Book Review: Aeroacoustics of Low Mach Number Flows: Fundamentals,Analysis and Measurement

Reviewed by: Seongkyu Lee, Department of Mechanical and Aerospace Engineering, University of California, Davis, CA, USA

“Aeroacoustics of Low Mach Number Flows, 2nd Edition,” authored by Stewart Glegg and William Devenport, is an authoritative and comprehensive book, serving as an essential resource for students and professionals in the field of aeroacoustics. The book meticulously covers fundamentals, analysis, and measurement techniques relevant to low Mach number flows. The authors balance theoretical depth with practical application, making this book both intellectually stimulating and practically useful.

The book is methodically organized into seven parts, starting with the fundamentals of aeroacoustics and advancing through complex mathematical methods and practical applications. This logical progression not only makes it a valuable reference but also a suitable textbook for graduate-level courses. In particular, a summary of key results and the problems at the end of each chapter are thoughtfully designed to reinforce learning and stimulate further exploration, proving useful for instructors and students.

Part One – Fundamentals, consists of three chapters. These initial chapters provide a solid foundation, discussing the basic equations of unsteady fluid dynamics and linear acoustics, essential for newcomers to understand the more complex topics in later chapters. Chapter 3, in particular, delves into mathematical methods used in aeroacoustic analysis, discussing wave equations, integral solutions, and Green’s functions in detail. It is notable that the second edition features numerous new illustrative figures, visually displaying complex concepts.

Part Two – Foundations of Aeroacoustics, also comprising three chapters, delves into the core of aeroacoustics. It explores foundational equations such as Lighthill’s acoustic analogy for flow-induced noise in an unbounded domain, Curle’s theorem for the inclusion of stationary surface sources, and the Ffowcs Williams and Hawkings equation for arbitrary moving sources. The authors introduce the sound generation mechanisms of open rotors and propellers, combining theoretical analysis with real-world applications and discussing recent research findings, including blade-vortex interaction noise and analyses for rotor noise. Both time-domain and frequency-domain analyses for rotor noise are derived and discussed.

Part Three – Unsteady Blade Loading, with three chapters, presents unsteady fluid dynamics necessary for estimating surface loading, a crucial part of aeroacoustic noise sources. It discusses Amiet’s approach, the solution of Sears problem, Goldstein’s approach for flows with distortion or Rapid Distortion Theory, and Howe’s and Powell’s vortex sound theories.

Part Four – Turbulent Flows, includes three chapters about the basic mathematical and statistical approaches for analyzing flow turbulence in relation to aeroacoustics. It covers the expected value, auto- and cross-correlation functions in both temporal and spatial domains, and auto- and cross-spectrum, and wall pressure spectrum. These concepts and tools are particularly useful for understanding the later chapters on broadband noise that is generated by flow turbulence.

Part Five – Broadband Flow Noise from Surface Interactions and Fans, consisting of four chapters, addresses the complex dynamics of sound generation in turbulent flows, such as leading-edge noise, trailing-edge noise, and roughness noise, as well as duct acoustics and fan noise. The authors explore the mechanisms of turbulence-generated sound with mathematical models and experimental data, providing not just predictive approaches but also valuable insights for noise reduction in aeroacoustic applications.

Part Six - Experimental Methods, consisting of three chapters, is dedicated to experimental techniques in aeroacoustics. This section is particularly noteworthy for its practical orientation, discussing the use of microphones, flow measurement devices, and wind tunnel testing methods. This part is invaluable for practitioners in the field, offering guidance on the implementation of experimental setups and the interpretation of data.

Part Seven – Advanced Mathematical Methods, provides further mathematical details and approaches about edge scattering, with practical applications in leading-edge and trailing-edge noise.

What sets this edition apart is its clear and accessible language, making complex concepts understandable even for those with limited fluid dynamics and acoustics background. The book discusses not only theories but also practical applications and real-world examples, including aircraft fan noise, open propeller noise, and rotor noise, which are crucial for engineers and researchers. This book truly reflects the depth and breadth of the authors’ knowledge in the complex discipline of aeroacoustics.

The inclusion of the latest research and developments in various chapters makes this book particularly valuable. The authors have integrated new findings and methodologies, ensuring the book’s relevance in the rapidly evolving field. The emphasis on experimental techniques is commendable, providing invaluable insights for experimental aeroacoustics research.

In conclusion, “Aeroacoustics of Low Mach Number Flows, 2nd Edition” is an indispensable resource for anyone interested in aeroacoustics, offering invaluable knowledge and insights into the world of low Mach number aeroacoustics for graduate students, academic researchers, and professional engineers.