A New Wall Shear Stress Model for Atmospheric Boundary Layer Simulations

Abstract

A new wall shear stress model to be used as a wall boundary condition for large-eddy simulations of the atmospheric boundary layer is proposed. The new model computes the wall shear stress and the vertical derivatives of the streamwise velocity component by means of a modified, instantaneous, and local law-of-thewall formulation. By formulating a correction for the modeled shear stress, using experimental findings of a logarithmic region in the streamwise turbulent fluctuations, the need for a filter is eliminated. This allows one to model the wall shear stress locally, and at the same time accurately recover the correct average value. The proposed model has been applied to both unique high Reynolds number experimental data and a suite of large-eddy simulations, and compared to previous models. It is shown that the proposed model performs equally well or better than the previous filtered models. A nonfiltered model, such as the one proposed, is an essential first step in developing a universal wall shear stress model that can be used for flow over heterogeneous surfaces, studies of diurnal cycles, or analyses of flow over complex terrain.

Perturbations to the Spatial and Temporal Characteristics of the Diurnally-Varying Atmospheric Boundary Layer Due to an Extensive Wind Farm

“…As bottom boundary conditions, a zero vertical velocity is imposed for the vertical component of the momentum equations, while an equivalent surface shear stress is imposed for the horizontal components. The shear stress is parametrized using Monin-Obukhov similarity theory (Monin and Obukhov 1954), suitably adapted for LES using a methodology developed by Bou-Zeid et al (2005) and Hultmark et al (2013). The atmospheric stability correction functions developed by Brutsaert (1992) are used with the scalar surface roughness length taken to be one tenth of the aerodynamic roughness length (Brutsaert et al 1989).…”

Dependence of near‐surface similarity scaling on the anisotropy of atmospheric turbulence

“…In this regard, the validity of surface layer similarity relations has been evaluated in terms of quasi-steadiness and local homogeneity (e.g., Brutsaert, 1982;Sugita and Brutsaert, 1990;Bou-Zeid et al, 2005;Wyngaard, 2010;Hultmark et al, 2013;Babić et al, 2016a;2016b), through numerical simulations (e.g., Khanna and Brasseur, 1997;Bou-Zeid et al, 2007;Stoll and Porté-Agel, 2009) and data obtained in several experimental field campaigns located in places ranging from quasi-perfect horizontal homogeneity (Kaimal and Finnigan, 1994) to highly complex terrain (e.g., Martins et al, 2009;Nadeau et al, 2013;Stiperski and Rotach, 2016), and complex atmospheric conditions (e.g., Grachev et al, 2013;. From these results, procedures and rules-of-use have been developed to ensure appropriate use of similarity relationships.…”

A Generalized Evaporation Model for Chinese Pans

“…The value of n optimized by Lim et al () for US Class A pans under nonsteady state conditions was 0.1, which was smaller than 0.57. For nonsteady state conditions, due to the turbulent airflows, the vertical wind speed could be larger than the horizontal wind speed (Haghighi & Or, , ; Hultmark et al, ). Therefore, the value of n under nonsteady state conditions could be smaller than that under steady state conditions.…”