Abstract
Large-eddy simulations are widely used to study flows in the atmospheric boundary layer. As atmospheric boundary-layer flows of different atmospheric stratification have very different flow characteristics on different length scales, well-resolved simulations of these flows require very different meshes. The Parallelized Large-Eddy Simulation Model combined with a realizable dynamic subgrid model is used to identify the best method for evaluating the resolution requirements for boundary-layer flows simulated by large-eddy simulations. In particular, we consider three atmospheric boundary-layer set-ups with different stratifications (stable, neutral, convective) to investigate how the quality of the simulation changes with the grid resolution. By following the work of Davidson (Int J Heat Fluid Flow 30(5):1016–1025, 2009), the results are examined using criteria such as the convergence of mean profiles, the ratio of modelled and resolved turbulence kinetic energy, and the two-point correlation. We conclude that the two-point correlation is the best measure to evaluate whether the resolution demands for a specific flow are fulfilled.
Highlights
Large-eddy simulation (LES) is a powerful tool for the investigation of atmospheric boundarylayer (ABL) flows (Mason 1994; Porté-Agel et al 2000; Kosovicand Curry 2000), such as flow downstream of wind turbines and within wind farms in both neutral and non-neutral stability (Calaf et al 2010; Porté-Agel et al 2011; Witha et al 2014; Abkar and Porté-Agel 2015; Dörenkämper et al 2015; Vollmer et al 2015), and the flow above urban areas of very complex topology (Letzel et al 2008; Park et al 2012).The LES approach aims to explicitly resolve the large-scale motions of the turbulent flow, while modelling the sub-filter motions
The sensitivity of the convective boundary layer to the LES grid resolution has been addressed by Sullivan and Patton (2011), who found that the majority of low-order-moment statistics become independent of the grid resolution when zi /Δ > 60, where zi is the height of the convective boundary layer and Δ is the size of a grid cell
We present the effects of grid size by first illustrating how the grid affects the mean flow and turbulence variables, and by analyzing how these grid effects are related to the flow resolution as predicted by several resolution criteria
Summary
Large-eddy simulation (LES) is a powerful tool for the investigation of atmospheric boundarylayer (ABL) flows (Mason 1994; Porté-Agel et al 2000; Kosovicand Curry 2000), such as flow downstream of wind turbines and within wind farms in both neutral and non-neutral stability (Calaf et al 2010; Porté-Agel et al 2011; Witha et al 2014; Abkar and Porté-Agel 2015; Dörenkämper et al 2015; Vollmer et al 2015), and the flow above urban areas of very complex topology (Letzel et al 2008; Park et al 2012).The LES approach aims to explicitly resolve the large-scale motions of the turbulent flow, while modelling the sub-filter motions. The sensitivity of the convective boundary layer to the LES grid resolution has been addressed by Sullivan and Patton (2011), who found that the majority of low-order-moment statistics become independent of the grid resolution when zi /Δ > 60, where zi is the height of the convective boundary layer (inversion height) and Δ is the size of a grid cell. They observed that the growth of the boundary layer is a sensitive measure of the LES solution convergence, since it becomes grid independent when the entrainment region is sufficiently resolved. He investigated the influence of the resolution on several measures, and concluded that the two-point correlation is the best method for estimating the required LES resolution in the case of a channel flow
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
