Turbulent boundary layer simulations and models

Atmospheric profiles, stability, and forcing

With collaborators, I develop analytical descriptions of how surface forcing, stratification and Earth’s rotation set wind profiles and turbulent fluxes. The advance is to connect the vertical structure to these physical controls, with distinct closures and simulation tests for each regime. These studies inform wind-farm models, with separate evidence for each regime.

• Conventionally neutral wind profiles and geostrophic drag: surface-neutral layers capped by stable stratification; the free atmosphere remains part of the problem.
• Convective boundary layers: mean wind, potential temperature, and flux profiles under surface heating.
• Nocturnal stable boundary layers: momentum fluxes and wind deficits under stable stratification.
• Baroclinic wind-farm boundary layers: vertically varying geostrophic forcing and its implications for farm flow.

The linked studies state their forcing, closure assumptions, and comparisons with simulations. These results do not establish one validated model for arbitrary evolving weather.

Low-level jets connect atmospheric structure to turbine-scale and farm-scale flow. Related simulations examine how jet height affects blade loading and near-wake vortices and how a finite wind farm interacts with a jet in a stable boundary layer.

Testing large-eddy simulation against turbulence statistics

In Stevens et al., J. Fluid Mech. 757, 888-907 (2014), we performed large-eddy simulations (LES) of very-high-Reynolds-number turbulent boundary-layer flow and focused on profiles of the variance and higher-order moments of the streamwise velocity fluctuations. Figure 1a shows that high-resolution simulations with the scale-dependent Lagrangian subgrid model capture the velocity fluctuations and logarithmic law for the variance well, while lower-resolution simulations using the standard Smagorinsky model do not.

The logarithmic law for the mean velocity has long provided a robust reference for theories, models and simulations of wall-bounded turbulence. High-Reynolds-number experimental data show that the variance and higher-order moments of streamwise velocity fluctuations also display logarithmic laws. The LES yields approximate logarithmic laws for these higher-order moments, providing more demanding measures of accuracy, as highlighted in the Focus on Fluids article by Elie Bou-Zeid.

After validating the simulation results against experimental data, we used the simulation database to develop and test an analytical wavenumber-frequency model for space-time correlations in atmospheric-boundary-layer simulations [2], [3], [4].