Large-Eddy Simulation for Acoustics

Large-Eddy Simulation for Acoustics
Author: Claus Wagner
Publisher: Cambridge University Press
Total Pages: 389
Release: 2007-01-15
Genre: Technology & Engineering
ISBN: 1139463160

Noise around airports, trains, and industries attracts environmental concern and regulation. Large-eddy simulation (LES) is used for noise-reduced design and acoustical research. This 2007 book, by 30 experts, presents the theoretical background of acoustics and LES, and details about numerical methods, e.g. discretization schemes, boundary conditions, and coupling aspects.

Computational Aeroacoustics

Computational Aeroacoustics
Author: Jay C. Hardin
Publisher: Springer Science & Business Media
Total Pages: 525
Release: 2012-12-06
Genre: Science
ISBN: 1461383420

Computational aeroacoustics is rapidly emerging as an essential element in the study of aerodynamic sound. As with all emerging technologies, it is paramount that we assess the various opportuni ties and establish achievable goals for this new technology. Essential to this process is the identification and prioritization of fundamental aeroacoustics problems which are amenable to direct numerical siIn ulation. Questions, ranging from the role numerical methods play in the classical theoretical approaches to aeroacoustics, to the correct specification of well-posed numerical problems, need to be answered. These issues provided the impetus for the Workshop on Computa tional Aeroacoustics sponsored by ICASE and the Acoustics Division of NASA LaRC on April 6-9, 1992. The participants of the Work shop were leading aeroacousticians, computational fluid dynamicists and applied mathematicians. The Workshop started with the open ing remarks by M. Y. Hussaini and the welcome address by Kristin Hessenius who introduced the keynote speaker, Sir James Lighthill. The keynote address set the stage for the Workshop. It was both an authoritative and up-to-date discussion of the state-of-the-art in aeroacoustics. The presentations at the Workshop were divided into five sessions - i) Classical Theoretical Approaches (William Zorumski, Chairman), ii) Mathematical Aspects of Acoustics (Rodolfo Rosales, Chairman), iii) Validation Methodology (Allan Pierce, Chairman), iv) Direct Numerical Simulation (Michael Myers, Chairman), and v) Unsteady Compressible Flow Computa tional Methods (Douglas Dwoyer, Chairman).

Computational Acoustics of Noise Propagation in Fluids - Finite and Boundary Element Methods

Computational Acoustics of Noise Propagation in Fluids - Finite and Boundary Element Methods
Author: Steffen Marburg
Publisher: Springer Science & Business Media
Total Pages: 584
Release: 2008-02-27
Genre: Science
ISBN: 3540774483

The book provides a survey of numerical methods for acoustics, namely the finite element method (FEM) and the boundary element method (BEM). It is the first book summarizing FEM and BEM (and optimization) for acoustics. The book shows that both methods can be effectively used for many other cases, FEM even for open domains and BEM for closed ones. Emphasis of the book is put on numerical aspects and on treatment of the exterior problem in acoustics, i.e. noise radiation.

Time-conservative Finite-volume Method with Large-eddy Simulation for Computational Aeroacoustics

Time-conservative Finite-volume Method with Large-eddy Simulation for Computational Aeroacoustics
Author: Orhan Aybay
Publisher:
Total Pages:
Release: 2010
Genre: Acoustical engineering
ISBN:

This thesis presents a time-conservative finite-volume method based on a modern flow simulation technique developed by the author. Its applicability to technically relevant aeroacoustic applications is demonstrated. The time-conservative finite-volume method has unique features and advantages in comparison to traditional methods. The main objectives of this study are to develop an advanced, high-resolution, low dissipation second-order scheme and to simulate the near acoustic field with similar accuracy as higher-order (e.g., 4th-order, 6th-order, etc.) numerical schemes. Other aims are to use a large-eddy simulation (LES) technique to directly predict the near-field aerodynamic noise and to simulate the turbulent flow field with high-fidelity. A three-dimensional parallel LES solver is developed in order to investigate the near acoustic field. Several cases with wide ranges of flow regimes have been computed to validate and verify the accuracy of the method as well as to demonstrate its effectiveness. The time-conservative finite-volume method is efficient and yields high-resolution results with low dissipation similar to higher-order conventional schemes. The time-conservative finite-volume approach offers an accurate way to compute the most relevant frequencies and acoustic modes for aeroacoustic calculations. Its accuracy was checked by solving demonstrative test cases including the prediction of narrowband and broadband cavity acoustics as well as the screech tones and the broadband shock-associated noise of a planar supersonic jet. The second-order time-conservative finite-volume method can solve practically relevant aeroacoustic problems with high-fidelity which is an exception to the conventional second-order schemes commonly regarded as inadequate for computational aeroacoustic (CAA) applications.

Airfoil Aeroacoustics, LES and Acoustic Analogy Predictions

Airfoil Aeroacoustics, LES and Acoustic Analogy Predictions
Author: William Roberto Wolf
Publisher: Stanford University
Total Pages: 238
Release: 2011
Genre:
ISBN:

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.

Aeroacoustics of Low Mach Number Flows

Aeroacoustics of Low Mach Number Flows
Author: Stewart Glegg
Publisher: Academic Press
Total Pages: 554
Release: 2017-02-15
Genre: Science
ISBN: 0128097930

Aeroacoustics of Low Mach Number Flows: Fundamentals, Analysis, and Measurement provides a comprehensive treatment of sound radiation from subsonic flow over moving surfaces, which is the most widespread cause of flow noise in engineering systems. This includes fan noise, rotor noise, wind turbine noise, boundary layer noise, and aircraft noise. Beginning with fluid dynamics, the fundamental equations of aeroacoustics are derived and the key methods of solution are explained, focusing both on the necessary mathematics and physics. Fundamentals of turbulence and turbulent flows, experimental methods and numerous applications are also covered. The book is an ideal source of information on aeroacoustics for researchers and graduate students in engineering, physics, or applied math, as well as for engineers working in this field. Supplementary material for this book is provided by the authors on the website www.aeroacoustics.net. The website provides educational content designed to help students and researchers in understanding some of the principles and applications of aeroacoustics, and includes example problems, data, sample codes, course plans and errata. The website is continuously being reviewed and added to. Explains the key theoretical tools of aeroacoustics, from Lighthill’s analogy to the Ffowcs Williams and Hawkings equation Provides detailed coverage of sound from lifting surfaces, boundary layers, rotating blades, ducted fans and more Presents the fundamentals of sound measurement and aeroacoustic wind tunnel testing

Physics-based Aeroacoustic Modelling of Bluff-bodies

Physics-based Aeroacoustic Modelling of Bluff-bodies
Author: Edward Peers
Publisher:
Total Pages:
Release: 2009
Genre:
ISBN:

In this work physics-based modelling of bluff-body noise was performed with application to landing gear noise prediction. The landing gear is a primary contributor to airframe noise during approach. Noise is primarily generated from the unsteady pressures result- ing from the turbulent flow around various components. The research was initiated in response to the need for an improved understanding of landing gear component noise characteristics and to assist in the development of landing gear noise prediction tools. A computational approach was adopted so that the noise generating physics of the prob- lem could be captured. Governing laws were solved numerically to predict the noise source characteristics and the resulting acoustic far-field. Three-dimensional compress- ible Navier-Stokes simulations were performed to solve the unsteady turbulent near-field flow and the acoustic analogy was used to predict the resulting far-field acoustic pres- sure. The flow solver included a high-order computational aeroacoustics code adopting large-eddy simulation, whilst a Ffowcs Williams and Hawkings solver was used for the acoustic prediction. Circular cylinders in various configurations were selected to rep- resent basic landing gear struts and results were used to form a modelling database. Initially, cylinders at various Reynolds numbers were investigated in cross-flow to de- termine the noise characteristics of a simple model strut. The work was extended to investigate the effect of strut alignment to the flow by simulating cylinders in yaw. The effect of yaw was shown to modify the peak level and frequency of far-field noise spectra. Component interaction effects were then investigated by simulating cylinders in tandem arrangements. The resulting aerodynamic and far-field noise characteristics were shown to be complex and extremely sensitive to the separation distance between the cylin- ders. Finally, a prediction model was developed and validated by comparing predictions against theory and measurements of the noise radiated by a simple two-wheel landing gear model. The results demonstrated the capability of the model to accurately predict correct spectral and directivity characteristics.