2 PhD Studentships in Aeroacoustics
Department of Engineering
Vacancy Reference No: NA07937

Applications are invited for two PhD studentships that are a part of a new collaboration between Dyson Ltd and the Department of Engineering at Cambridge. The studentships are to investigate air movement for high efficiency and low noise in the power range used for domestic applications. The projects involve a study of unsteady fluid mechanics, flow instability and acoustics and each have an experimental and a model component. This is a unique opportunity to address a real design challenge with a leading company through original research, which will have wider impacts on the acoustic emissions of many other sub 1kW air moving machines.

The studentships are to commence in October 2011.

Project 1: Towards a Silent Fan
The Dyson Air Multiplier’s striking design offers many advantages in operation: the airflow it generates is free of the turbulence associated with conventional fans; it is efficient, easy to clean and as quiet as other fans. The aim of this project is to take the design even further and create the ultimate low-noise fan while staying within a strict design envelope. The cooling airflow involves no moving blades and is at a low enough speed that the noise from this flow is not significant. This means that the focus of the project will be on novel, quiet internal flow components. Components of interest will be: the impeller blades that produce tonal noise, which is enhanced by interactions with the inlet and outlet geometry; and sections of the flow path with abrupt curvature that can cause local separations, wakes and noise. In this project we will develop simplified models to predict noise generated from the individual components (impeller, guide vanes, air jet, etc) and their interaction and integrate these ideas to develop design rules for reducing noise. The project aims to determine the lowest noise level that can be achieved for a fan with given air flow-rate, air speed and efficiency, and to develop design concepts that can achieve it.

Project 2: Aeroacoustics of Cyclone Separators
Cyclones are complex three-dimensional flows that swirl about a central column of fluid inline with the axis of rotation. The column consists of a solid-body rotation that at low flow speeds do not show large instabilities. However as the flow speed increases, the vortex core deforms into a rotating spiral and begins to precess around the central axis. The instability leads to a temporally periodic motion that results in a tonal noise. It is suspected that the frequency of the processing vortex core has a relationship with the frequency of the observed sound.

The main objectives of the project are to develop a model for the precessing vortex core and to discover ways of controlling noise either by suppressing the periodic flow instability passively, actively or by applying anti-sound control¬.

The challenge is to stabilise the flow or reduce the noise without introducing a loss in performance either in the form of pressure drop or particle separation.

The solution could have a wide range of applicability from vacuum cleaners to helicopter intakes and Ranque-Hilsch vortex tubes used for refrigeration.

Eligibility
The application is open to nationals of any country, but full tuition fees are not covered for overseas (non-EU) students. Stipends for 2010-2011 are 13,290 GBP, and available for 3 years. Candidates should hold an undergraduate degree in aerospace, mechanical or acoustical engineering, physics or related fields.

The projects would involve a mix of experiments in anechoic chambers, wind and water tunnels, theoretical modelling and numerical simulations. The student will be supervised by Dr. Anurag Agarwal and Professor Dame Ann Dowling and would work closely with researchers and designers at Dyson’s head quarters. The studentship is available from October 2011, though an earlier start date might be possible. Applications should include a CV, contact details for two professional referees, and should be sent to Dr. Anurag Agarwal, Engineering Department, Trumpington Street, Cambridge CB2 1PZ (email: aa406@cam.ac.uk). Informal enquiries can be made to Dr. Anurag Agarwal.

Application review will begin March 1, 2011 and will continue until the positions are filled.
Limit of tenure applies 3 years
Closing date: 6 May 2011.

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