Application of a Large Eddy Simulation Database to Optimization of First Order Closures for Neutral and Stably Stratified Boundary Layers
Large-eddy simulation (LES) is a well-established numerical technique, which resolves the most energetic turbulent fluctuations in the planetary boundary layers. Averaging these fluctuations, high-quality profiles of mean values and turbulence statistics can be obtained in experiments with well-defi...
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Main Authors | , |
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Format | Journal Article |
Language | English |
Published |
21.12.2006
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Subjects | |
Online Access | Get full text |
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Summary: | Large-eddy simulation (LES) is a well-established numerical technique, which
resolves the most energetic turbulent fluctuations in the planetary boundary
layers. Averaging these fluctuations, high-quality profiles of mean values and
turbulence statistics can be obtained in experiments with well-defined initial
and boundary conditions. Hence, the LES data can be beneficial for assessment
and optimization of turbulence closure schemes. A database of 80 LES runs for
neutral and stably stratified PBLs (DATABASE64) is applied in this study to
optimize the first-order turbulence closure (FOC). Approximations for the
mixing length scale and stability correction functions have been tuned to
minimise a relative root-mean square error over the entire DATABASE64. New
stability functions have correct asymptotes describing regimes of strong and
week mixing found in theoretical exercises, atmospheric data and LES. The
correct asymptotes exclude the need for a critical Richardson number in the FOC
formulation. Further, we analysed the FOC quality as functions of the integral
PBL stability and the vertical model resolution. We show that the FOC is never
perfect because the turbulence in the upper half of the PBL is not generated by
the local gradients. Accordingly, the parameterized and LES fluxes decorrelate
in the upper PBL. With this imperfection in mind, we show that there is no
systematic quality deterioration of the FOC in strongly stable PBLs provided
the vertical model resolution is better than 10 levels within the PBL. In
agreement with previous studies, we found that the quality improves slowly with
the vertical resolution refinement. It is generally wise to not overstretch the
mesh in the lowest 500 m of the atmosphere where majority of the observed,
simulated and theoretically predicted stably stratified PBLs are located. |
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DOI: | 10.48550/arxiv.physics/0612206 |