Aerodynamic and Aeroacoustic characterisation of tip leakage flows

Despite more than fifty years of research into fan noise, the mechanism and understanding of the noise generated at the blade tip is still poorly understood. This is mainly because there are likely to be a number of different source mechanisms and also because the unsteady flow, and hence the sources of noise, are confined to the very small regions around the blade tip. This project outlines an integrated, predominantly experimental work aimed at understanding, quantifying and characterising more fully the mechanisms of the noise generated at the tip of a ducted fan.
To gain a detailed understanding of the flow in the vicinity of the aerofoil tip, detailed flow and unsteady surface pressure measurements will be performed on a single, non-rotating aerofoil located close to a rigid wall in an open jet wind tunnel. The design of the rig, which represents one of the most challenging aspects of the project is key to fully understanding these subtle and complex flow features. Several complementary flow velocity measurement techniques (HWA, LDA, PIV) will be employed to fully characterise the steady and unsteady flow near the blade tip. Combining this flow and acoustic data provides a fundamental understanding into the noise generating mechanisms associated with tip leakage noise, which provides the bases for developing noise mitigation measures.