Wind Flow Modeling: choosing between simple and advanced models?

For wind resource mapping, the traditional approach has been to rely on linear Jackson-Hunt type wind flow models developed in the 1970-90s such as WAsP, MS3DJH/MsMicro and MSFD. Coupled mesoscale numerical weather prediction (NWP) and linear wind flow models have also been in used since the end of the 1990s. Within the last few years, computational fluid dynamics (CFD) methods including Reynolds-averaged Navier-Stokes (RANS) models and large-eddy simulations (LES) have become increasingly attractive, not only for research applications but remain computationally intensive. Nevertheless, numerical wind flow modeling isn't easy. Most sites experience a wide range of atmospheric conditions, from stable to unstable thermal profiles, synoptically driven and mesoscale or thermally driven circulations, topographic and surface roughness influences, turbulence, and others. The present study aims to characterize the mean wind flow at nine different sites and evaluate the performance of three types of numerical wind flow models: (1) Jackson-Hunt type model (e.g. WAsP), (2) RANS model (referred to as RANS or CFD), (3) coupled NWP and mass-consistent model.

With the more advanced models, computing time can be very large. To keep the runtime manageable the mesoscale NWP model is typically coupled to a microscale model to achieve high spatial resolution. The two major differences between a linear or RANS model compared to a NWP model is that the former is typically run in steady-state mode and without a complete prognostic equation for temperature (i.e. conservation of energy). Therefore, the unsteadiness in the flow and thermal effects are typically not accounted for in linear and non-linear RANS models.

The wind flow models were compared against high-quality observations using 53 meteorological masts from nine project areas in North America and Europe for a total of 144 mast pairs. We will show the accuracy (in terms of RMSE) of wind flow models by terrain complexity, land cover and distance to met mast. In addition to our analysis, we will provide a review of the blind comparison study which included the results from 30 different teams and was presented at the AWEA Wind Resource & Project Energy Assessment workshop in fall 2013.