Controlling tip vortices, cavitation, and wakes through permeable tip treatment

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• Yabin Liu, CUED
• Wednesday 07 May 2025, 14:00-15:00
• JDB Seminar RM.

If you have a question about this talk, please contact Anna Walczyk.

Wind and tidal energy are essential to the global transition towards net-zero emissions. In 2024, wind energy contributed 30% to the UK’s electricity generation, underscoring its significance, while tidal power has the potential to supply up to 11% of annual electricity demand. Despite the considerable promise of renewable energy, vortex-induced phenomena, such as turbine wakes, cavitation, unsteady loads, and noise, remain significant obstacles to the full realisation of these resources. Among these, tip vortices, a long-standing challenge in wing- and blade-based systems, play a key role in cavitation formation, wake generation and propagation, noise emission, and delayed wake recovery.

To address these challenges, I have proposed and developed a passive, cost-effective solution: permeable tip treatment. Both CFD simulations and PIV measurements have been conducted on a wing and a model-scale horizontal-axis turbine, in a water tunnel and at the FloWave facility in Edinburgh. At the initial stage, a porous zone was modelled at the blade tip using Darcy’s law, revealing an optimal permeability that significantly reduces the intensity of tip vortices and the associated pressure drop, thereby decreasing the risk of cavitation. Notably, even with a spanwise extent of only 0.1% of the turbine diameter, the design can lead to an increase of up to 63% in the minimum pressure coefficient at the vortex core, at a Tip Speed Ratio (TSR) of 6. In addition, this approach shows great promise in enhancing wake recovery in both wind and tidal turbines. By expediting the breakdown and destabilisation of tip vortices downstream of the rotor, the wake recovery distance can be reduced by up to 20%, delivering a considerable improvement in the efficiency and energy output of turbine arrays in wind and tidal farms.

Building upon the above, we have developed and tested an innovative grooved-tip design, consisting of multiple grooves along the tip chord to generate an equivalent local 2D permeability. This configuration achieved approximately half the effect of a full 3D porous structure, presenting a practical alternative. We also examined the chordwise scope of the permeable region and found that the most effective suppression of tip vortices occurred when the grooved section was placed between the vortex detachment point and the blade’s trailing edge.

Future work will focus on developing refined permeable structures with targeted 3D permeability to more effectively control wake and cavitation, as well as simultaneously mitigating blade-tip noise through acoustic experiments and simulations. Through high-fidelity simulation and data-driven modal analysis, we will also characterise the influence of permeability on vortex breakdown and wake recovery across a representative range of Reynolds numbers and TSRs and understand the underlying physics.

This talk is part of the Engineering Fluids Group Seminar series.

This talk is included in these lists:

• Acoustics Lab Seminars
• Engineering Department Acoustics/Combustion Student seminars
• Engineering Fluids Group Seminar
• JDB Seminar RM

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