Hydrodynamics of wake interactions for oscillating foils in simple schools

• Author / Creator

  Gungor, Ahmet

• Hydrodynamics of the flow around multi-foil systems, representing the tailfin dynamics of collectively
  swimming fish or fish schooling, were investigated by directly solving the Navier-Stokes
  equations across a range of flow conditions. The wake and performance of the pitching foils in
  schooling configurations are examined across a broad parameter space, including Reynolds number,
  Strouhal number, pitching amplitude, phase difference, and foil spacing. The aim of this
  study is to enhance our understanding of the fluid dynamics associated with fish-like swimmers
  in schooling configurations. The insights gained are intended to inform the design of advanced
  man-made propulsors, operating in schooling configurations.
  The dynamics of unsteady interactions behind schooling foils were explored at a Reynolds
  number of 1000-12000, unveiling their correlation with performance metrics. At lower Strouhal
  numbers, quasi-steady performance characteristics were observed, aligning with the persistence
  of wake symmetry. Conversely, higher Strouhal numbers exhibited unsteady interactions between
  vortex streets in the wake behind the foils, leading to intricate transitional behaviors. Specifically,
  asymmetric vortex streets produced by in-phase pitching foils merged into a symmetric
  wake, while out-of-phase pitching foils experienced a transition from symmetric to asymmetric
  wakes. Further analysis of vortex circulation indicated that secondary structures that separate from
  the lower wake influenced the primary structures of the upper wake, initiating the wake merging
  process. Wake patterns were categorized by their merged-separated and steady-transient features,
  prompting the development of a novel mathematical model to differentiate between merged and
  separated patterns. Additionally, novel scaling laws were formulated to estimate the steady performance
  metrics of the foils under varying flow conditions, resulting in two sets of scaling equations
  grounded in empirical and physics-based methodologies. The study also delved into the threedimensional
  instability characteristics of parallel pitching foils in the turbulent regime. A unique
  spanwise instability within the separating shear layer, resulting from the proximity of one foil to
  another, was identified, and a mechanism responsible for the suppression of spanwise instabilities
  on leading edge vortices under extreme foil proximity effect was elucidated.

• Subjects / Keywords

  • Vortex dynamics
  • Wake interactions
  • Oscillating foils
  • Schooling configurations
  • Computational fluid dynamics (CFD)

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-hndd-nk31

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.