Some Features of the Spatial Structures of the Surface Layer Turbulence in the High Wind Condition

Abstract

θThe present paper deals with the spatial structures of atmospheric turbulence in terms of the coherence and the phase of velocity fluctuations between two points. It is shown by reanalyzing the observed wind data that the decay factor of coherence is not constant, but function of both separation distance l and wind-anemometer line angle θ. However, for a longitudinal direction, the decay factor appears to be constant and the phase is obtained like that as deduced from Taylor's hypothesis. The following empirical formula of the decay factor is obtained at the height of 41.5m in high wind condition:
k_l=acosθ+b(lsinθ/z)^Csinθ where a, b and c are constants and z is a height of observation level. At the height of 41.5m in high wind conditions, estimated value of a is nearly equal to 2.6 or 3.8 and those of b and c are 14 and 0.45, respectively. The decay factors for lateral separations seem to
decrease with increasing roughness length.
Space correlations are computed as function of the wind-anemometer line angle by using the experimental formulae of power spectrum, coherence and phase. The calculated results agree well with the experimental ones within the range of their scattering.