Materials Engineering

To reduce unwanted wind noise, one needs to match acoustic material to the specific characteristics of the oncoming wind. What’s more, the product’s final shape can affect the performance of its materials. A precise understanding of the aero-acoustic characteristics, such as its performance at certain frequencies, is essential.

 

Combining materials with different unique physical properties allows us to create the most effective wind noise reduction (WNR) products available.  We select materials and incorporate material coatings based on:

  • WNR performance characteristics that effect fiber behavior in turbulent air flow, such as fiber density, length, bending strength, resiliancy,  moisture regain, and elasticity.

  • Acoustic characteristics such as sound transmission / transparency (so important sounds are not blocked).  This is particularly important for sound source identification and localization.

  • Comfort characteristics such as air permeability, moisture wicking, heat transmission, hypoallergenic, and non-itch

  • Durability characteristics such as tensile strength, chemical resistance, abrasion resistance, and UV light resistance

  • Style characteristics - Visual "appeal," surface texture, tactile "feel," shaping, etc.

  • Production characteristics - Seam strength / distortions, pressing, bond ability, dye absorption, etc.

For example, turbulent air flow, when passing over a pile fabric material, experiences a slight reduction in energy as the pile fibers deform and act as tiny "shock absorbers."  In the immediate vicinity of the fabric, these "shock absorbers" reduces the intensity of rotational (vortex) air flow, which in turn reduces the air pressure fluctuations we perceive as wind noise.  Material properties of the fibers - such as stiffness, elasticity, etc.  - as well as the properties of the fabric - such as  fiber density, fiber length , porosity - have major effects on the effectiveness of WNR.

Related Academic Research

Considerable academic research supports the use of pile materials to reduce wake turbulence / aerodynamic noise.  As shown in the graphic below (hotwire measurements at 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 much thicker and thus much weaker for the case of pile-fabric compared with the smooth case.  In fact, the streamwise position where the shear fluctuation becomes maximum is located at about x/d=2.5 for pile-fabric, while it is about x/d=0.4 for the smooth surface." -a) 

Video 1: Flow visualization at 20 mph to help understand / verify the above noted turbulence distribution.

Faux Fur / Legacy Materials Engineering

Our original testing followed Thomas Edison's approach when he invented the light bulb.  Lots of negative and less than satisfactory performance  as we road tested iteration after iteration after iteration.  We eventually discovered the unique effectiveness of certain fabric materials, which led to testing nearly 100 different faux fur combinations of pile length, fiber density, shape, etc., etc.  Since then, we have re-tested many of these original materials using our latest aeroacoustic testing capabilities.  Re-testing materials helps ensure that we understand what works.    

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 Astroautics, 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)

Aeroacoustic engineering helps us develop the most effective products.

Cat-Ears / AirStreamz is a leading manufacturer of aero-acoustically designed passive wind noise reduction products.  Tested and recommended by respected publications and professionals, Cat-Ears / AirStreamz are the highest-rated and best-selling products designed for serious cyclists / outdoor sports enthusiasts.  Our products are 100% Satisfaction Guaranteed and Made in the USA.

Aeroacoustic Engineering Research and Product Development | Cedaredge, Colorado

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