LES study of turbulent flow fields over a smooth 3-D hill and a smooth 2-D ridge

Large eddy simulation is applied to study the turbulent flow fields over a 3-D hill and a 2-D ridge with smooth ground. The mean velocities as well as the turbulent fluctuations are computed. Fairly good agreements with experiments validate the accuracy of the numerical model applied in this study. The spectra of the velocities in the wake of the 3-D hill and 2-D ridge, and those over the flat terrain, are calculated. Spectra of velocity fluctuations at selected locations in the wake of topographic features are well reproduced. The examination of spectra shades some lights on the dynamics of the turbulent flow. It is found that the spectra of fluids in the wake are sensitive to the oncoming turbulence condition for the 2-D ridge, which is not true for the 3-D hill. Non-isotropic characteristics of turbulence in the near-wake of topographic features are examined using ratios of Reynolds stress which are also compared with those in IEC 61400-1 (2005).