Monograph on sound generation by turbulence and surfaces in arbitrary motion, discussing sound and multipole fields and governing equations

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Sound Generation by Turbulence and Surfaces in Arbitrary Motion

The presence of the edge of a half plane in a turbulent fluid results in a large increase in the noise generated by that fluid at low Mach numbers. The parameter which is important is the product then the farfield sound has the same features as would be predicted by geometrical acoustics. The edge does not produce any significant sound amplification.

Aerodynamic sound generation by turbulent flow in the vicinity of a scattering half plane

Acoustic radiation from an airfoil in a turbulent stream

Noise due to turbulent flow past a trailing edge

Preface Acknowledgements Introductory comments 1. Mechanical vibrations: a review of some fundamentals 2. Sound waves: a review of some fundamentals 3. Interactions between sound waves and solid structures 4. Noise and vibration measurement and control procedures 5. The analysis of noise and vibration signals 6. Statistical energy analysis of noise and vibration 7. Pipe flow noise and vibration: a case study 8. Noise and vibration as a diagnostic tool 9. Worked examples Appendices Problems Answers to problems Index.

Fundamentals of noise and vibration analysis for engineers

An extension is made to Lighthill's general theory of aerodynamic sound, so as to incorporate the influence of solid boundaries upon the sound field. This influence is twofold, namely (i) reflexion and diffraction of the sound waves at the solid boundaries, and (ii) a resultant dipole field at the solid boundaries which are the limits of Lighthill's quadrupole distribution. It is shown that these effects are exactly equivalent to a distribution of dipoles, each representing the force with which unit area of solid boundary acts upon the fluid. A dimensional analysis shows that the intensity of the sound generated by the dipoles should at large distances x be of the general form I$\propto $ $\rho \_{0}$ U$\_{0}^{6}$a$\_{0}^{-3}$ L$^{2}$x$^{-2}$, where U$\_{0}$ is a typical velocity of the flow, L is a typical length of the body, a$\_{0}$ is the velocity of sound in fluid at rest and $\rho \_{0}$ is the density of the fluid at rest. Accordingly, these dipoles should be more efficient generators of sound than the quadrupoles of Lighthill's theory if the Mach number is small enough. It is shown that the fundamental frequency of the dipole sound is one half of the frequency of the quadrupole sound.

N. Curle

Papers

The Influence of Solid Boundaries upon Aerodynamic Sound