A Turbulence Model for the Stable Boundary Layer with Application to CFD in Wind Resource Assessment
In wind resource assessment, the impact of the atmospheric thermal stability attracts more and more attention.
The first reason is the increase of wind turbines height. The second reason is that the practice of WRA engineering is evolving towards a regular use of time series extrapolations (measurements or mesoscale data) or at least more detailed statistical analysis. Using time series instead of global statistics leads to considering more stable situations.
In CFD models, the turbulent fluxes are linked to the gradients of the mean variables via the concept of turbulent viscosity, considered as the product of a turbulent wind speed scale, and a turbulent length scale. Up to now, this approach failed to reproduce strong stability cases because of the underlying hypothesis of the Monin-Obukhov Similarity Theory (MOST).
We propose a multi-layer approach for the turbulent viscosity modeling by taking benefit of the k-L model which offers a very good adaptation to real atmospheric flows. This 3-L (three layers) model is implemented in the CFD software Meteodyn WT.