Investigation of the noise generating mechanisms related to the tip leakage flow

What is it about?

Tip leakage noise is generated by the interaction between the blade tip singularities and the tip leakage flow. The latter is a 3D-unsteady-flow that occurs in the clearance through a blade tip and a duct wall. It is produced by the relative motion between the blade tip and the casing wall as well as by the pressure difference between the Suction Side and the Pressure Side of a blade.

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Photo by Luka Slapnicar on Unsplash

Photo by Luka Slapnicar on Unsplash

Why is it important?

Past investigations on a single-fixed aerofoil, located in a open jet wind tunnel, have highlighted the presence of two humps in the pressure measurements, at low and high frequencies respectively. The first one is probably linked to a separation of the tip leakage flow that occurs at the pressure side tip edge. Such a separated flow generates small turbulent eddies responsible on the other hand of the second noise hump. The present study proves experimentally the relationship between the first hump and the separated flow. This result is achieved applying a conditional averaging technique and the Proper Orthogonal Decomposition (POD) to the flow field. The second hump is connected with the strong gap flow located around the midchord. The generating mechanism remains still unclear.