Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

Predição de Características de Turbulência Atmosférica Para Camada Limite de Superfície Usando Métodos Espectrais Empíricos

Abstract

Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k⁻¹ and k⁻³ slopes for Kolmogorov k^−5/3 law in inertial sub-range and k⁻⁷ in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3^rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

Keywords:
turbulence; wind speed; spectra; length scale; surface roughness