Scaling of turbulence spectra measured in strong shear flow near the Earth’s surface

• DOI: 10.1088/1402-4896/aa91b2
• Publication Date: 2017-11-02T09:31:51Z
• Authors: T Mikkelsen; S E Larsen; H E Jørgensen; P Astrup; X G Larsén
• Keywords: Wavenumber; Turbulence Modeling

Within the lowest kilometer of Earth's atmosphere, in so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to ground, turbulence is predominately generated by mechanical wall-bounded wind shear, whereas at higher altitudes turbulent mixing heat moisture also play a role. The variance (square standard deviation) fluctuation around mean speed measure kinetic energy content turbulence. This can be resolved into spectral distributions, or spectra, as functions eddy size, wavenumber, frequency. Spectra derived from Fourier transforms records space time corresponding wavenumber frequency respectively. Atmospheric spectra exhibit different subranges that distinguished scaled physical parameters responsible for: (1) their generation; (2) cascade across spectrum large- small-scale; (3) eventual decay owing viscosity effects on Kolmogorov microscale, which size only fraction millimeter. paper addresses part layer—the surface layer—where shear strong nonslip condition ground. Theoretical results dating back Tchen's early work 1953 'on flow' led Tchen predict production subrange with distinct inverse-linear power law for strongly sheared high-Reynolds number flow, encountered known layer. presents observations measured meteorological mast Høvsøre, Denmark, support prediction following degree −1 layer form where friction velocity wavenumber. theory shown able component parallel direction sizes larger than measurement height above An amended analytical model near-neutral then proposed. model, applicable scaling all heights obtained combination Kaimal's classical inertial 1954 proposed theory. production-amended compared ensemble-averaged selected during nine-month period recordings six sonic anemometers 10, 20, 40, 60, 80, 100 m tower test site large turbines Denmark. Finally, potential applications new discussed, particular use within one-third most prominent. supply wavenumber-resolved energies loads buildings, bridges, turbines, its parameterization used scale-dependent of, e.g., surface-released dispersion calculations regions close