Aerodynamic noise from undulated leading edge aerofoils

Abstract

A series of high fidelity numerical simulations are conducted to investigate the noise generated by aerofoils undergoing interaction with vortical disturbances. In particular the focus is on aerofoil leading edge undulations, which have been previously shown to effectively reduce broadband interaction noise. The main objective of this work is to ascertain a comprehensive understanding of the physical mechanisms behind the noise reductions, which to a large extent are still unexplained The simulations are based on the interaction of zero thickness aerofoils with a prescribed spanwise vortex model. The approach is particularly convenient in that it captures non-linear motions, while also maintaining a clean broadband spectra which aids in identifying fundamental trends. The work is split into two main sections, primary leading edge and secondary trailing edge mechanisms. In the first half a number of unique findings are presented concerning the aeroacoustic source mechanisms of the wavy leading edge (WLE). One of the most significant findings is the generation of horseshoe vortex systems which are directly linked to source differences observed at the WLE peak and root. Both source strength reduction and destructive interference mechanisms are investigated in order to determine their contribution towards an increasing noise reduction vs. frequency trend. It is found how the source characteristics over the full surface need to be considered in order to avoid erroneous interpretations of the physics. The findings therefore have important consequences for future approaches concerning which characteristics are crucial for modelling the WLE. In the latter half of the work, the secondary interaction noise sources are investigated in detail. This includes both acoustic backscattering (ABS) and trailing edge vortical scattering (TEVS) effects. Surprising discoveries are made concerning the importance of TEVS at high frequencies, particularly when a WLE is concerned. The TEVS is investigated for both inviscid and viscous flows, and found to be highly dependent on Reynolds number and vortex strength. This highlights an important limitation to WLE performance for implementation purposes, as well as a possible avenue for future research.

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Identifiers

ORCID for Jacob Mansel Turner: orcid.org/0000-0002-0522-4340

ORCID for Jae-Wook Kim: orcid.org/0000-0003-0476-2574

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