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.

Three‐Dimensional Representation of Large‐Scale Structures Based on Observations in Atmospheric Surface Layers

“…This result is within the experimental error of such ASL observations suggested by the analysis of ASL experimental data in Metzger and Klewicki (), Kunkel and Marusic (), and Liu, Bo, et al. (). In addition, a comparison of the correlation coefficient at different Δ y values indicates that R uu decreases with increasing spanwise separation.…”

“…This is as expected because the ASL results reported in Liu, Bo, et al. () indicated that the inclination angle is approximately invariant when the reference height satisfies z ref <0.01 δ , while it increases with z ref at higher reference height. The inclined structure leads to an obvious streamwise shift of the horizontal section.…”

“…The full details of the experimental parameters are reported in Wang and Zheng (), Liu, Bo, et al. (), Liu et al. (), and Han et al.…”

A Predictive Model for the Streamwise Velocity in the Near‐Neutral Atmospheric Surface Layer

“…The streamwise velocity u was obtained by wind direction adjustment using the following formula: where u 0 and v 0 are the measured streamwise and spanwise velocities in the anemometer coordinate, respectively; the upper line means average. The measured data were split into multiple hourly time series to obtain converged statistics for the subsequent analysis (Hutchins et al, ; Liu, Bo, & Liang, ; Wang & Zheng, ). Our measuring height is between 0.9 and 30 m, which is approximately in the logarithmic region (Liu, Bo, & Liang, ; Liu, Wang, & Zheng, ; Wang & Zheng, ; Yang & Bo, ).…”

“…The measured data were split into multiple hourly time series to obtain converged statistics for the subsequent analysis (Hutchins et al, ; Liu, Bo, & Liang, ; Wang & Zheng, ). Our measuring height is between 0.9 and 30 m, which is approximately in the logarithmic region (Liu, Bo, & Liang, ; Liu, Wang, & Zheng, ; Wang & Zheng, ; Yang & Bo, ). Eleven CSAT3B anemometers were installed in a logarithmic manner in the vertical direction for z = 0.9, 1.71, 2.5, 3.49, 5, 7.15, 8.5, 10.3, 14.5, 20.9, 30 m. The friction velocity u τ and the aerodynamic roughness length z 0 were calculated by fitting the mean velocity profile through the least squares method based on the logarithmic law (Bagnold, ): where κ is the von Karman constant, typically equals 0.41.…”