Dynamical features of the wake behind a pitching foil

Area of Science:

• Fluid dynamics
• Hydrodynamics
• Aerodynamics

Background:

• Previous research explored the three-dimensional wake transition behind a pitching foil.
• Understanding wake dynamics is crucial for applications in marine engineering and bio-inspired propulsion.

Purpose of the Study:

• To create a comprehensive phase space map of wake dynamics based on pitching frequency and amplitude.
• To identify and characterize key dynamical transitions in the wake structure.
• To investigate the relationship between wake deflection and the transition to three-dimensional flow.

Main Methods:

• Numerical simulations were conducted at a fixed Reynolds number (Re=1700).
• Pitching frequency and amplitude were systematically varied to explore the phase space.
• Three-dimensional direct numerical simulations (DNSs) were employed to validate findings.

Main Results:

• Identified transitions include Bénard-von Kármán (BvK) to reverse BvK vortex streets, wake deflection, and 2D to 3D wake transitions.
• The 2D to 3D transition boundary is located beyond the wake deflection boundary, indicating a sequential occurrence.
• Confirmed the physical realizability of short wavelength modes and found good agreement between DNS and Floquet mode reconstructions.

Conclusions:

• The study provides a detailed map of wake transitions, supporting previous two-dimensional assumptions at lower Reynolds numbers.
• Wake deflection is a precursor to the three-dimensional transition.
• The research validates the existence of streamwise structures in the wake through advanced simulation techniques.