How They Work
Our products are made with porous materials that interact with the wind to manage both velocity and turbulence. Porous materials have benefits for airflow control by introducing a fluid permeable medium that modifies boundary layer, shear layer, and wake characteristics. Incoming turbulence is absorbed by the material and there is a designed amount of air flow-through. Surface interaction with the soft fibers reduces turbulence velocity / rotational intensity.
Our products reduce wind velocity and turbulence intensity.
And move the modified / weaker flow away from the outer ear.
Academic research supports utilizing porous pile materials to reduce wind turbulence and aerodynamic noise. As shown in the graphic below (5 m/s wind speed): "It is remarkable that the near-wall flow is very calm for the case of pile-fabric. We see that the separated shear layer is thicker and weaker for the pile-fabric compared with the smooth case. In fact, the streamwise position where the shear fluctuations become maximum is located at about x/d=2.5 for the pile-fabric while it is about x/d=0.4 for the smooth surface." - a)
The pile material makes the shear layer gentle and moves the maximum turbulent region away from the ear(s). In addition, flow resistance gently attenuates vortex motion and inhibits the acceleration of vortices. As a result, turbulent flow interaction with the ear(s) is reduced.
Flow visualization at 20 mph to verify the above turbulence distribution.
As demonstrated above, pile material significantly modifies downstream flow.
Loudness / Annoyance
In addition to masking surrounding sounds, wind noise can be annoying. While loudness can be the primary driver for annoyance, noise level variation / fluctuations and other spectral characteristics can also play a role. Accordingly, we incorporate additional tools, like spectrograms and Ln values / Statistical Noise Levels, Ln, L10, L90%, etc.
Related Research / References
(a- Kudo, T., Nishimura, M., Nishioka, M., Aerodynamic Noise Reducing Techniques by Using Pile-Fabrics., 5th AIAA/CEAS Aeroaoustics Conference., AIAA-Paper. (1999)
(a- Nishioka, M., Vorticity Manipulation as an Effective Means for Aerodynamic Noise Reduction., The Eighth Asian Congress for Fluid Mechanics., Shenzhen, China. (1999)
Nishioka, M., Aerodynamic Noise Suppression Technique Using Fur., Japan Society of Aeroacoustics and Astronautics, Osaka Prefecture University, Faculty of Engineering Dept. (2000)
Nishimura, M., Goto, T., Kobayashi, K., Effect of Several Kinds of Pile-Fabrics on Reducing Aerodynamic Noise., Aeroacoustics Conference Presentation., Monterrey, California. (2005)
Massaharu, N., Nishimura, M., Goto, T., Aerodynamic Noise Reduction by Pile Fabrics., Fluid Dynamics Research., Department of Mechanical / Aerospace Engineering, Tottori U., Japan. (2010)
Aero-acoustic engineering helps us develop the most effective products.