Aeroacoustics

Learning Outcomes

Transferable and Generic Skills

Having successfully completed this module you will be able to:

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

Knowledge and Understanding

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

• Explain how mean flow and boundaries can affect sound generation and propagation.
• Understanding of some of the current state-of-the-art research in aeroacoustics.
• Apply aeroacoustics theory to new problems.
• 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.
• Discuss the generation and propagation of sound in fluids

Subject Specific Practical Skills

Having successfully completed this module you will be able to:

• Appreciate the limitations of different modelling techniques,
• 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.
• Recognize and define terms specific to aeroacoustics.

Cognitive Skills

Having successfully completed this module you will be able to:

• 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.
• Analyse aeroacoustics problems and select appropriate methods for solution of the problems.

Full CEng Programme Level Learning Outcomes

Having successfully completed this module you will be able to:

• The material in this course is rarely found in undergraduate courses and is similar in level to our Advanced Course in Aeroacoustics we provide for industry practitioners. The two coursework assignments require the students to successfully apply the knowledge they have learned in the lectures. Both require the student to address the physical principles underlying the equations in addition selecting and applying relevant mathematical equations. At least one includes a section on making engineering judgments based on the maths/physics analysis.
• The course does not include purely numerical models, but does include a wide range of analytical and semi-analytical (i.e. analytical methods requiring numerical solution) methods for noise modelling. Both coursework assignments require the students to successfully apply these techniques to specific problems. The limitations of the methods are discussed in lectures, touched on in the assignment, but assessed primarily through the viva at the end of course.

Partial CEng Programme Level Learning Outcomes

Having successfully completed this module you will be able to:

• The course is designed to keep engineering, maths and phsyics understanding in step. The communication of the underlying physical principles is assessed in the assignments which require a qualitative description of the results in addition to calculations. It is also assessed in the discussion section of the viva, which includes a verbal description of the results of one of the courseworks and a free discussion on an advance to the coursework itself that the candidate has not seen before.

• 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.

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.

Summative

This is how we’ll formally assess what you have learned in this module.

Referral

This is how we’ll assess you if you don’t meet the criteria to pass this module.

Repeat

An internal repeat is where you take all of your modules again, including any you passed. An external repeat is where you only re-take the modules you failed.