The variation of large-scale structure inclination angles in high Reynolds number atmospheric surface layers

Abstract

Field observations were performed to explore the variation of large-scale structure inclination angles in the high Reynolds number atmospheric surface layer (ASL). The high Reynolds number flow measurements [Reτ ∼ Ο (106)] were acquired at the Qingtu Lake observation array site. The structure inclination angles inferred from two-point correlations of the fluctuating streamwise velocity were obtained for different friction velocities in the neutral regime and different thermal stability conditions. Results indicate that, in addition to the Monin− Obukhov stability parameter, the structure inclination angle varies systematically with the friction velocity in the neutral surface layer. An empirical model is proposed to parametrize the variation of the inclination angle with the normalized friction velocity. The empirical formula agrees well with both the current ASL results and the previously documented results. Further analysis suggests that the inclination angle is dominated by the vertical velocity gradient (vertical wind shear) for both neutral and non-neutral regimes. The present work contributes to a better understanding of the inclination angle for the large-scale structures and may be used to improve the existing wall-models in the large-eddy simulation of the ASL.