Computational Aeroacoustics Of Complex Flows At Low Mach Number
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Aeroacoustics of Low Mach Number Flows
Aeroacoustics of Low Mach Number Flows: Fundamentals, Analysis and Measurement, Second Edition provides a detailed introduction to sound radiation from subsonic flow over moving surfaces. This phenomenon is the most widespread cause of flow noise in engineering systems, including fan noise, rotor noise, wind turbine noise, boundary layer noise, airframe noise and aircraft noise. This fully updated new edition includes additional problems, illustrations and summary materials to support readers. New content covers Rapid Distortion theory (RDT), boundary layer wall pressure fluctuations, and flow induced sound at surfaces. Themes addressing non-compressible flows have also been added, offering coverage of hydroacoustic as well as aeroacoustic applications. New support materials for this edition include course outlines, problem sets, sample MATLAB codes and experimental data to be found at www.aeroacoustics.net. - Addresses, in detail, sound from rotating blades, ducted fans, airframes, boundary layers, and more - Presents theory in such a way that it can be used in computational methods and calculating sound levels - Includes coverage of different experimental approaches to this subject
Computational Aeroacoustics of Complex Flows at Low Mach Number
Designing quiet mechanical systems requires an understanding of the physics of sound generation. Among various sources of noise, aerodynamic sound is the most difficult component to mitigate. In practical applications, aerodynamic sound is generated by complex flow phenomena such as turbulent wakes and boundary layers, separation, and interaction of turbulent flow with irregular solid bodies. In addition, sound waves experience multiple reflections from solid bodies before they propagate to an observer. Prediction of an acoustic field in such configurations requires a general aeroacoustic framework to operate in complex configurations. A general computational aeroacoustics method is developed to evaluate noise generated by low Mach number flow in complex configurations. This method is a hybrid approach which uses Lighthill's acoustic analogy in conjunction with source-data from an incompressible calculation. Flow-generated sound sources are computed by using either direct numerical simulation (DNS) or large eddy simulation (LES); scattering of sound waves are computed using a boundary element method (BEM). In this approach, commonly-made assumptions about the geometry of scattering objects or frequency content of sound are not present, thus it can be applied to a wider range of aeroacoustic problems, where sound is generated by interaction of complex flows with solid surfaces. This new computational technique is applied to a variety of aeroacoustic problems ranging from sound generated by laminar and turbulent vortex shedding from cylinders to realistic configurations such as noise emitted from a rear-view side mirror and a hydrofoil. The purpose of each test case, in addition to validation of the method, is to explore various physical and technical aspects of the problem of sound generation by unsteady flows. Through these test cases, it is demonstrated that the predicted sound field by this technique is accurate in the frequency range in which the sound sources are resolved by the computational mesh. It is also shown that in computation of sound, acoustic analogies are less sensitive to numerical errors than direct computations. Finally, a discussion on the efficacy of LES and the effect of sub-grid scale dynamics on predicted sound is presented.
Computational Aeroacoustics
Author: Jay C. Hardin
language: en
Publisher: Springer Science & Business Media
Release Date: 2012-12-06
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).