The Sphere Anemometer – A Fast Alternative to Cup Anemometry

Abstract

The main problem of cup anemometry is the different response time for increasing and decreasing wind velocities due to its moment of inertia. This results in an overestimation of wind speed under turbulent wind conditions, the so-called over-speeding. Additionally, routine calibrations are necessary due to the wear of bearings. Motivated by these problems the sphere anemometer, a new simple and robust sensor for wind velocity measurements without moving parts, was developed at the University of Oldenburg. In contrast to other known thrust-based sensors, the sphere anemometer uses the light pointer principle to detect the deflection of a bending tube caused by the drag force acting on a sphere mounted at its top. This technique allows the simultaneous determination of wind speed and direction via a two-dimensional position sensitive detector.

The behaviour of the newly designed sensor under turbulent conditions was investigated by comparative measurements of gusty wind using the sphere anemometer, cup anemometer and a hot-wire as a reference. It turned out that the sphere anemometer provides a better temporal and spatial resolution than cup anemometers do.