Continuous computation of the standard deviations of longitudinal and lateral wind velocity components

Abstract

A technique is described for continuously evaluating the frequency spectra of wind gusts both along and at right angles to the mean wind direction. An anemometer of new design and a resolver provide electrical voltages linearly proportional to the wind velocity components in two mutually perpendicular directions. These voltages are applied directly to filter circuits, and recordings are made for various frequency bands, of the standard deviations of the velocity components in both directions. The magnitudes of the longitudinal and lateral velocity fluctuations are then obtained by applying pre-computed conversion factors which are functions only of the departure of the mean wind direction from the orientation of the resolver, and the ratio of the recorded standard deviations. Data have been selected from recordings made continuously over two periods of 11 days, and a short analysis of the longitudinal and lateral (horizontal) velocity fluctuations at a height of 4 m is presented for three frequency bands in the range 5 to 0.025 cycles per min. The magnitude of eddy velocity and the gustiness of the components are related to wind speed and atmospheric stability. Longitudinal fluctuations are usually greater, and in stable conditions exceed lateral fluctuations by factors up to 1.8, but at low frequencies, in unstable conditions, lateral fluctuations pre-ponderate.