A porous edge on turbine blades and aircraft wings reduces noise production

In aircraft and wind turbines, the majority of the noise produced comes from the turbulent air flowing around the wing or the blade known as the turbulent boundary-layer trailing-edge (TE) of the airfoil.

Replacing part of the airfoil with a porous metal foam can help mitigate some of this noise. Teruna et al. simulated the effects of this proposed solution to investigate the mechanisms that may work to reduce airfoil noise.

Among all the different effects that occur with a porous TE, the authors found the primary contribution to noise reduction comes from a pressure release process. As the pores cause the pressure fluctuations between the opposite sides of the airfoil to gradually reduce, the acoustic scattering is reduced as well, especially in the lower frequency range. The group also noted the airfoil angle-of-attack and the incoming airflow speed have relatively little impact on noise.

They observed these effects in simulations that computed the turbulence and noise caused by a solid TE, compared to one in which the last 20% of its length is replaced by a porous metal foam made of nickel, chromium and aluminum.

“A possible application for aircraft high-lift devices would be a sort of retractable perforated edge that extends the flaps, such that the perforated edge can be deployed during landing when the flap self-noise is the most apparent,” said author Christopher Teruna.

For industrial applications such as aircraft and wind turbine blades, additional practical aspects of the porous TE need to be addressed, such as determining how to properly clean and maintain the pores and understanding safety issues related to the material’s failure modes.

Source: “On the noise reduction of a porous trailing edge applied to an airfoil at lifting condition,” by Christopher Teruna, Francesco Avallone, Daniele Ragni, and Damiano Casalino, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0047512 .

This paper is part of the Lattice Boltzmann Method 2021 Collection, learn more https://aip.scitation.org/toc/phf/LBM2021/1?size=all">here .