Aerodynamic and aeroacoustics characterisation of tip leakage flow

Abstract

Among the various noise sources related to ducted fans, the noise generated by the interaction of tip leakage flow with the blade’s geometric singularities is one of the least understood. This thesis deals with identifying the mechanisms involved in the generation and reduction of tip leakage noise for a single stationary aerofoil, which enables a detailed analysis of this specific noise source. Through a combination of experimental, parametric, and numerical investigations, this research explores the fluid dynamic instabilities responsible for the noise sources, the key parameters influencing these sources, and the effectiveness of noise-reducing treatments. Two dipole-type noise sources were identified and attributed to fluid-dynamic instabilities occurring in the tip-gap region: roll-up and shedding of vortical structures generated during the separation of the flow at the pressure side tip edge. The key non-dimensional parameters influencing these noise sources include the geometric angle of attack, the ratio of maximum aerofoil thickness to gap size, and the ratio of gap size to boundary layer thickness of the bottom wall. This investigation also examines the impact of treatments such as porous material and rounded pressure side tip edge, with both treatments leading to significant noise reductions. Finally, numerical simulations provide a definitive understanding of the tip leakage flow, confirming the presence of instabilities also for the configuration with a rounded pressure side tip.

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Identifiers

ORCID for Ivan Saraceno: orcid.org/0000-0003-1193-8427

ORCID for Bharath Ganapathisubramani: orcid.org/0000-0001-9817-0486

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