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FEEG6004 Aeroacoustics

Module Overview

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. This module covers aerodynamic noise sources and sound propagation in moving media.

Aims and Objectives

Module Aims

To introduce the fundamental physical principles of aeroacoustics as well as some modelling techniques.

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.
Cognitive Skills

Having successfully completed this module you will be able to:

  • Recognize “aeroacoustics” problems.
  • 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.
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.
  • Link theory related to fluid dynamics and acoustics.
  • Synthesise theory from different fields of study (eg. fluid dynamics, acoustics, mathematical methods).
  • Model complex noise generation problems.
  • Appreciate the difficulties associated with modelling aeroacoustic problems.

Syllabus

- Brief review of fluid mechanics: conservation laws, thermodynamics, vortex dynamics. - Propagation of linear waves in moving media: linearized Euler equations, acoustics, vertical and entropy waves, the convected wave equation, basic properties of sound waves in moving media, sound refraction by non-uniform flows, geometrical acoustics. - Acoustic impedance with flow: definition and properties of acoustic impedance, Helmholtz resonator, Ingard and Myers conditions for impedance with flow. - Acoustic energy and intensity: properties of conservation of acoustic energy, acoustic intensity and power, generalization to moving media. - 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, ‘wavy wall’ problems, wave packets. - Sound radiation by free shear flows: Lighthill’s analogy, application to noise from turbulence, vortex sound theory. - 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.

Special Features

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Learning and Teaching

Teaching and learning methods

Teaching methods include Three lectures 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. Also, solutions to the exercises will be provided. - Revision lectures at the end of the course should provide additional time to discuss typical examples of exam questions. - Coursework assignments will require the students to apply some of the aeroacoustics theory presented in the lectures to a practical problem. This is likely to require some simple computer programming, and further reading, in addition to using the material provided during the lectures.

TypeHours
Independent Study114
Lecture36
Total study time150

Resources & Reading list

A.D. Pierce (1989). Acoustics. 

M.E. Goldstein (1976). Aeroacoustics. 

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

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

Assessment

Assessment Strategy

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Summative

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

Referral

MethodPercentage contribution
Exam 100%

Repeat Information

Repeat type: Internal & External

Linked modules

Prerequisites: FEEG2003 Fluid Mechanics or SESA2022 Aerodynamics.

Pre-requisites

To study this module, you will need to have studied the following module(s):

CodeModule
SESA2022Aerodynamics
FEEG2003Fluid Mechanics
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