A nested multi-scale system implemented in the large-eddy simulation model PALM model system 6.0

Abstract. Large-eddy simulation (LES) provides a physically sound approach to study complex turbulent processes within the atmospheric boundary layer including urban flows. However, such flow problems often involve large separation of scales, requiring computational domain and very high grid resolution near surface features, leading prohibitive costs. To overcome this problem, an online LES–LES nesting scheme is implemented into PALM model system 6.0. The hereby documented evaluated method capable supporting multiple child domains, which can be nested their parent either in parallel or recursively cascading configuration. by first simulating purely convective then three different neutrally stratified scenarios with increasing order topographic complexity. results runs are compared corresponding non-nested high- low-resolution results. reveal that solution accuracy high-resolution nest clearly improved as solutions reference In obstacle-resolving LES, two-way coupling becomes problematic anterpolation introduces regional discrepancy obstacle canopy domain. This remedied introducing canopy-restricted where operation only performed above canopy. test simulations make evident most suitable strategy for LES. testify reduce CPU time up 80 % fine-resolution runs, while overhead from operations remained below 16 significantly less one-way alternative.