest to researchers in outdoor sound propagation and, more generally, it should provide a comprehensive primer on the topic for lecturers, consultants and students in acoustics and noise control.
Download or read book Wind Turbine Aerodynamics written by Wen Zhong Shen and published by MDPI. This book was released on 2019-10-04 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt: Wind turbine aerodynamics is one of the central subjects of wind turbine technology. To reduce the levelized cost of energy (LCOE), the size of a single wind turbine has been increased to 12 MW at present, with further increases expected in the near future. Big wind turbines and their associated wind farms have many advantages but also challenges. The typical effects are mainly related to the increase in Reynolds number and blade flexibility. This Special Issue is a collection of 21 important research works addressing the aerodynamic challenges appearing in such developments. The 21 research papers cover a wide range of problems related to wind turbine aerodynamics, which includes atmospheric turbulent flow modeling, wind turbine flow modeling, wind turbine design, wind turbine control, wind farm flow modeling in complex terrain, wind turbine noise modeling, vertical axis wind turbine, and offshore wind energy. Readers from all over the globe are expected to greatly benefit from this Special Issue collection regarding their own work and the goal of enabling the technological development of new environmentally friendly and cost-effective wind energy systems in order to reach the target of 100% energy use from renewable sources, worldwide, by 2050
Download or read book New Results in Numerical and Experimental Fluid Mechanics XIII written by Andreas Dillmann and published by Springer Nature. This book was released on 2021-07-13 with total page 787 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book offers timely insights into research on numerical and experimental fluid mechanics and aerodynamics, mainly for (but not limited to) aerospace applications. It reports on findings by members of the STAB (German Aerospace Aerodynamics Association) and DGLR (German Society for Aeronautics and Astronautics) and covers both nationally and EC-funded projects. Continuing on the tradition of the previous volumes, the book highlights innovative solutions, promoting translation from fundamental research to industrial applications. It addresses academics and professionals in the field of aeronautics, astronautics, ground transportation, and energy alike.
Download or read book Advances in Mechanical Engineering and Material Science written by Pankaj Tambe and published by Springer Nature. This book was released on 2023-10-16 with total page 343 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the select proceedings of the Second International Conference on Advances in Mechanical Engineering and Material Science (ICAMEMS 2023). It covers the latest research in broad areas of manufacturing and materials engineering. Various topics covered in this book are advanced manufacturing processes, additive manufacturing, green manufacturing, industry 4.0, conventional machining processes, non-conventional machining processes, micro machining, materials processing surface science and engineering, advanced composite materials, materials characterization, and many more. The book is useful for researchers and students in the various fields of mechanical engineering.
