Rotors found on wind turbines, helicopters, and propellers generate wakes, which can have detrimental effects on downstream structures. These wakes are characterized by helical vortices shed from the tips of the rotor blades. Helical vortex systems are subject to instabilities that cause the vortices to decay, mitigating unwanted wake effects. Here we explore different ways to trigger these instabilities by adding imperfections to a small-scale experimental rotor. We try introducing a slight asymmetry to the rotor geometry (e.g., making one blade longer than the other two) and varying the rotation speed of the rotor. Using fluorescent dye to visualize the tip vortices, we can see that both methods successfully distort the vortex system. Numerical simulations show that neighboring helix loops get closer together when these imperfections are added, making vortex decay more likely. The methods explored here could be applied to industrial rotors such as wind turbines to reduce the negative impacts of their wakes.
This work is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License. Any reuse must credit the author(s) and provide a link back to this page.