Journal Article
Wind Energy Science, vol. 3, iss. 2, pp. 589-613, 2018
Authors
Jeffrey D. Mirocha, Matthew J. Churchfield, Domingo Muñoz-Esparza, Raj K. Rai, Yan Feng, Branko Kosović, Sue Ellen Haupt, Barbara Brown, Brandon L. Ennis, Caroline Draxl, Javier Sanz Rodrigo, William J. Shaw, Larry K. Berg, Patrick J. Moriarty, Rodman R. Linn, Veerabhadra R. Kotamarthi, Ramesh Balakrishnan, Joel W. Cline, Michael C. Robinson, Shreyas Ananthan
Abstract
Abstract. The sensitivities of idealized large-eddy simulations (LESs) to variations of
model configuration and forcing parameters on quantities of interest to wind
power applications are examined. Simulated wind speed, turbulent fluxes,
spectra and cospectra are assessed in relation to variations in two physical
factors, geostrophic wind speed and surface roughness length, and several
model configuration choices, including mesh size and grid aspect ratio,
turbulence model, and numerical discretization schemes, in three different
code bases. Two case studies representing nearly steady neutral and
convective atmospheric boundary layer (ABL) flow conditions over nearly flat
and homogeneous terrain were used to force and assess idealized LESs, using
periodic lateral boundary conditions. Comparison with fast-response velocity
measurements at 10 heights within the lowest 100 m indicates that most model
configurations performed similarly overall, with differences between observed
and predicted wind speed generally smaller than measurement variability.
Simulations of convective conditions produced turbulence quantities and
spectra that matched the observations well, while those of neutral
simulations produced good predictions of stress, but smaller than observed
magnitudes of turbulence kinetic energy, likely due to tower wakes
influencing the measurements. While sensitivities to model configuration
choices and variability in forcing can be considerable, idealized LESs are
shown to reliably reproduce quantities of interest to wind energy
applications within the lower ABL during quasi-ideal, nearly steady neutral
and convective conditions over nearly flat and homogeneous terrain.
