We at Modern Energy have extensive experience of advanced flow modelling using high fidelity CFD and mesoscale models. Our most frequently used models are WindSim, which we use for our standard wind resource calculations, and WRF which we use for regional- and mesoscale modelling as well as for long term normalization. These models are described in short below. For special applications we have also used WindModeller (Which is a wind energy wrapper around Ansys CFX) as well as general CFD models such as OpenFOAM and CFX, and reduced order model such as WAsP and FUGA (for offshore calculations).
A common consideration in all numerical modelling is the importance of understanding the strength and weaknesses of the applied simulation tool (and the underlying equations) to assess where the model can capture all relevant physics and when the results are credible. Modern Energy has over 10 years’ experience from conducting CFD and WRF simulations and validating the results against site measurements from numerus wind farms. The reference wind farms are spread over the UK, Scandinavia as well as offshore in the North Sea. This dataset includes sites in all types of terrain, varying degree of forest coverage, and sites that are exposed to a large variation of mesoscale phenomena (e.g. low-level jets, sea breeze, gravity waves of mountains and internal boundary layer build-ups). This has given us a deep understanding about the performance of the numerical models, and the most appropriate model configurations to capture the relevant physics for a given site.
WindSim
WindSim is a commercial CFD software based the RANS (Reynolds Averaged Navier-Stokes) equations. It captures the effect of atmospheric stability by including the buoyancy effects by using Boussinesq approximation and by modifying the inlet boundary conditions and boundary layer height. It also has functionality for modelling forest effects as distributed volume forces in the CFD domain.
The main benefit of using WindSim as the standard tool for wind resource assessments are:
- That it is a well-known CFD model that has been validated by many users in a large variety of situations. Through our experience with WindSim we have also conducted internal validation against site data in difficult circumstances such as forested and sites with complex terrain with fair agreement.
- The model is based on the RANS equations with methods for including atmospheric stability and forest effects. This means that all the most prominent features of the flow can be captured (as long as the flow is not close to separation, RANS models cannot accurately represent the flow field around separation regions or around very curved streamlines). These features are very important to enable use of our internal models for layout optimization based on atmospheric stability and local turbine performance (see separate sections for more information regarding atmospheric stability and local turbine performance)
- WindSim is robust and converge well also in complex terrain. We have also found it to be a relatively cost-time efficient CFD solver in terms of computational requirement.
WRF
The WRF model (Weather Research and Forecasting) is a state-of-the-art weather model which is widely used in both industry and the research environment. It is a comprehensive model which includes all relevant processes of heat, mass and momentum transfer, and can be used for simulating a wide range of weather phenomena from large synoptic scales down to meso- and even microscale.
At Modern Energy we use WRF for a multitude of applications:
- As a high-level simulation of the wind regime in a region to be used for green field & early phase screening where no site measurements are available.
- As a long-term reference dataset in wind resource assessment
- For dedicated modelling of mesoscale effects in pre-construction investigations and post-construction forensic analyses.
- To model ice conditions for our in-house pre-construction estimates & ice-loss forecasts