<p>Tip vortices generated at the tip of lifting surfaces pose significant challenges in fluid dynamics, causing induced drag, noise, and cavitation erosion risk across aerospace and hydraulic applications. Among the various mitigation strategies, porous tips have been explored with mixed results, showing limited effectiveness in diffusing concentrated vorticity. In this study, we introduce a gyroid-based porous tip as a novel passive flow control device for tip vortex mitigation. A gyroid is a triply periodic minimal surface that forms a smooth and tortuous porous 3D network. A gyroid-based porous insert was attached to an elliptical NACA 16-020 hydrofoil tip (Re ≈ 9 × 10<sup>5</sup>), replacing 3%, 5%, and 9% of the span. Laser Doppler Velocimetry (LDV) measurements revealed that increasing the gyroid portion dramatically reduces maximum tangential velocity while enlarging the vortex core radius. The vortex circulation remains unchanged, indicating a diffusion mechanism that spreads concentrated vorticity over a larger core. At 12° incidence, the 9% gyroid insert reduced peak tangential velocity by a factor of 3.2 alongside a sixfold increase in vortex core radius. Consequently, the minimum pressure coefficient at the vortex center increased from <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$-1.4$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>-</mo> <mn>1.4</mn> </mrow> </math></EquationSource> </InlineEquation> to <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$-0.1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>-</mo> <mn>0.1</mn> </mrow> </math></EquationSource> </InlineEquation>, reducing significantly the risk of cavitation. Flow visualization confirmed complete suppression of tip vortex cavitation across all tested conditions. The gyroid effectiveness was verified for both tripped and natural boundary layer transitions. Critically, hydrodynamic performance remained essentially unaffected for gyroid inserts spanning up to 5%, with lift and drag coefficients maintained within experimental uncertainty. Tests with blocked permeability demonstrate that the observed effects stem from structural permeability rather than surface roughness. These findings establish gyroid inserts as a promising passive flow control for cavitation mitigation in marine propellers, hydrofoils, and turbomachinery, as well as noise control in aircraft wings and wind turbines, while preserving operational efficiency.</p>

Gyroid porous inserts as a novel flow control to mitigate tip vortex cavitation

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2026年5月23日

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Thomas Berger,
Mohamed Farhat

摘要

Tip vortices generated at the tip of lifting surfaces pose significant challenges in fluid dynamics, causing induced drag, noise, and cavitation erosion risk across aerospace and hydraulic applications. Among the various mitigation strategies, porous tips have been explored with mixed results, showing limited effectiveness in diffusing concentrated vorticity. In this study, we introduce a gyroid-based porous tip as a novel passive flow control device for tip vortex mitigation. A gyroid is a triply periodic minimal surface that forms a smooth and tortuous porous 3D network. A gyroid-based porous insert was attached to an elliptical NACA 16-020 hydrofoil tip (Re ≈ 9 × 10⁵), replacing 3%, 5%, and 9% of the span. Laser Doppler Velocimetry (LDV) measurements revealed that increasing the gyroid portion dramatically reduces maximum tangential velocity while enlarging the vortex core radius. The vortex circulation remains unchanged, indicating a diffusion mechanism that spreads concentrated vorticity over a larger core. At 12° incidence, the 9% gyroid insert reduced peak tangential velocity by a factor of 3.2 alongside a sixfold increase in vortex core radius. Consequently, the minimum pressure coefficient at the vortex center increased from $-1.4$ $- 1.4$ to $-0.1$ $- 0.1$ , reducing significantly the risk of cavitation. Flow visualization confirmed complete suppression of tip vortex cavitation across all tested conditions. The gyroid effectiveness was verified for both tripped and natural boundary layer transitions. Critically, hydrodynamic performance remained essentially unaffected for gyroid inserts spanning up to 5%, with lift and drag coefficients maintained within experimental uncertainty. Tests with blocked permeability demonstrate that the observed effects stem from structural permeability rather than surface roughness. These findings establish gyroid inserts as a promising passive flow control for cavitation mitigation in marine propellers, hydrofoils, and turbomachinery, as well as noise control in aircraft wings and wind turbines, while preserving operational efficiency.