Scale-adaptive turbulence modeling for LES over complex terrain
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ORIGINAL ARTICLE
Scale‑adaptive turbulence modeling for LES over complex terrain Md. Abdus Samad Bhuiyan1 · Jahrul M. Alam1 Received: 26 April 2020 / Accepted: 30 September 2020 © Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract The large-eddy simulation (LES) is an efficient method for the study of atmospheric boundary layer (ABL) flow over complex terrain. However, the robustness of LES is influenced by dynamics methods for the subgrid-scale stress, which remains one of the challenging issues. Here, we present a scale-adaptive LES methodology to study ABL flow over complex terrain. We present a canopy stress method for LES over complex terrain, which provides no-slip and shear-stress boundary conditions using a cost-effective Cartesian mesh. We consider measurements from wind tunnel experiments for the investigation of a scale-adaptive subgrid-scale modeling framework for LES of wind flow over a hilly terrain. A flow simulation is then performed on six cases of ABL flow over an idealized complex terrain. The LES result is also compared against the measurement of wind over Askervein hill. The dynamic and non-dynamic versions of the turbulence kinetic energy-based subgrid model are also considered to illustrate the scale-adaptive nature of subgrid-scale turbulence. It was observed that ignoring scale-adaptivity of subgrid turbulence, LES can under-predict shear-stress, turbulence kinetic energy, and other statistical measures of atmospheric turbulence. Keywords Complex terrain · Turbulence · Subgrid-scale closure · Canopy stress
1 Introduction In large-eddy simulation (LES) of flow over mountainous regions, it is important to model the exchange of momentum between the atmospheric boundary layer (ABL) and a complex terrain. This article demonstrates a scale-adaptive LES method that engages the vortex stretching mechanism for dynamic modeling of atmospheric exchange over complex terrain. Such exchange processes between the land surface and the ABL over mountains were thoroughly investigated by several field measurements of wind over mountains [5, 7, 18, 26, 27]. In numerical weather prediction (NWP) models, the parameterization of earth–atmosphere exchange processes is empirically tuned, and thus, it becomes inherently uncertain in predicting the transition of meteorological scales and the land–atmosphere interaction [20]. For * Jahrul M. Alam [email protected] Md. Abdus Samad Bhuiyan [email protected] 1
Department of Mathematics and Statistics, Memorial University of Newfoundland, St. John’s, NL A1C5S7, Canada
example, grid cells become highly skewed if a steep mountain is resolved with the classical terrain-following coordinate systems that are typical in NWPs (see Figure 1). As it was detailed in [25] and in a number of recent articles [3, 23, 24], such a fine grid along with the classical parameterization may be a computational burden which deteriorates numerical errors of NWPs at finer grid resolutions if the terrain following system is retained. In contrast, the largeeddy simulation (LES) met
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