Car-Ears AirStreamz vs. Wind-Blox Pro
The importance of materials engineering cannot be overstated. Characteristics like texture, porosity, permeability (K), resilience, diffusion (D), etc. are evaluated / combined to meet internal and external flow requirements across a range of wind speeds and turbulence levels. In this regard, we are the only cycling related wind noise reduction (WNR) company to hold a utility patent (#US 9078482 - Sound Permeable Wind Noise Reduction Device).
Wind-Blox claims to use "Patented Wind-Blox Technology" to reduce wind noise. Having purchased and tested the various Wind-Blox products, it appears that the technology is limited to a small piece of closed cell foam covered with a nondescript fabric. They do, however, claim that Wind-Blox products are designed to "look hi-tech".
Exhaustive testing ensures that our products are the most effective of their kind on the market. We use precision audio recording equipment, spectral analysis software, CT (hot-wire) anemometers / pressure probes, and high resolution imaging tools. In addition to 'stress testing' in 'designed use' environments, we incorporate laboratory testing in custom built facilities in Colorado (Wind Jet) and New Jersey (Wind Jet Hydrodynamic Flume).
Wind flow patterns over the face / cheek and how it interacts with the pinna varies by speed and turbulence level.
AirStreamz are made from a soft porous material that interacts with oncoming wind to reduce velocity and turbulence intensity (i.e. diffuse vortical structures in turbulent flow). In this regard, porous material has benefits for flow-control by introducing a fluid permeable medium that modifies the boundary layer / wake characteristics. Over the last several years, a number of researchers have studied the flow over and through porous bluff bodies to reveal this flow control phenomenon. Please contact us if you would like to learn more about this research.
Wind noise tends to be lower frequency. We evaluate materials that focus on the important frequency ranges.
Wind Flow Depiction
Passive control of wind using porous material vs. bluff body flow instabilities (typically by the wake vortices).
Fig. 1: Depiction of wind flow interacting with porous material (AirStreamz) vs. a bluff (wind blocking) body.
Regarding base bleed, there is a relationship between base bleed pressure and wake / vortex formation (i.e. distance from flow separation). And turbulence (intensity) is an instability primarily generated by the free shear layer. With critical permeability, the free shear layer can be elongated significantly (away from / above the ear). In addition, by allowing some air to passively flow through, there is less higher velocity air / wind to divert over the ear.
Wind Flow Visualization
The wind flow / interaction characteristics noted above can be seen in the wind tunnel visualizations below:
Fig. 2: Flow visualization with smoke and laser sheet. Porous material interaction vs. bluff / blunt body turbulence.
It's important to remember that: "bluff bodies are characterized by a more or less precocious separation of the boundary layer from their surface, and by wakes having significant lateral dimensions and normally unsteady velocity fields." (Bluff Body Aerodynamics, Lecture Notes by G. Buresti, Dept. of Aerospace Engineering, University of Pisa, Italy)
Wind Flow Measurements
Using pressure sensors / hot-wires, the wind flow / interaction characteristics noted above are measured below (fig. 3). Velocity over the AirStreamz decreases due to the porous material interaction. In addition, a small amount of air flows though the product (under the strap) as base bleed - which helps stabilize the wake. Velocity over the Wind-Blox product remains strong and immediately contributes to wake instabilities / vortices into the concha. It should also be noted that turbulence increases with free stream velocity. Base bleed conveniently increases with velocity.
Fig. 3: a) Kurz hotwire anemometer probe placed adjacent to the WNR products. b) Pressure probes placed adjacent to the WNR products and at the rear of the concha. c) TrueRTA / oscilloscope to display turbulent pressure fluctuations.
In addition to the above measurements, we also use a differential pressure (pitot tube) manometer to measure static and dynamic pressure(s) around the products and outer ear. Measurements confirm that Wind-Blox create a significant low pressure (wake) zone on the leeward side. AirStreamz base bleed reduces this low pressure problem so turbulent (noise producing) wind flow stays farther away from the outer ear.
Other Aero / Acoustic Considerations
Wind-Blox are relatively stiff / inflexible. They can produce their own aeroacoustic (self) noise at higher speeds.
Wind-Blox incorporate known sound blocking (i.e. closed cell foam) material. This presents an obvious problem.
All Cat-Ears / AirStreamz products are made from soft materials that don't generate aeroacoustic noise. In addition, our proprietary materials have been independently tested at Antioch University for acoustic transparency (i.e. they don't block the sounds that a cyclist needs to hear). At Cat-Ears / AirStreamz, we take cycling safety seriously.
Customer Satisfaction | Amazon Reviews
A comparison of AirStreamz vs. Wind-Blox Pro customer reviews is below. In our opinion, customer satisfaction is the ultimate performance measurement. In this regard, the reviews appear to contradict the Wind-Blox claim that their products have "the highest rating of any bicycle wind blocking alternative". This claim lacks credible substantiation.
Related Reading / Scholarly Articles
The phenomenon of vortex shedding behind bluff bodies has been known since the days of Leonardo da Vinci...
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids 2004; 46:415–433 (DOI: 10.1002/fld.756)
E. Sanmiguel-Rojas, A. Sevilla, C. Martínez-Bazán, Jean-Marc Chomaz. Global mode analysis of axisymmetric bluff-body wakes: Stabilization by base bleed. Physics of Fluids, American Institute of Physics, 2009, 21, pp.114102. ff10.1063/1.3259357ff. ffhal-01002591f
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