Page 138 - Fluid Power Engineering

W ind Resource Assessment 115

of meso- and microscale models are KAMM and WAsP. WAsP is a
microscale model that is described later in this section. Several com-
mercial companies use proprietary models to combine meso- and
microscale models. The microscale model resolves the small-scale con-
tour and roughness features.

CFD Models
Computational fluid dynamics (CFD) models are used to model: (a)
Airflow in complex terrains, for example, airflow around and over
mountains and (b) thermal effects. These models can provide a bet-
ter understanding of turbulence when fine spatial resolution is used.
CFD models are based on solving Reynolds-Averaged Navier-Stokes
(RANS) equations along with turbulence models. Two popular 3-D
CFD software programs are: WindSim and 3DWind. These programs
are used to model both meso- and microscale wind projects. Depend-
ing on the detail in the model, the 3-D CFD models can be very
computationally intensive. The output of the models is a steady-state
time-independent solution of wind speed and direction.
Inputs to CFD models are: Digital terrain model, roughness map,
and wind data at multiple locations for a year or more. The overall
process is: The spatial domain is gridded into cells; the cells may be
further nested to model features of interest; simulation is started, and
the equations are solved iteratively until steady-state is reached. The
output of the models is wind speed time series at each grid point.

WAsP, a Microscale Model
5
Wind Atlas Analysis and Application Program (WAsP) is a mi-
croscale model developed by Risø in the late 1980s (http://www.
wasp.dk/). The tool and the associated methodology have become
the most popular method of performing wind assessments at the mi-
croscale. Several of the most prominent wind assessment tools like
WindPRO and WindFarmer use the WAsP engine to perform wind
assessments.

Definitions
Microscale Model. The scale of applicability of microscale mod-

els is of the order of 100 km. Although the name may suggest
otherwise, microscale is used to perform wind assessments for
large wind farms that cover hundreds of square kilometers.
Regional wind climate (RWC). The regional wind climate is a

generalized wind statistic that describes the wind conditions
over a much larger area (order of magnitude 100 km). A gen-
eralized wind statistic is generated from observed wind data