Aerodynamic vs. acoustic performance: a balancing act

An emission-free source of sustainable energy, wind power reduces carbon dioxide emissions and air pollution. A leading challenge in the development of wind turbines is to mitigate noise pollution while maintaining efficiency.

In wind tunnel experiments, permeable trailing edges have overcome the limitations of standard industrial solutions to noise mitigation. Adapting this noise control technique to more realistic environments requires a good understanding of its working mechanism.

To achieve it, Carpio et al. studied turbulent flow over a metal foam trailing edge of an airfoil to observe the effects on far-field noise of the permeability of the material and the hydrodynamic exchange, or communication, between two sides of the airfoil.

The authors proved noise mitigation is fundamentally related to the flow communication between each side of the blade.

“Communication decreases the noise scattering efficiency of the edge and allows for noise emission from different chordwise locations, which may interfere among each other,” author Alejandro Carpio said.

The authors’ solution was to design new trailing edges, which take advantage of the hydrodynamic exchange by linking both sides of the blade with straight cylindrical channels. The authors expect the simplicity of their channeled trailing edges make them good candidates for application in wind turbines soon.

“They believe to maintain a healthy balance between aerodynamic efficiency and acoustic performance, there must be a balance between appropriately choosing the length of permeable extension and increasing permeability closer to the edge of the airfoil.”

Source: “Mechanisms of broadband noise generation on metal foam edges,” by Alejandro Rubio Carpio, Francesco Avallone, Daniele Ragni, Mirjam Snellen, and Sybrand van der Zwaag, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5121248 .