Spatio-temporal localization of canonical dynamic stall flow scales across varying Reynolds numbers

Dynamic stall is a well-known phenomenon in rotary wing flows, leading initially to an overshoot in lift performance followed by a rapid loss in such performance. During the dynamic stall process, the flow over a lifting surface becomes unsteady and evolve into a flow dominated by large-scale vortex structures. The emergence and evolution of these vortex flow structures contribute to large variations in loading, thus affecting both the aerodynamic performance and the structural integrity of aircrafts. Previous studies on airfoils have identified some of the underlying flow features and have revealed dominant frequencies linked to the formation of the leading-edge vortex. However, the lack of precise spatial localization of dominant wavenumber scales and frequencies limits the implementation of effective flow control methods. The present work focuses on the dynamic stall flow features leading up to the development of the dynamic stall vortex at chord-based Reynolds numbers, Rec, between 10,000 and 500,000 using time-resolved PIV data acquired for a dynamically pitching NACA 0012 airfoil at a reduced frequency of 0.05. A novel scale analysis technique combining the use of log-Gabor filters and Riesz-transforms was applied to the 2-D PIV velocity fields to provide a better localization and a multiscale, multi-orientation quantification of the wavenumber amplitudes associated with the dominant flow features. In general, the amplitudes associated with these wavenumbers were observed to reach an amplified state during the initial breakdown of flow structures within the shear layer at a different stage of the pitch cycle depending on the Reynolds number.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Awate, Vanessa

Contributors dc:contributor

• Ansell, Phillip J.
• Ansell, Phillip J
• Gupta, Rohit
• Dutton, Craig
• Saxton-Fox, Theresa
• Chamorro Chavez, Leonardo P.

• Dynamic Stall
• Naca 0012
• Particle Image Velocimetry
• Wavenumber Spectra
• Log-gabor Filter
• Riesz Transform
• Trailing-edge Separation
• Leading-edge Stall
• Unsteady Flows
• Shear Layer Separation
• Vortex-dominated Flows
• Transitional Reynolds Number

Statement dc:rights

• Copyright 2025, Vanessa Awate

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/130099

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F130099