Scattering by porous aerofoil adaptations

Machines, and aircraft, in particular, can generate a large amount of noise that causes disruption and irritation. From the beginning of the jet era, the need to control aeroacoustic noise generation has been important in order to minimise the environmental impact of the aviation industry and its expansion. Sharp rigid edges are known to efficiently scatter sound from an incoming unsteady flow. They form an important source of airframe noise from the leading and trailing edges of aerofoils, as well as contributing to turbo-machinery noise through fan blades and guide vanes. The study of owl flight has led to numerous bio-inspired adaptations designed to reduce aerodynamic noise passively. Firstly, through material changes: porosity, elasticity, and surface treatments; secondly, through geometric or structural changes: serrations, slits, finlets, and canopies. Each has been shown to have the potential to achieve significant reductions in far-field sound. However, it remains unclear precisely how these reductions are achieved for a number of these designs, hindering robust application. In this thesis, we consider the effect on scattering of porous adaptations to aerofoils. Since any material adaptation will have a finite extent, it is interesting to understand interference effects between scattered fields arising from the additional material junctions. This can be achieved by solving certain matrix Wiener—Hopf problems. To do this, we present an effective numerical implementation of a previously proposed iterative method. We also derive a singular integral equation amenable to direct solution by a spectrally accurate method. This approach enables yet another solution for scattering by a rigid flat plate of finite chord. It further allows the investigation of a range of scattering problems relevant to porous adaptations, including the modelling of porosity in the context of edge scattering. It facilitates theoretical models of a porous leading edge of finite extent, and of a slot a finite distance downstream of a leading edge. To conclude this work, we consider the effect of a porous canopy structure on the incident disturbances that act as source terms for edge scattering problems. Although the solutions in this thesis are applied to porosity in aeroacoustics, the numerical Wiener—Hopf approach used may have broader application in wave scattering and beyond.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Priddin, Matthew

Advisor dc:contributor.advisor

• Ayton, Lorna

• Aeroacoustics

Licence

• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0000-0001-7223-0567

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/343788