Why elliptical anemometer cup shape is better

What are the advantages of MeteoWind’s elliptical cups? Elliptical shape offers an aerodynamic advantage for cups traveling upwind. Elliptical shape exhibits less drag than any other cup shape for the upwind half of an anemometer’s rotation. While on the downwind half of its rotation it offers a positive increase in drag over many other cup shapes including circular or conical cup shapes of current state of the art anemometers. –Independent anemometer accuracy & linearity wind tunnel test results: Windguard, DE

High accuracy in updrafts and downdrafts

Elliptical anemometer shape and flat rotor mean negligible over-speeding due to non-horizontal airflow (upflow and downflow around hills, cliffs, sand dunes, buildings and large scale turbulence). This is a major concern for accurate weather monitoring and wind resource assessment studies.

High response rate (low distance constant)

Very few anemometers offer high response rates like our Elliptic Anemometer 2 and the all metal MeteoWind 2 anemometers with wind vanes. Positive response rate of an anemometer is known as an anemometer’s distance constant. It refers to how far past the anemometer air gets before the anemometer has had a chance to catch up to the increase in wind speed (lower distance constant is better). It is usually validated by wind tunnel tests. Our MeteoWind 2 elliptic anemometer as tested by WindGuard in Germany, an independent laboratory, offers one of industry’s best (lowest) distant constants of 1.6 m at 8 m/s which is a faster response time than most ultrasonic anemometers offer. MeteoWind Compact offers an even faster response.

• MeteoWind 2 mean time constant and step response: 0.2 sec @ 8 m/s. – Independent anemometer response rate (distance constant) wind tunnel test results: Windguard, DE

Minimum over speed

Our elliptical anemometers have very low overspeeding due to their light weight rotors. Overspeed in turbulent airflow and gusty wind conditions is another significant source of wind speed measurement error. If wind slows down very quickly, as in turbulent and gusty wind conditions, all cup anemometers show higher wind speed readings until they have had a chance to slow down to match the new lower wind speed. This delay and resultant error in readings can last for few tenths of a second in high-performance anemometers like the MeteoWind 2 to a few seconds in other devices due to their rotor weight and inertia.

Effective snow shedding and minimal icing buildup

While the elliptical anemometer cup shape offers aerodynamic advantages, it is also very good at minimizing snow and ice buildup and effective at snow and ice shedding. The elliptical cup shape offers the advantage of flatness. Our cups are the flattest on the market today. Due to this flatness, snow and ice have very little surface to hold on to and to resist centrifugal snow shedding forces as the anemometer rotates. Resisting snow and ice buildup means higher and more consistent accuracy readings during all weather conditions without the need for expensive anemometer heating. (MeteoWind 2 and MeteoWind Compact are also available with heating for extreme weather reliability.)

• Elliptical cups have low drag and clean flow separation regions resulting in aerodynamically efficient, consistent and stable anemometer performance.

• Spherical cups have unstable boundary layer separation regions resulting in aerodynamic instabilities affecting repeatability and consistency of wind speed measurement.

• Conical cups have clean flow separation regions but large aerodynamic drag negatively affecting anemometer response time.

• Elliptical cups have a consistently longer moment arm for wind to push against, benefiting anemometer measurement consistency and response time. (For equivalent cup area & rotor diameter)

• Circular cups have their center of pressure closer to the anemometer rotation axis, thus reducing the aerodynamic moment arm to overcome anemometer inertia and friction effects.

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