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REVIEW bY
Michael S. Howe
Boston University 110 Cummington Mall Boston, MA 02215
book Review
Computational Aeroacoustics: A Wave Number Approach
Author: Christopher K. W. Tam Publisher: Cambridge University Press ISBN: 978-0521806787
Pages: 492 (with 281 illustrations) Binding: Hardcover
Publication Date: September 2012 Price: $125.00
Chris Tam has given in this book a valuable and very pleasing account of how
to resolve the peculiar difficulties encountered in the numerical treatment of aeroacoustics (‘CAA’). The fact that only a tiny fraction (typically 10^-5) of the energy of a mean flow is radiated as sound throws up an array of algorithmic problems that are usually of no significance in traditional computational fluid dynamics (‘CFD')
-- and a naive extension to acoustics of CFD methodology usually leads to grossly ineffective and misleading predictions.
A typical unsteady and noisy flow involves a broad range of frequencies with many different length scales. In CFD unsteady phenomena are often localized, but the acoustic problem involves also small amplitude sound waves that can be well correlated over many hydrodynamic length scales, and perhaps superimposed on an intermediate or larger scale background mean flow through which the sound must propagate to the ‘far field’, frequently over long (many
wavelengths) and sinuous, time dependent paths. This presents a formidable challenge to the numerical analyst who must devise schemes that can resolve propagating short wavelength, high frequency sound waves while taking proper account of damping, wave dispersion and convection by the variable, background flow, and at the same time removing from the weak acoustic signal the
‘numerical noise’ accumulated by the computational scheme. It is also necessary to minimize the spurious dissipation and dispersion caused by the numerical procedure itself. In contrast to most CFD problems, a special ‘non-reflecting’ boundary condition must be imposed at the outer edges of the computational zone to avoid the anomalous ‘numerical’ reflection of sound waves back into the aeroacoustic source region.
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