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FEEG6004 Aeroacoustics

Module Overview

This module covers aerodynamic noise sources and sound propagation in moving media. Aeroacoustics is of great importance in engineering settings involving high speed flows, including transport (aeroplane, aeroengine, automobile, train), industrial processes and the design of consumer devices. For students from acoustical engineering, this module places the discipline of acoustics in the wider context of fluid mechanics. For students with a background in aerodynamics, this module provides a self-contained introduction to acoustics and its interactions with other aspects of fluid mechanics.

Aims and Objectives

Module Aims

This module introduces the fundamental physical principles of aero-acoustics as well as some modelling techniques. The aim is to provide students with sufficient background knowledge to embark on an industrial career or further study in aeroacoustics or including elements of aeroacoustics.

Learning Outcomes

Knowledge and Understanding

Having successfully completed this module, you will be able to demonstrate knowledge and understanding of:

  • Discuss the generation and propagation of sound in fluids
  • Explain the principle of the Lighthill acoustic analogy, and how this is related to sound generated by turbulent flows
  • Explain how scaling laws may be derived (for some simple examples), and to interpret these.
  • Explain how mean flow and boundaries can affect sound generation and propagation.
  • Apply aeroacoustics theory to new problems.
  • Understanding of some of the current state-of-the-art research in aeroacoustics.
Transferable and Generic Skills

Having successfully completed this module you will be able to:

  • Write computer programs and reports.
  • Apply critical analysis and evaluation skills.
  • Ability to read, understand and interpret scientific papers.
  • Synthesise information from a range of sources.
  • Communicate clearly in written reports.
Subject Specific Practical Skills

Having successfully completed this module you will be able to:

  • Recognize and define terms specific to aeroacoustics.
  • Use relevant mathematical methods to solve problems in aeroacoustics.
  • Synthesise theory from different fields of study (eg. fluid dynamics, acoustics, mathematical methods).
  • Model some complex noise generation problems.
  • Appreciate the limitations of different modelling techniques,
Cognitive Skills

Having successfully completed this module you will be able to:

  • Analyse aeroacoustics problems and select appropriate methods for solution of the problems.
  • Assess whether the complexity of a problem in aeroacoustics may be reduced, e.g. by the use of scaling laws.
  • Improved ability to read and interpret scientific textbooks and papers related to aeroacoustics.

Syllabus

- Brief review of fluid mechanics: conservation laws, thermodynamics, vortex dynamics. - Propagation of linear waves in moving media: linearized Euler equations, acoustics, vortical and entropy waves, the convected wave equation, basic properties of sound waves in moving media, sound refraction by non-uniform flows. - Acoustic impedance with flow: definition and properties of acoustic impedance, Helmholtz resonator, Ingard and Myers conditions for impedance with flow. - Methods for solving the wave equations: Green’s functions, Green’s formula, far field approximations, compact sources, and interferences. - Noise radiation by simple sources: types of sources, effect of source motion, convective amplification, the Doppler effect. - Sound radiation by free shear flows: Lighthill’s analogy, application to noise from turbulence. - Noise radiation from solid surfaces: general theory of Ffowcs Williams Hawkings and application to wave extrapolation. - Rotor noise: description of source mechanisms from aerofoils, - Duct acoustics: sound field in ducts and wave guides, properties of duct modes. - Turbo-machinery noise: fan rotor-alone tones, interaction tones, buzz-saw noise. - Aeolian tones: cavity noise, flow-acoustic feedback loops.

Learning and Teaching

Teaching and learning methods

Teaching methods include Three sessions per week which will be used to present the theory and worked examples. (Lecture notes will be available in electronic format.) Tutorial classes to discuss exercises sheets and worked examples will also be provided. Learning activities include - Private study: students are expected to consult relevant textbooks and research papers, in order to further research the information and theory explained during lectures. - Problems sheets will be provided which contain exercises similar to the worked examples presented during the lectures. These will be backed up (as required) by problems classes. Solutions to the exercises will be provided. - Some of the exercises will involve simple computer programming to apply aeroacoustics theory to a sample problem, to investigate the underlying physics, and to explore the limitations of various modelling methods. - The coursework assignments provide an opportunity to apply some of the aeroacoustics theory presented in the lectures to a more substantial problem. This is likely to require some simple computer programming, and further reading, in addition to using the material provided during the lectures. - Revision lectures at the end of the course should provide additional time to discuss typical examples of exam questions.

TypeHours
Independent Study114
Lecture36
Total study time150

Resources & Reading list

A.D. Pierce (1989). Acoustics. 

M.S. Howe (2002). Theory of Vortex Sound. 

M.E. Goldstein (1976). Aeroacoustics. 

D.G. Crighton et al. Springer-Verlag (1992). Modern methods in analytical acoustics. 

Assessment

Summative

MethodPercentage contribution
Coursework 15%
Coursework 15%
Examination  (120 minutes) 70%

Referral

MethodPercentage contribution
Examination 100%

Repeat Information

Repeat type: Internal & External

Linked modules

Prerequisites: FEEG2003 Fluid Mechanics or SESA2022 Aerodynamics.

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