Cup Anemometer Overspeeding.

A disadvantage of cup anemometers is the so-called overspeeding caused by their nonlinear response to fluctuating winds. In this paper, a statistical method is applied to a general cup-anemometer equation of motion to determine the overestimation of the mean wind speed in a turbulent wind. It is shown that the overspeeding depends both on the turbulence intensity and on the shape of the speed energy-spectrum. A formula for relative overspeeding is derived in terms of the horizontal and vertical turbulence intensities, the cup-anemometer distance constant, and a function of the ratio between this constant and the characteristic length scale of the horizontale turbulence. Overspeeding may amount to more than 10% only in those cases where the ratio between the cup-anemometer distance constant and the height of observation is of the order of 10 or more.