How They Work
Our products are made with porous pile materials that interact with the wind to manage velocity and turbulence. Porous materials have benefits for airflow control by introducing a fluid-permeable medium that modifies airflow before it reaches the ear. Incoming turbulence is dissipated through fiber interaction, and there is a designed amount of air flow-through. Our products go well beyond simply blocking a portion of the oncoming wind.
PILE-FLOW INTERACTION
Fibers interact with the airflow to dissipate kinetic energy, reducing local velocity and coherent pressure fluctuations.
SHEAR LAYER DISPLACEMENT
The pile broadens and displaces the shear layer outward, moving peak shear, vorticity, and associated pressure fluctuations farther from the ear.
POROUS WAKE-PRESSURE RECOVERY
Bleed flow makes wake pressure less negative and reduces the velocity deficit, helping keep the shear layer farther from the ear
Our products reduce wind velocity and turbulence intensity.
And move the modified / weaker flow away from the outer ear.
Academic Analogies
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)
Viscous Dissipation
Pile greatly increases the surface area exposed to the airflow. At each fiber, the no-slip condition brings the air locally to zero velocity, creating microscopic velocity gradients that dissipate kinetic energy. Distributed across thousands of fibers, this surface interaction progressively slows the flow before it reaches the ear.
We follow the physics to quiet the wind.
Flow visualization at 20 mph to verify the above turbulence distribution.
As demonstrated above, pile material significantly modifies downstream flow.
(Left: AirStreamz Pile Material | Right: Simple Wind Blocking)
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
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(a- Kudo, T., Nishimura, M., Nishioka, M., Aerodynamic Noise Reducing Techniques by Using Pile-Fabrics., 5th AIAA/CEAS Aeroaoustics Conference., AIAA-Paper. (1999)
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(a- Nishioka, M., Vorticity Manipulation as an Effective Means for Aerodynamic Noise Reduction., The Eighth Asian Congress for Fluid Mechanics., Shenzhen, China. (1999)
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Nishioka, M., Aerodynamic Noise Suppression Technique Using Fur., Japan Society of Aeroacoustics and Astronautics, Osaka Prefecture University, Faculty of Engineering Dept. (2000)
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Nishimura, M., Goto, T., Kobayashi, K., Effect of Several Kinds of Pile-Fabrics on Reducing Aerodynamic Noise., Aeroacoustics Conference Presentation., Monterrey, California. (2005)
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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.