Submitted as: model evaluation paper
11 Nov 2022
Submitted as: model evaluation paper | 11 Nov 2022
Status: this preprint is currently under review for the journal GMD.

Self-nested large-eddy simulations in PALM Model System v21.10 for offshore wind prediction under different atmospheric stability conditions

Maria Krutova, Mostafa Bakhoday-Paskyabi, Joachim Reuder, and Finn Gunnar Nielsen Maria Krutova et al.
  • Geophysical institute and Bergen Offshore Wind Centre, University of Bergen, Allégaten 70, 5007 Bergen, Norway

Abstract. Large-eddy simulation (LES) resolves large-scale turbulence directly and parametrizes small-scale turbulence. Resolving the micro-scale turbulence, e.g., in the wind turbine wakes, requires both a sufficiently small grid spacing and a domain large enough to develop the turbulent flow. Refining the grid locally via a nesting interface effectively decreases the required computational time compared to the global grid refinement. However, interpolating the flow between the nested grid boundaries introduces another source of uncertainty. Previous studies reviewed the nesting effects for a buoyancy-driven flow and observed a secondary circulation in the two-way nested area. Using nesting interface with a shear-driven flow in the wind field simulation, therefore, requires additional verification. We use PALM model system to simulate the boundary layer in a cascading self-nested domain under neutral, convective, and stable conditions, and verify the results based on the wind speed measurements taken at the FINO1 platform in the North Sea. We show that the feedback between the parent and child domain in a two-way nested simulation of a non-neutral boundary layer alters the circulation in the refined domain, despite the spectral characteristics following the reference measurements. Unlike the pure buoyancy-driven flow, the non-neutral shear-driven flow slows down in the two-way nested area and accelerates after exiting the child domain. We also briefly review the nesting effect on the velocity profiles and turbulence anisotropy.

Maria Krutova et al.

Status: open (until 21 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Maria Krutova et al.

Data sets

PALM v21.10 self-nested LES for three stability conditions Maria Krutova

Model code and software

PALM model system 21.10 ​PALM group at the ​Institute of Meteorology and Climatology (IMUK) of Leibniz Universität Hannover, Germany

Maria Krutova et al.


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Short summary
Local refinement of the grid is a powerful method allowing to reduce the computational time while preserving the accuracy in the area of interest. Depending on the implementation, the local refinement may introduce unwanted numerical effects into the results. We study the wind speed common to the wind turbine operational speeds and confirm strong alteration of the result when the heat fluxes are present, except for the specific refinement scheme used.