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An experimental study of the profiles of wind speed, shearing stress and turbulence at the crest of a large hill
Author(s) -
Bradley E. F.
Publication year - 1980
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710644708
Subject(s) - turbulence , crest , wind speed , mechanics , reynolds stress , meteorology , turbulence kinetic energy , roughness length , geology , physics , geometry , atmospheric sciences , wind profile power law , mathematics , optics
Measurements have been made, under neutral conditions, of the turbulent wind structure on a 100m tower at the crest of a hill of height h = 170m. A local velocity maximum, or ‘jet’, was observed at about h /5, below which the ratio of increase in wind speed to the upwind value at the same height was 1.07, and almost independent of height near the surface. The r.m.s. turbulence components σw σv and σw were also approximately doubled near the surface, but whereas σu and σv both decreased with height, the surface increase in σw extended over the entire height of measurement. Reynolds stress was almost uniform above the ‘jet’, but increased sharply towards the surface, to 3–5 times the upwind value. Departures from neutrality affected the profile shape and the magnitude of turbulence fluctuations very markedly. Although the size of hill lay outside the range of validity of an analytical theory of Jackson and Hunt, their expressions for velocity and horizontal pressure gradient were in good agreement with the observations. Numerical theories by Frost, Harper and Fichtl and by Taylor, for hills of different shape, but similar slope to the experimental hill, also produced values of surface stress and velocity increase of the magnitude observed.