Wind energy site characterization with loosely coupled mesoscale-CFD modeling

In recent years, computational fluid dynamics (CFD) simulations have been conducted to investigate wind energy problems ranging in scale from turbine blade design and tower siting to resource assessment. In this work, we investigate improvements to the simulation of the wind and turbulence field over a moderately large geographic region (~500 km²). These CFD simulations are motivated by the need for detailed flow information with resolution on the scale of a wind turbine tower. Although data from an array of meteorological towers would be ideal for characterizing a site or for model boundary conditions, it is rarely cost effective to install more than one or two meteorological towers on a potential wind farm site. Therefore, the ability to utilize alternate tools for describing the wind energy potential of a site is needed.

The Hanford Meteorological Station, a 120-meter tower on the Hanford Site in Washington State was established as part of the Manhattan Project in 1944. Over the years, additional stations have been added, and the Hanford Meteorological Network (HMN) has been developed. Many of the 26 surface stations and 4 towers of the HMN have been continuously reporting meteorological data on an hourly basis for over 25 years. This site is a valuable resource of long-term, quality-assured meteorological data that can be used to assess new tools for addressing a variety of wind energy challenges.

In this current research, we explore the effects of prescribing more detailed initial and boundary conditions to a large-scale computational fluid dynamics simulation. We examine these effects on a domain that covers a large portion of the Hanford Site. Two basic modeling cases are examined in this work. In the first case, the upwind boundary condition is prescribed using measurements available from the HMN. For the second case, the Weather Research and Forecasting (WRF) model is used to develop the upwind boundary conditions. Data from the HMN will be used in each case to evaluate the simulation results. The loose one-way coupling between the WRF model and the CFD model provides a methodology for refining estimates of winds and turbulence over wind farm sites without the expense associated with numerous measurement towers.