Investigation of Wake Dynamics of a Slender Symmetric Trailing Edge Hydrofoil

TL;DR

This work tackles wake dynamics behind a slender symmetric hydrofoil at zero angle of attack by integrating high-resolution Large Eddy Simulation (LES), time-resolved Particle Image Velocimetry (PIV), and Proper Orthogonal Decomposition (POD). The experimental data, collected in a closed-loop square channel, are directly compared to a scale-resolving CFD pipeline that advances from steady SST-RANS through SAS to LES on a ~5×10^8-node mesh, capturing near-wall and wake structures at Reynolds numbers up to $Re^*\approx 2.24\times10^6$. POD reveals a broadband yet structured wake, with mode 1 representing the primary von Kármán wake and higher modes forming coupled pairs around $f\approx$ a few hundred hertz; the dominant spectral peak from PIV (~$f\approx295$ Hz) aligns with the LES and POD findings near $f\approx312$–$318$ Hz. The study provides a validated, high-fidelity dataset and demonstrates that LES can reliably reproduce wake dynamics and spectral features critical for vibration mitigation and design of hydrofoil-based hydraulic components.

Abstract

Accurate prediction of wake dynamics behind hydrofoils is critical for mitigating vortex-induced vibrations and improving the performance of hydraulic machinery. Conventional turbulence modeling approaches often struggle to capture the unsteady, coherent structures governing wake behavior, particularly for slender hydrofoils operating at high Reynolds numbers. This study addresses this limitation by combining scale-resolving numerical simulations, including high-resolution Large Eddy Simulation (LES), with Particle Image Velocimetry (PIV) measurements to investigate the turbulent wake of a symmetric, blunt trailing-edge hydrofoil operating at zero angle of attack. The flow was analyzed at a Reynolds number of approximately 7.5x10e5, i.e. close to the onset of wake-structure interaction effects. LES was performed using a fine mesh of approximately 500 million nodes to resolve near-wall and wake dynamics beyond the experimental field of view, while PIV measurements provided time-resolved velocity fields downstream of the trailing edge. Proper Orthogonal Decomposition (POD) was applied to the PIV data to extract dominant coherent structures and quantify their contribution to the turbulent kinetic energy. POD analysis reveals that energy is distributed across many modes, with the leading mode capturing the primary wake dynamics and higher modes forming coupled oscillatory pairs associated with von Karman vortex shedding. PIV-LES agreement shows that central wake measurements combined with numerical simulations enables full wake reconstruction and validates modeling for vibration-relevant hydrofoil dynamics.

Figures (42)

• Figure 1: Schematic view of the velocity measurement using PIV technique.
• Figure 2: View of test section (above) and section view (below) with PIV FOV in red. The frontal and top opening gave optical access to camera and laser sheet respectively.
• Figure 3: Velocity profile locations downstream of the hydrofoil. The profile lines $p_1$, $p_2$, $p_3$, $p_4$, $p_5$, $p_6$, $p_7$, correspond to the chord length of 0%, 2%, 4%, 6%, 10%, 14% and 22%, respectively. In red the area investigated by the PIV.
• Figure 4: Isometric view of the hydrofoil. All dimensions are in mm.
• Figure 5: Hexahedral mesh around hydrofoil (x-scale = 0.05 m).