The aim of this project is to investigate air movement for high efficiency and low noise in the power range used for domestic applications in collaboration with Dyson. The project involves a study of unsteady fluid mechanics, and acoustics and has an experimental and a model component.
The Dyson air multiplier provides the ideal external flow to be the basis of a silent fan. The cooling air flow is steady and at a low enough speed that the noise of this flow entraining and mixing with the surrounding air will not be significant.
Having a quietened external air stream emphasises the noise of the internal components which is still noticeable within a quiet office or domestic environment. There are several sources of noise from the internal flow passages. The impeller blades produce tonal noise which is enhanced by interactions with the inlet and outlet. Any wakes from upstream bodies interact with the moving components of the impeller and are also a source of noise. Similarly, sections of the flow path with abrupt curvature can cause local separations, wakes and noise. The most elegant design for low noise would aim to reduce noise at source. Where some aspects of noise generation are inherent in the design, noise absorbent material could be used for subsequent attenuation.
The task is made more difficult because of performance and design constraints. In this project we use the air multiplier as a test case for a fan optimised for low noise.