On the impact of the stability of the marine atmospheric boundary layer on the wind profiles at Høvsøre during westerly winds

Søren Zebitz Nielsen

Studenteropgave: Semesterprojekt

Abstrakt

This thesis studies the behavior of the upper parts of the westerly wind profiles (260o – 280o) measured at the Danish National Test Site for Large Wind Turbines at Høvsøre in the north western Jutland. The westerly wind profiles from this site are complicated by different internal boundary layers due to the sites location not more than 1700 meters from the North Sea. The upper parts (80 – 160 meters) of the westerly wind profiles at the site are thought to be lying inside the boundary layer created over the North Sea since the internal boundary layer that grows as the air is advected from the sea over the land surface is supposed not yet to have grown higher than a maximum of 80 meters this short distance inland. Hence the wind speed in the upper parts of the wind profiles at the site is thought to dependent upon the stability of the upstream marine atmospheric boundary layer. The hypothesis is that the stability of the marine atmospheric boundary layer is the dominant player behind the behavior of the upper parts of the wind profiles at Høvsøre, and that it is possible to show an over speed effect in case of stable upstream atmospheric conditions compared to neutral conditions, and an under speed effect in unstable upstream conditions. The upstream stability is measured at the offshore wind farm at Horns Rev 120 km south west of Høvsøre under the assumption that the stability measured there is the same as just off the coast upstream of the site at Høvsøre. The upstream stability is quantified by assigning the different measurements of the stability of the marine atmospheric boundary layer into seven stability classes. By comparing measurements of the stability at Horns Rev with the simultaneous wind profile measured at Høvsøre it is possible to plot all wind profiles related to each of the seven upstream stability classes. In this way the behaviors of the upper parts of the wind profiles in relation to each upstream stability class can be analyzed, and by comparing the mean profiles calculated from all the wind profiles in each of the seven stability classes the difference between them can be seen. It is found that the results of this analysis agree with the hypothesis and it is concluded that the stability of the upstream marine atmospheric boundary layer has a considerable influence on the upper parts of the wind profiles at Høvsøre.

UddannelserFysik, (Bachelor/kandidatuddannelse) Bachelor el. kandidat
SprogEngelsk
Udgivelsesdato22 jan. 2009
VejledereTage Emil Christensen & Sven-Erik Gryning

Emneord

  • atmosphere
  • Atmospheric Boundary Layer
  • Horns Rev
  • meteorology
  • wind speed
  • Monin-Obukhov length
  • Høvsøre
  • internal boundary layers
  • wind energy
  • turbulence
  • wind profile
  • stability