An extension to Hanson’s theory of harmonic noise of rotors

The rapid emergence of electric-vertical-take-off-and-landing (eVTOL) aircraft has renewed interest in rotor-generated noise. Because eVTOL configurations rely on many simultaneously operating propellers, accurate prediction demands higher-fidelity aeroacoustic tools than those used for conventional single-rotor systems. This study extends Hanson’s frequency-domain harmonic-noise formulation by coupling it with advanced aerodynamic models that resolve the blade-loading distribution more realistically. Point and line load compactness are addressed with an extended QPROP model for axial inflow propellers and using prescribed vortex wake and free vortex wake methods for non-axial inflow propellers, which furnishes the unsteady sectional forces for propellers at arbitrary pitch angles. Planar (chord-wise) loading is captured using an airfoil panel method. A novel viscous vortex panel method is developed that does not rely on a global Newton solver to obtain a flow solution around an airfoil. This method has the drawback of not being able to obtain self-consistent solutions, but the convergence issues at high angles of attack for airfoils experienced in other viscous vortex panel methods like XFOIL are avoided. The resulting time histories are transformed via discrete Fourier analysis to supply the modal loading inputs required by Hanson’s equations. Predictions obtained with these refined load models are benchmarked against (i) experimental data for both axial and non-axial inflow rotors and (ii) time domain numerical solutions for axial inflow propellers. The comparison demonstrates a significant improvement in noise-level accuracy across harmonic orders.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Nanjappa, Niranjan

Contributors dc:contributor

• Clarke, Matthew

• Aeroacoustics
• Aerodynamics

Statement dc:rights

• Copyright, 2025 Niranjan Nanjappa

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129794

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129794